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Magmatism in the Mesozoic Extending Orogenic Process of Da Hinggan MTS
... Some investigators have suggested that the volcanic activity was triggered by the upwelling of a mantle plume ( Fig. 2a; Lin et al., 1998, https://doi.org/10.1016/j.jog.2019.01.012 Received 3 August 2018; Received in revised form 6 December 2018; Accepted 9 January 2019 1999; Shao et al., 1999;Ge et al., 1999Ge et al., , 2000, but this model has received little support (Zhang et al., 2008a;Li et al., 2014;Si et al., 2015). Fan et al. (2003) suggested that the volcanism was triggered by postorogenic diffuse extension rather than Mesozoic oceanic plate subduction or the upwelling of a mantle plume. ...
... A mantle source that has been metasomatized by slab-released fluids generally shows slight depletions or weak enrichments in Nd isotopes (Shao et al., 1999). Most of the Early Cretaceous volcanic rocks of the GXAR exhibit slightly depleted or weakly enriched Nd isotopic ratios as well as slightly enriched Sr isotopic ratios (Wu et al., 2008;Guo et al., 2010;Li et al., 2014;Yang et al., 2015a), thus overlapping the variation range of a typical IAB and the Cenozoic volcanic rocks of the Basin and Range Province in the USA ( Fig. 8; Hawkesworth et al., 1995;Rogers et al., 1995), therefore indicating a metasomatized mantle source (Fan et al., 2003;Zhang et al., 2007a, b). ...
... As time passed, the cold flat slab would have gradually warmed, and the ensuing dehydration and eclogite facies metamorphism would have caused the release of fluids into the mantle wedge and triggered partial melting of the enriched mantle. Meanwhile, the increased gravitational pull of the flat slab itself would have led to extensive foundering and the subsequent large-scale upwelling of the asthenosphere, which is consistent with the view that the asthenosphere has been undergoing uplift since the late Mesozoic in the GXAR (Shao et al., 1999). The slab break-off would have evolved quickly into large-scale post-orogenic magmatism in the GXAR ( Fig. 12d; Deng et al., in press). ...
... The DMVRB is widely covered by Mesozoic mafic and silicic volcanic rocks, with pre-Mesozoic strata being intermittently exposed. There are many polymetallic deposits in the area, including large and super-large deposits of nonferrous and precious metals, as well as rare earth element deposits (Shao et al. 1997(Shao et al. , 1998Shao and Zhang 1999;Ge et al. 2007a, b;Fan et al. 2003;Meng 2003;Wang et al. 2006;Zhang et al. 2008Zhang et al. , 2010Wu et al. 2011;Şengör et al. 1996;Li et al. 2006;Natal'in and Borukayev 1991;Zhou et al. 2009;Wu et al. 2007Wu et al. , 2011Zhou et al. 2012;Liu et al. 2004). The geodynamic setting of the DMVRB remains unresolved, with suggestions including a mantle plume origin (Lin et al. 1998;Ge et al. 1999), a basin-and-range structural setting associated with closure of the Mongolia-Okhotsk Ocean and Paleo-Asian Ocean basin Meng 2003), the influence of an extensional orogenic structure associated with Paleo-Pacific Plate subduction Zhang et al. 2008, Zhao et al. 1994, and the influence of the Mongolia-Okhotsk and the circum-Pacific tectonic systems (Shao and Zhang 1999;Wu et al. 2011;Liu et al. 2004;Meng et al. 2011;Xu et al. 2009Xu et al. , 2011. ...
... There are many polymetallic deposits in the area, including large and super-large deposits of nonferrous and precious metals, as well as rare earth element deposits (Shao et al. 1997(Shao et al. , 1998Shao and Zhang 1999;Ge et al. 2007a, b;Fan et al. 2003;Meng 2003;Wang et al. 2006;Zhang et al. 2008Zhang et al. , 2010Wu et al. 2011;Şengör et al. 1996;Li et al. 2006;Natal'in and Borukayev 1991;Zhou et al. 2009;Wu et al. 2007Wu et al. , 2011Zhou et al. 2012;Liu et al. 2004). The geodynamic setting of the DMVRB remains unresolved, with suggestions including a mantle plume origin (Lin et al. 1998;Ge et al. 1999), a basin-and-range structural setting associated with closure of the Mongolia-Okhotsk Ocean and Paleo-Asian Ocean basin Meng 2003), the influence of an extensional orogenic structure associated with Paleo-Pacific Plate subduction Zhang et al. 2008, Zhao et al. 1994, and the influence of the Mongolia-Okhotsk and the circum-Pacific tectonic systems (Shao and Zhang 1999;Wu et al. 2011;Liu et al. 2004;Meng et al. 2011;Xu et al. 2009Xu et al. , 2011. The geodynamic setting of the DMVRB belt remains an important unresolved scientific issue. ...
... and 1.9-2.0, respectively, similar to those of granites in continental crust in the Xing-Meng orogenic belt (Mcdonough and Sun 1995;Hong et al. 2000Hong et al. , 2003, indicating that the magma was derived from weakly or undepleted mantle (Shao et al. 1998;Shao and Zhang 1999). The relative deviation of the Sm/Nd ratio from the chondritic value, fSm/Nd (fSm/Nd = ( 147 Sm/ 144 Nd -( 147 Sm/ 144 Nd)CHUR)/( 147 Sm/ 144 Nd)CHUR) is in the range of 0.09 and 0.5 for the rhyolites, and slightly different from the average crustal value (0.118) indicating differentiation of 147 Sm and 144 Nd during melting and metamorphism. ...
Rhyolites with high Nb–Ta contents were recently discovered in the north Daxingan Mountains, China. We determined the geochemical characteristics and zircon U–Pb ages of these rhyolites to elucidate their tectonic setting of formation and petrogenesis. Zircons from the high Nb–Ta rhyolites are idiomorphic or hypidiomorphic, short prismatic crystals with oscillatory zoning; the zircon trace element has a higher Th/U ratio (> 0.4); zircon rare earth element (REE) content is high (average is 1729 × 10⁻⁶) and indicates heavy REE (HREE) enrichment (average is 1561 × 10⁻⁶) and shows positive Ce (Ce/Ce* = 2.1–103.4) and negative Eu (Eu/Eu* = 0.18–0.64) anomalies typical of crustal magmatic zircons. Their weighted-mean LA–ICP–MS U–Pb age of 155 ± 1 Ma indicates that they formed in the Upper Jurassic. The rhyolites are characterized by high SiO2 and alkali contents and low Fe, Ca, Mg, and Mn contents, and are weakly peraluminous, indicating that they are high-K calc-alkaline rocks. Trace element compositions are characterized by enrichments in Nb, Ta, Zr, Hf, Ce, and Rb and depletions in Sr, Eu, Ba, P, Ti, Co, and Ni, with significant positive Ce (Ce/Ce* = 2.4–2.7) and negative Eu (Eu/Eu* = 0.06) anomalies. Niobium and Ta are hosted in the zircons. In (Na2O+K2O+FeOT+MgO+TiO2) vs (Na2O+K2O)/(FeOT+MgO+TiO2) and (Al2O3+FeOT+MgO+TiO2) vs Al2O3/(FeOT+MgO+TiO2) mineral characterization diagrams, data for the samples plot in the metamorphic greywacke or basic argillaceous rock fields, indicating that the magma originated from partial melting of crustal material. εSr(t) values cover a wide range (− 18.2 to + 102.9), whereas εNd(t) values have a narrow range (1.9–2.0) with T2DM model ages of 789–785 Ma, indicating that the source was the Neoproterozoic Xinghua Ferry Group crustal basement. This crustal rock suite comprises a volcanic–sedimentary formation of metamorphosed mafic volcanic and terrigenous clastic rocks derived from a mixture of mantle and crustal materials. Residual phases in the source region include Ca-rich plagioclase, amphibole, orthopyroxene, and zircon + garnet. Together with the positive Ce anomalies and low-Sr/high-Yb characteristics of the rhyolites, this indicates that the source rocks melted at relatively shallow depths (< 30 km), low pressures (< 0.8 GPa), and high O2 fugacity. Ga × 104/Al > 2.6, Ta vs Yb, and (Rb/30) vs Hf vs (3Ta) discrimination diagrams, data for the samples plot in the A-type rhyolite and intraplate granite fields, whereas in the Nb vs Y vs Ce diagram, the data plot in the A1-type field. It is concluded that an extensional tectonic setting, resulting from closure of the Mongolia–Okhotsk Ocean at the end-Triassic, or northward subduction of oceanic lithosphere under the Siberian Plate, caused underplating of mantle-derived basaltic magma and partial melting of metamorphic crustal rocks.
... Wu et al. (2008Wu et al. ( , 2010 and Chen et al. (2009) summarized the three main views: (1) plutonism is related to the subduction of the Pacific plate to the east (Jiang and Quan, 1988;Zhao et al., 1989;Ma and Fang, 1991;Deng et al., 1996;Zhu et al., 1997;Wu et al., 2000;Zhang et al., 2010); (2) plutonism is the result of southward subduction of the northern Mongolia-Okhotsk Sea plate (Wang et al., 2002); and (3) magmatism may relate to the post-orogenic evolution of the Xing-Meng Orogenic Belt Fan et al., 2003;Lin et al., 2004). On the whole, it is broadly accepted that Cretaceous granitoid plutonism formed from magmatic underplating in an extensional withinplate tectonic environment (Shao et al., 1999a(Shao et al., , 1999b(Shao et al., , 2001. ...
... Corresponding to the tectonic evolution, the regional magmatic evolution experienced the process as follows: (1) Mantlederived magmas emplaced or cumulate xenoliths carried by dioritic magmas in the Early Mesozoic; (2) Basic dyke swarms were emplaced during the Early-Middle Jurassic; (3) Trachytic volcanic rocks, consisting of abundant mixed crust and mantle material, erupted in the Late Jurassic, and crust-mantle mixed granites or alkaline miarolitic granites were emplaced during the Late Jurassic-Early Cretaceous; (4) Finally, olivine basalt-trachyandesitepantellerite was erupted in the Early Cretaceous, prior to the emplacement of another basic dyke swarm (Shao et al., 1998(Shao et al., , 1999aZhao et al., 1989;Chen, 1997;Zhang, 1993). This magmatic evolution demonstrates that the Great Hinggan Range crust experienced a basic process; i.e., new material was being derived from the mantle and continuously injected into the crust (Shao et al., 1999b). ...
... The continental geology also indicates that emplacement of crustmantle mixed granites and asthenospheric upwelling of upper mantle basaltic magma were important modes of continental growth. The formation of the Great Hinggan Range includes a history of vertical continental crustal accretion, the continental accretion of the middle-south sections of Great Hinggan Range occurred during the Mesozoic Shao et al., 1999b). In general, this region has younger Nd model ages, supporting the view that the Late Proterozoic-Early Paleozoic was an important period of crustal growth (Cai et al., 2004;Hong et al., 2000). ...
... The majority of faults within the study area are normal or strike-slip, largely trend NE-SW, NNE-SSW, and NW-SE, with some trending N-S and E-W, and are interpreted to have formed in an extensional setting (Shao & Mu, 1999). Some of the faults record evidence for multiple stages of deformation. ...
... Orogenic granites were emplaced during continental collision, with faults controlling the formation and distribution of these Palaeozoic intrusive rocks. NE-to SW-to NNE-to SSWdirected extension during the Middle Jurassic-Early Cretaceous controlled the formation of volcanic and magmatic rocks within the Great Xing'an Range (Shao & Mu, 1999). The pre-existing faults were reactivated during the Cenozoic, deforming the Mesozoic volcanic and intrusive rocks. ...
The occurrence of igneous rocks within the Wenkutu area, northeastern China, allows the Late Palaeozoic–Mesozoic geodynamic setting of the Great Xing'an Range to be investigated. Here, we present petrographic, geochemical, and geochronological data for intrusive rocks within the Wenkutu area. Zircon U–Pb geochronology reveals that magmatism occurred during the Early Carboniferous (ca. 334 Ma), Early Permian (ca. 296 Ma), Middle Jurassic (ca. 170 Ma), and Early Cretaceous (ca. 130 Ma). The Early Carboniferous intrusive rocks are intermediate–mafic, metaluminous, and medium‐K calc‐alkaline, have low SiO2 (49.57–55.00 wt.%) and high MgO (3.00–4.77 wt.%), Cr (average 60.64 ppm), and Ni (average 24.73 ppm) contents, and high Mg# (average 45.1) values. These features, together with their significant depletion in Nb, Ta, and Ti, and their enriched Sr–Nd isotopic compositions, suggest that these Early Carboniferous rocks were derived from the mantle and subsequently contaminated by crustal material. The Early Permian, Middle Jurassic, and Early Cretaceous intrusive rocks are intermediate–acidic, peraluminous, and high‐K calc‐alkaline, enriched in light rare‐earth elements, Rb, Th, U, K, P, and Hf, relatively depleted in heavy rare‐earth elements, Nb, Ta, and Ti, and have Eu/Eu* values of 0.05–0.86. These features indicate that the rocks were derived by the partial melting of lower crust. Our results, together with those of previous studies, suggest that the Late Palaeozoic intrusive rocks formed during collision between the Songnen and Xing'an massifs. The Early Permian intrusive rocks formed during the transition from an orogenic to a non‐orogenic environment. The Middle Jurassic intrusive rocks formed during the closure of the Mongol–Okhotsk Ocean (MOO) and were emplaced along the western part of the suture zone. The Early Cretaceous intrusive rocks formed during non‐orogenic extension and were related to the final closure of the MOO or to rollback of the Palaeo‐Pacific Plate.
... Syn-orogenic granites were intruded in around 250 Ma in northern China as a result of this orogeny. Since the Late Paleozoic, the XMOB has been influenced by tectonic processes of the Mongolia-Okhotsk oceanic and the Paleo-Pacific plates, as well as the continent-continent collision between the NCC and the SC (Shao et al., 1999). ...
... Since the Middle Jurassic, intermontane molasse sediments had been deposited in the eastern XMOB (Zhu et al., 2005). In the Middle Mesozoic (J 2 -K 1 ), decompression and back-arc extension occurred and granitoids and intermediate-felsic volcanic rocks were emplaced (Qi et al., 2005;Shao et al., 1999). Since the Late Cretaceous, basalts had been erupted and continental rift basins had been formed (Zorin et al., 2001). ...
... Intrusive and volcanic rocks are extensively distributed along the major faults within the GXR during Late Paleozoic to Mesozoic and form part of a NE-SW-trending magmatic belt throughout NE China (Pang et al., 2020;Wu et al., 2011;Zhang et al., 2020;Shao et al., 1999), with the majority emplaced in three major phases: 290-270 Ma, 260-220 Ma and 155-120 Ma (Ouyang et al., 2015;Pei et al., 2018). The southern GXR contains a series of economically significant polymetallic (Mo, Cu, Sn, Fe, Au, Pb, Zn, Ag, etc.) and nonmetallic (fluorite, graphite, etc.) resources. ...
The Linxi fluorite district is located in the southern Great Xing’an Range and tectonically belongs to the eastern segment of the Central Asian Orogenic Belt. Previous studies mainly focus on the metal deposits in this region, but relatively little attention has been paid to the fluorite mineralization. The Linxi district contains more than 60 fluorite deposits while the formation age, nature of mineralized fluids, and ore-forming processes are poorly understood. This study focuses on geology, geochronology and geochemistry of the fluorite deposits in the Linxi district which share similar and relatable geological features. Fluorite veins are strictly controlled by ∼S-N-, NNE-SSW- and NE-SW-striking fault zones. Ore mineral assemblages are quite simple and mainly include fluorite, quartz and calcite. Geochronological data indicate that the main-stage fluorite vein mineralization in the Linxi district occurred approximately at 137–132 Ma. Fluid inclusions hosted in fluorite, quartz and calcite mainly homogenize at 140–220°C, corresponding to low salinities (mainly 0.3–1.2 wt% NaCl equivalent). Ore-forming fluids are characterized by low temperatures, low salinities and low densities of the H2O−NaCl system. The carbon, hydrogen and oxygen isotopic compositions of samples obtained from the Linxi fluorite district indicate an origin of meteoric water. Combined with trace element geochemistry, fluorite, quartz and calcite in this area share a common hydrothermal origin. The large-scale fluorite mineralization in this region may link to the Late Mesozoic metal metallogenic events in the southern Great Xing’an Range associated with the extensional tectonic setting.
... 321-237 Ma, Liu et al., 2014), Carboniferous-Permian and Triassic-Cretaceous granitoids intruded into the Paleozoic-Mesozoic sedimentary-volcanic strata in the western section. Mesozoic felsic magmatic activity was extensive across the whole region (140-125 Ma, Ouyang et al., 2015), mainly in a post-subduction extensional setting (Shao et al., 1999;Xu et al., 2013). Most polymetallic deposits in the region are associated with Mesozoic granitoids, with regional NE-trending compressional-shearing faults controlling deposit distribution . ...
Spatial-temporal compositional variations in hydrothermal mica from different mineralization stages were determined across a single cross-section at the Weilasituo tin-polymetallic deposit, Northeast China. Hydrothermal mica from the magmatic-hydrothermal transitional stage (unidirectional solidification textures), hydrothermal tin-tungsten stage, molybdenum stage and copper-zinc stage was analysed in situ for major and trace element composition. Weilasituo mica is enriched in Li, Rb, Cs and Zn, has a moderate W and Sn content and a low Cu content. The temporal variation in mica composition shows that the Li content decreased slightly from the early to the late stage, while Zn concentration showed the opposite trend. Other elements in mica are relatively constant between stages, with only Sn, Rb and Cs being slightly enriched in the hydrothermal tin-tungsten stage mica. According to the spatial variations in mica composition, mica with a high W, Sn, Nb and Ta content occurs in granite, while mica enriched in volatile elements like Li and F is distributed within the main tin ore vein, or adjacent to the breccia pipes. The results suggest that mica W-Sn-Nb-Ta enrichments are genetically related to an early high-temperature magmatic fluid linked to the granitic intrusions at Weilasituo, while volatile elements were enriched by successive evolution of lateral fluid migration. The trace-element content of the Weilasituo mineralizing fluid (estimated from mica composition and rough estimates of mica-fluid partition coefficients) suggests that the fluid related to different mineralization originated from the same source, and does not support obvious magmatic-meteoric fluid mixing. Finally, the results suggest that spatial-temporal variations in mica compositions can be taken as a potential indicator of ore fluid compositional evolution in a hydrothermal system.
... However, the timing of subduction remains debated. Some authors proposed that subduction took place in the Early Jurassic (Wu et al., 2011;Guo et al., 2015;Tang et al., 2016), whereas others argue that subduction began in the Middle to Late Jurassic (Lin et al., 1999;Shao et al., 1999). After extensive studies of the distribution, isotopic age, and geochemical characteristics of Jurassic granites in NE China (Wu et al., , 2011Guo et al., 2010Guo et al., , 2015, the former hypothesis is now widely accepted. ...
... The origin of the Mesozoic volcanic-intrusive rocks and the influence of subduction of the Pacific Plate on the geological evolution of NE China remain controversial. Some geologists argue that the subduction of the Pacific Plate beneath Eurasia occurred in the Middle-Late Jurassic (Lin et al., 1999;Shao et al., 1999;Zhang et al., 2001). Others have proposed that the subduction of the Pacific Plate beneath Eurasia occurred in the Early Jurassic (Sun et al., 2001;Zhang, 2002;Zhang et al., 2004;Sui et al., 2007). ...
The large-scale Tianbaoshan polymetallic (Cu, Pb, Zn, and Mo) ore district in the Yanbian area of China hosts the Xinxing Pb–Zn, Lishan Pb–Zn, Dongfeng Zn–Cu (Pb), and Dongfengbeishan Mo deposits. We report zircon U–Pb and Re–Os age data, geochemical data, and zircon Hf isotope compositions of granitic rocks associated with the Tianbaoshan ore district. Zircon U–Pb dating of the Xinxing, Lishan, Dongfeng, and Dongfengbeishan granitic rocks, all of which are associated with polymetallic mineralization, yielded weighted mean 206Pb/238U ages of 272.1 ± 2.1, 272.7 ± 1.8, 272.5 ± 2.7, and 199.6 ± 1.4 Ma, respectively. The Dongfengbeishan Mo deposit yields molybdenite Re–Os model ages of 200.3 and 190.3 Ma, an isochron age of 196.5 ± 3.1 Ma, and a weighted mean model age of 194.6 ± 2.6 Ma. This suggests that mineralization took place in the ore district in two stages during the middle Permian and Early Jurassic. The intrusive rocks of these two stages are identified as medium- to high-K calc-alkaline I-type granites. They are enriched in large ion lithophile elements, depleted in high field-strength elements, and contain positive zircon εHf(t) values (+4.6 to +13.9), indicating the primary magma originated from the partial melting of juvenile lower crust. The granitic rocks show geochemical characteristics similar to those of coeval rocks in NE China. Based on the new geochemical data and other regional geological studies, we propose that the mineralization of the two stages of granitic rocks in the Tianbaoshan polymetallic ore district occurred in active continental margin settings, but was controlled by different geotectonic mechanisms: the subduction of the Paleo-Asian Oceanic Plate in the middle Permian and the subduction of the Paleo-Pacific Plate in the Early Jurassic.
... The closure time of Mongol-Okhotsk Ocean is still controversial (Ren et al. 1992;Yin and Nie 1996;Chen et al. 2007a). A group of researchers considered that the Siberia continent collided with the united North China-Mongolia plates during the Middle to Late Jurassic, causing deformation and metamorphism of pre-Mesozoic rocks Tang 1996, 2015;Shao and Zhang 1999;Hu et al. 2004;Zhao et al. 2004;Deng et al. 2005;Wu et al. 2010a;Chen et al. 2012); by contrast, another group of researchers (e.g., Kravchinsky et al. 2002;Tomurtogoo et al. 2005;Sorokin et al. 2007;Ruzhentsev and Nekrasov 2009) suggested that the Mongol-Okhotsk Ocean diachronously closed eastward from mid-Jurassic to Early Cretaceous. As a matter of fact, the western part of NNCC and Great Hingan Range contain abundant mid-Yanshanian volcanic rocks (Manketouebo Formation), called "Great Hingan Mesozoic Igneous Province" (Sengor and Natal'in 1996), with the oldest age of 165.8 ± 2.8 Ma (zircon U-Pb age) obtained from southern Great Hingan Rang , and the youngest age of 129.7 ± 1.6 Ma (zircon U-Pb age) obtained from northern Great Hingan Range Chen et al. 2016b and references therein). ...
The North China Craton (NCC) was finally formed at ca. 1850 Ma and then kept its stability and uniformity until the Mesozoic decratonization. After the closure of the Paleo-Asian Ocean in Late Permian and the northernmost Paleo-Tethys Ocean in end-Triassic, the NCC continuously collided with the Siberia Craton to the north and the South China Block to the south, followed by subduction of the Mongol–Okhotsk and Pacific oceanic plates. These significant Mesozoic tectonic events destructed the NCC's stability and uniformity, and caused intensive hydrothermal mineralization of Mo, Au, Ag, and other metals. The NCC is the most important Mo province in the world, with the Mo deposits being concentrated at the southern and northern margins of NCC. In this contribution, we briefly summarize the geology, geochemistry and isotope ages of the Mo deposits in the northern NCC (NNCC), overview the progresses in understanding the ore geneses and tectonic settings, and setup a linkage between the mineralization and orogenies which resulted in the decratonization of the NCC. All the Mo-only or Mo-dominated deposits were formed after the closure of the Paleo-Asian Ocean, and in a series of pulses around 250–200, 200–160, 160–130 and <130 Ma (130–100 Ma). Main genetic types are porphyries (including breccia pipes), skarns and quartz veins, with the porphyry systems being predominant. The porphyry Mo deposits can be further subdivided into three subtypes, i.e., collision-or Dabie-, rift-or Climax-, and subduction-or Endako-types. The Mo deposits aged 250–200-Ma and 200–160-Ma belong to collision-type and have been formed in syn-to post-collisional tectonic setting. The 160–130-Ma Mo mineralization mainly occurs in the central NNCC and are predominated by the Climax-type porphyry Mo systems, which resulted from a back-arc rift related to southward subduction of the Mongol–Okhotsk oceanic plate. The 130–100-Ma deposit belongs to Endako-type and are only located in the eastern part of the northern NCC, which must be related to the westward subduction of the Paleo-Pacific oceanic plate. As shown by the porphyry Mo deposits in NNCC, the mineral systems are a powerful indicator of tectonic settings and associated evolutionary trends.
... The closure time of Mongol-Okhotsk Ocean is still controversial (Ren et al., 1992;Wang and Mo, 1995;Yin and Nie, 1996;Chen et al., 2007a). A group of researchers considered that the Siberia continent collided with the united North China-Mongolia plates during the Middle to Late Jurassic, causing deformation and metamorphism of pre-Mesozoic rocks (Shao and Zhang, 1999;Zhao et al., 2004;Hu et al., 2004;Deng et al., 2005;Wu et al., 2010a;Chen et al., 2012b). In contrast, another group of researchers (e.g., Kravchinsky et al., 2002;Tomurtogoo et al., 2005;Sorokin et al., 2007;Ruzhentsev and Nekrasov, 2009) suggested that the Mongol-Okhotsk Ocean diachronously closed eastward from mid-Jurassic to Early Cretaceous. ...
... Zeng et al. (2012aZeng et al. ( , 2013 propose that the large-scale Mo (Cu, W, and Pb-Zn) mineralization occurring in northeast China formed in three tectonic settings. Based on a series of mafic dike swarms and abundant magmatic activity that evolved from calc-alkaline, to alkali-calcic, to alkaline series, Shao et al. (1999Shao et al. ( , 2001 and Zhai et al. (2004) propose that the lithosphere in Northeastern China was continuously in extension during the Early Cretaceous and that the large-scale metallogenesis was related to this extension regime. Geochronological information in this study indicates that the Mo mineralization in the Xilamulun Mo belt also occurred in the Late Jurassic as well as the Early Cretaceous and is related to the extension stage under the transformation tectonic regime, which is also proved by the geochemical information of the Late Jurassic granitoids. ...
The Xilamulun Mo belt of Northeastern China, located in the southeastern segment of the Central Asia Orogenic Belt (CAOB), is composed of large deposits of porphyry Mo and quartz-vein-type Mo, which are related to Mesozoic granitoids. Previous studies led to the conclusion that all granitoids in the region formed during the Cretaceous and Triassic, but our new laser ablation inductively coupled plasma mass spectrometry U–Pb zircon dating of magmatic zircons from five samples of four mineralized plutons (Nailingou, Longtoushan, and Hashitu granites and Erbadi and Hashitu granite porphyries) reveals that these range in age from 143.8 ± 1.2 to 149.5 ± 1.0 Ma. These granites show post-collisional (A-type) geochemical characteristics (e.g. enrichment in total alkali, LILE, and LREE and depletion in Eu, Ba, P, and Nb). The Erbadi, Longtoushan, Hashitu, and Longtoushan granitoids exhibit moderately positive Hf isotopic compositions (εHf(t) = −0.3 to 10.2), indicating that granitic magmas may reflect mixtures of mantle melts and continental crust. These mineralized granites were all emplaced along a major fault over a time span of ~6 million years during the Late Jurassic. We conclude that igneous activity and mineralization resulted from the rollback of the subducted Palaeo-Pacific plate beneath Eurasia. Confirming that the Late Jurassic granitic intrusives are related to the Mo mineralization is useful for understanding the Mesozoic tectonic evolution of the Xilamulun Mo belt and also has significant implications for the regional exploration of ores.
... But the bimodal igneous rock assemblage formed in Late Indosinian period, which indicate the lithospheric thinning and crustal extension. The lithospheric thinning and crustal extension may be caused by the upwelling of asthenosphere and underplating in post-orogenic period [35], which may be produced the new depleted lithospheric mantle, the partial milting of the depleted lithospheric mantle formed the primitive magma of the mafic-ultramafic complexes. ...
There are series of Cu-Ni sulfide-bearing mafic-ultramafic intrusions widespread in north JilinProvince,Northeastern China. The intrusions formed in Xing’an-Mongolian Orogenic Belt near to the northeastern margin of North China Craton. The complexes were formed in almost same period according to the zircon U-Pb dating reported recently, which means that the complexes were formed in same tectonic period and belong to one tectonic magmatic event. The rock assemblages are different from the ophiolite type and Yidun type in orogenic belt. The mafic-ultramafic complexes formed in the range from 217 Ma to 232 Ma coeval with A-type granites in the area, which formed bimodal igneous rock assemblage. According to the regional angular unconformities, there were existed the orogenies of Caledonian, Hercynian, Early Indosinian, Late Indosinian and Yanshanian. The Early Indosinian coeval with orogenic I-type granites and sanukitie that suggesting the lithosphere thickening in the extrusion tectonic setting of orogenic processes, however the Late Indosinian coeval with bimodal igneous rock assemblage that suggesting the lithosphere thinning in the extension tectonic setting of post-orogenic processes in the Xing’an-Mongolian Orogenic Belt. Chemical composition of the mafic-ultramafic rocks has the characteristics of high-Mg and low-K tholeiites related with inter-continental post-orogenic tectonic setting. The trace elements indicate their formed in conditions of continental extension belt or initial rift and has the characteristics of revolution from oceanic island arc, volcanic arc of continental margin to continental extended belt. The low initial Sr isotopic ratios and positive eNd(t) values suggest that the initial magma of the complexes come from the parting melting of depleted lithospheric mantle. The depleted ithospheric mantle was new formed supported by zircon Hf isotope in Hongqiling complex. The depleted lithospheric mantle may be caused by the asthenosheric mantle upwelling and underplating in the tectonic setting of extension during the Late Indosinian post-orogenic processes.
... Gold, silver and base metal ore deposits are contemporaneous with the regional extension and related magmatism in northeast China (Liu et al., 2011a;Shao and Wang, 2003;Shao and Zhang, 1999;Wu and Sun, 1999). Mineralization associated with the magmatism is already well documented in both northern and southern China, where gold and base metal mineralization is coeval and genetically associated with extension and magmatism (Fan et al., 2003;Mao et al., 2003a,b;Sun et al., 2007;Yang et al., 2003). ...
... 120 Ma, which correspond with collisional orogeny, tectonic regime transformation and large-scale delamination of lithosphere background (Chen et al., 1998;Mao et al., 2005Mao et al., , 2010Zhai et al., 2001;Zhang et al., 2010b). Shao et al. (1999Shao et al. ( , 2001 and Zhai et al. (2004) propose that the lithosphere in northeast China was continuously in lithosphere extension in the Early Cretaceous on the basis of a series of mafic dike swarms and abundant magmatic activities which evolved from calc-alkaline, to alkali-calcic, to alkaline series. The large-scale Mo, Mo-W and Mo-Cu mineralization occurred in northeast China was related to this extension regime. ...
The Aolunhua porphyry Mo–Cu deposit is located in the northern margin of the North China Craton (NCC), and belongs to the northern part of the Xilamulun metallogenic belt. More than 90% of the mineralization occurs within the Aolunhua monzogranite-porphyry; a small part is hosted within quartz veins that crosscut Late Permian strata. The syenogranite, occurring as dikes and cutting through the Aolunhua monzogranite-porphyry, is radially distributed in the mining district. Zircon U–Pb ages show that the Aolunhua monzogranite-porphyry and the post-ore syenogranite have concordant 206Pb/238U ages of 138.7±1.2Ma and 131.4±2.8Ma, respectively. Based on analyses of major, trace elements and Hf-isotopes, the Aolunhua porphyry is characterized by high Sr low Y with high La/Yb and Sr/Y ratios typical of adakitic granites, whereas the post-ore syenogranite has lower Sr and higher Y values, showing apparently negative Eu anomalies (δEu=0.26 to 0.31). The Hf isotopic composition of the Aolunhua porphyry [εHf(t)=+3.6 to +9.2] and the post-ore syenogranite [εHf(t)=+3.6 to +8.7] indicates that both juvenile crustal sources and depleted mantle contributed to their origin. The regional geological setting together with the discrepancy of geochemistry between the Aolunhua porphyry and the post-ore syenogranite probably indicates that they formed in different tectonic regimes. The Aolunhua porphyry is derived from partial melting of the thickened crust due to underplating of the basaltic magma under the transformation tectonic regime, while the post-ore syenogranite comes from the crustal root melting during the lithospheric delamination stage under the lithosphere thinning regime of northeast China.
Recognition of the sources of metals and fluids is crucial to determine the genesis of gold deposits, especially in distinguishing the orogenic and magmatic hydrothermal deposits. There is no consensus on the source and genetic style of the Mesozoic gold deposits in the North China Craton (NCC). The Taijiying gold deposit in the Chifeng-Chaoyang gold district on the northern margin of the NCC is a medium-sized gold deposit and worth studying for its sources of metals and fluids. It is hosted by amphibole- to granulite-facies metamorphic rocks and Mesozoic intrusions, and controlled by NNE-, NE-trending compressional reverse faults and NW-trending extensional normal faults. The gold mineralization types include auriferous quartz veins and wall rock alterations of phyllic mineralization, pyritization, chloritization, and carbonatization. According to the crosscutting relationships of the veins and the mineral textures within the ore-bearing veins, four mineralization stages are recognized: clouded-white quartz ± pyrite (stage I), gray quartz + pyrite (stage II), quartz + polymetallic sulfides (stage III), and calcite ± quartz (stage IV), among which the stages II and III represent the main gold mineralization stages. The timing of the gold mineralization is constrained to the Middle Triassic by zircon U-Pb ages of a pre-metallogenic diorite (258.0 ± 1.9 Ma) and a ore-related granitic porphyry dike (241.5 ± 2.2 Ma). Three types of fluid inclusions (FIs) in the quartz veins of four stages are identified: vapor-rich (type 1), CO2-H2O three-phase (type 2), and liquid-rich FIs (type 3). Their trapping temperatures gradually decrease from 352 ℃ (stage I) to 124 ℃ (stage IV), with salinities decreasing from 9.8 to 2.0 wt.% NaCl eqv., indicating that the ore-forming fluids belong to a H2O-NaCl-CO2 system. The first three stages were characterized by moderate-high temperatures, a large variation in salinities, akin to those of the magmatic hydrothermal fluids. The H-O isotope compositions from the stage II (δ¹⁸Ow = 4.1-4.8‰ and δD = -110 to -87‰) to the stage III (δ¹⁸Ow = 3.5 to 3.7‰ and δD = -101 to -98‰), indicate that the ore-forming fluids were mainly magmatic fluids. The δ³⁴SV-CDT (1.7-2.1‰), Pb isotopes (²⁰⁶Pb/²⁰⁴Pb = 15.09-15.90, ²⁰⁷Pb/²⁰⁴Pb = 15.00-15.15, ²⁰⁸Pb/²⁰⁴Pb = 35.76-37.97), and Os isotopes (initial ¹⁸⁷Os/¹⁸⁸Os = 2.3±1.0) of the Au-bearing pyrite samples at the stages II and III, similar to those of the crust-derived magma, suggest that the gold and other metals were extracted from the partial melting of the lower crust. Accordingly, the Taijiying gold deposit is probably a magmatic hydrothermal deposit. The areas recording the Triassic batholith with a developed fault system would be prospective targets for gold mineralization in the Chifeng-Chaoyang district on the northern margin of the NCC.
The Haobugao Pb–Zn deposit located in the southern Great Xing’an Range (SGXR) is one of the most important deposits within the Huanggangliang–Ganzhuermiao polymetallic metallogenic belt. Xiaohanshan quartz monzonite porphyry and Wulandaba granodiorite are present in the ore area and are assumed to be closely related to the mineralization. In this study, a new isotopic dating technique, zircon U–Pb laser ablation inductively coupled plasma mass spectrometer analysis, was applied to the granites; the analyses indicate that the Xiaohanshan quartz monzonite porphyry and Wulandaba granodiorite were emplaced at 143.9 ± 1.1 Ma and 151.3 ± 1.4 Ma, respectively. Geochemically, these A-type granites are characterized by relatively high SiO2 and K2O contents, low Al2O3 content, and negative Eu anomalies. Additionally, both granites display strong Rb, Th, U, and Ce enrichment and Ba, K, Sr, and Ti depletion. Their relatively high εHf (t) values (with averages of 7.13 and 7.87, respectively) and young two-stage Nd and Hf model ages indicate that the two granites may have predominantly derived from the partial melting of a juvenile lower crust, followed by fractional crystallization during magma ascent. The geological, elemental, and isotopic evidence shows that the Xiaohanshan quartz monzonite porphyry and Wulandaba granodiorite formed due to the upwelling of mantle-derived alkaline magma and partial melting of the crust, with a certain degree of mixed dyeing, under a tectonic background of asthenosphere upwelling and lithosphere extension via the subduction of the ancient Pacific plate.
The large-scaled Mesozoic volcanic activities in the Great Xing'an Range, northeastern (NE) China, have received extensive attention recently. However, the details of the tectonic setting and geodynamic processes of the Late Mesozoic time are still controversial. In this paper, we examined the geochronology and geochemistry of the Late Mesozoic volcanic rocks collected from the southern Great Xing'an Range, in order to constrain the tectonic evolution of the Great Xing'an Range in the Late Mesozoic time. The compiled data show that the Late Mesozoic volcanic rocks can be divided into three stages: Middle-Late Jurassic felsic volcanic rocks (174–148 Ma), Early Cretaceous intermediate and intermediate-felsic volcanic rocks (142–125 Ma, peak at 138 Ma) and Early Cretaceous felsic volcanic rocks (140–120 Ma, peak at 125 Ma). The Middle-Late Jurassic felsic volcanic rocks in the southern Great Xing'an Range are geochemically similar to A-type granite or highly fractionated granite, which have εHf(t) values of (−0.7 to +12.1) and Hf two-stage model (TDM2; 549–1714 Ma), indicating they are derived from the magma generated by partial melting of thickened juvenile lower crust and formed in a post-collisional extensional setting related to subduction of the Mongol–Okhotsk oceanic plate. The Early Cretaceous intermediate and intermediate-felsic volcanic rocks have the characteristics of active continental margin arc, which have εHf(t) values of −11.6 to +13.0 and TDM2 ages of 449–2670 Ma, suggesting that these rocks are the product of partial melting of lithospheric mantle. They are metasomatized by subduction-derived fluids or melts and related to the flat-slab subduction of the Mongol-Okhotsk oceanic plate beneath the Great Xing'an Range after the rapid closure of the Mongol-Okhotsk Ocean. The Early Cretaceous felsic volcanic rocks in the study are dominated by A-type rhyolite, which are associated with coeval A-type granites, metamorphic core complexes and rift basins, suggesting they formed in an extensional environment related to either the subduction of the Paleo-Pacific oceanic plate beneath the Eurasian continent or the massive upwelling of the asthenosphere following the collapse of the Mongol–Okhotsk oceanic plate.
This study presents new zircon U–Pb ages, Sr–Nd–Hf isotopic data, and whole‐rock geochemical data obtained from the Early Cretaceous volcanic rocks from the north‐western Great Xing'an Range, Northeast China, to constrain the late Mesozoic magmatism and geodynamic setting of this region, which is located in the eastern segment of the Central Asian Orogenic Belt (CAOB). Zircon U–Pb age determinations show that the studied samples formed at 124–114 Ma with an Early Cretaceous magmatic event produced voluminous felsic and minor mafic volcanic rocks. The mafic rocks are dominantly basalt and basaltic andesite, with relatively low SiO2 contents (49.88–56.64 wt.%). These rocks are enriched in Th, U, large‐ion lithophile elements (LILE; e.g., Rb, Ba, and K) and light rare‐earth elements (REEs), and depleted in high‐field‐strength elements (HFSE; e.g., Nb, Ta, and Ti) and heavy REEs (Yb and Lu). The rocks have εNd(t) values of 0.44–0.75 and initial 87Sr/86Sr ratio of 0.70499–0.70548. These results indicate that the mafic rocks were derived from the partial melting of enriched lithospheric mantle that had been previously metasomatized by subduction‐related fluids and experienced variable amounts of fractional crystallization and moderate crustal contamination. In contrast to the mafic rocks, the felsic rocks are dominantly peraluminous trachytes, rhyolites, and dacites with high SiO2 contents and low MgO contents. These felsic rocks display enriched and variable concentrations of LILEs and REEs, show negative Eu anomalies, and have εHf(t) values of +2.6 to +8.3 with TDM2 ages of 1,014–655 Ma, indicating they were derived from partial melting of juvenile crustal materials. These Early Cretaceous igneous rock assemblages record a post‐collisional lithospheric extensional setting resulting from the closure of the Mongol–Okhotsk Ocean, consistent with the results of previous studies on the contemporaneous tectono‐magmatic activities in NE China.
The Dacaoping and Sadaigoumen Mo deposits were recently discovered along the northern margin of the North China Craton. In this paper, we present new zircon U–Pb ages, Hf isotope data, and whole-rock major and trace element data for the monzogranite and granodiorite in the Dacaoping Mo deposit and the monzogranite in the Sabagaogoumen Mo deposit, and we use these data to constrain the metallogenic epoch and the tectonic background in the area. Combined with previous data, we suggest four phases of mineralization in the Dacaoping and Sabagaogoumen Mo deposits; these phases are 248 Ma, 236 Ma, 147 Ma, and 140 Ma. The Early Triassic monzogranite and Early Cretaceous granodiorite in the Dacaoping Mo deposit and the Middle Triassic monzogranite in the Sabagaogoumen Mo deposit are I-type granite with similar geochemical characteristics. The Triassic granites formed in a collisional–post-collisional setting between the North China plate and the Siberian plate, and the Cretaceous granodiorite formed from the rapid thinning of the lithosphere. Their source rock should mainly originate from the partial melting of ancient crustal material. Compared with other Mo deposits in the region, we can further divide these Mo deposits into three phases, namely (1) Triassic (ca. 248–223 Ma), (2) Early–Middle Jurassic (ca. 187–165 Ma), and (3) Late Jurassic–Early Cretaceous (ca. 155–130 Ma), which are consistent with the times of magmatic activity. These activities occurred during the collision and post-collision between the North China plate and the Siberian plate after the Paleo-Asian Ocean’s closure, intracontinental orogeny, and rapid thinning of the lithosphere, respectively.
The large Bayanbaolege Ag polymetallic deposit is one of the newly discovered deposits in the Tuquan-Linxi Fe (Sn)-Cu-Pb-Zn-Ag-Nb (Ta) metallogenic belt of the Southern Great Xing’an Range, NE China. Its major ore bodies, sulfide-quartz veins, are distributed within granodiorite porphyry and in adjacent Late Permian strata. According to ore-forming geological conditions, mineralization and alternation characteristics, source and features of ore-forming fluid, as well as metallogenic depth (<1.45 km), the Bayanbaolege deposit belongs to the mesothermal vein type, and has a genetic relationship with the granodiorite porphyry. Three mineralization stages have been recognized, namely, arsenopyrite-pyrite-quartz (stage I), chalcopyrite-pyrite-sphalerite-quartz (stage II) and calcite-galena-silver minerals (stage III). The zircon U-Pb age of the granodiorite porphyry (130 ± 1 Ma, MSWD = 1.8), indicates that the Ag polymetallic mineralization took place in the Early Cretaceous period. Microthermometric measurements and laser Raman analyses of four types of fluid inclusions that formed in the three stages show that the ore-forming fluid belongs to the H2O-CO2-NaCl system, with medium temperatures (mean temperatures, stage I: 368 °C; stage II: 286 °C; stage III: 206 °C) and medium-low salinities (mean salinities, stage I: 2.1–7.6 wt% NaCl equivalent; stage II: 1.6–11.6 wt% NaCl equivalent; stage III: 1.2–8.4 wt% NaCl equivalent). C-H-O isotope data indicate that ore-forming fluid was derived largely from magmatic fluid, with the addition of meteoric water in the later stage.
The Dacaoping and Sadaigoumen Mo deposits were recently discovered along the northern margin of the North China Craton. The newly determined Re–Os isochronous age of molybdenite from the Dacaoping Mo deposit is ca. 147 Ma, and the Re–Os model age of molybdenite from the Sadaigoumen Mo deposit is ca. 248 Ma, which represents two of their respective mineralization stages. Combined with previous data, we suggest four phases of mineralization in the Dacaoping and Sabagaogoumen Mo deposits; these phases are 248, 236, 147, and 140 Ma. The Early Triassic monzogranite and Early Cretaceous granodiorite in the Dacaoping Mo deposit and the Middle Triassic monzogranite in the Sabagaogoumen Mo deposit are I‐type granite with similar geochemical characteristics. The Triassic granites formed in a collisional–post‐collisional setting between the North China Plate and the Siberian Plate, and the Cretaceous granodiorite formed from the rapid thinning of the lithosphere. The partial melting of the lower crust is the main reason for their formation, and small amounts of mantle‐derived components were added. Compared to other Mo deposits in the region, we can further divide these Mo deposits into three phases, namely, (a) Triassic (ca. 248–223 Ma), (b) Early–Middle Jurassic (ca. 187–165 Ma), and (c) Late Jurassic–Early Cretaceous (ca. 155–130 Ma), which are consistent with the times of magmatic activity. These activities occurred during the collision and post‐collision between the North China Plate and the Siberian Plate after the Paleo‐Asian Ocean's closure, intracontinental orogeny, and rapid thinning of the lithosphere, respectively.
The mechanism that triggered large-scale Late Mesozoic magmatism in the northeastern Great Xing’an Range (NE GXAR) is strongly controversial. In this paper, we present whole rock geochemistry and zircon trace element, U-Pb and Hf isotopic data on the volcanic rocks in the Longjiang and Guanghua formations in the northeastern Xing’an Block. Zircons with ages of 120–119 Ma indicate that these volcanic rocks were formed in the Early Cretaceous. Combined with previous data, it is clear that volcanic rocks in the NE GXAR erupted between 128 and 108 Ma. The andesite samples of the Longjiang Formation show high contents of Al2O3, CaO, and MgO, significant negative Nb, Ta, and Ti anomalies; εHf (t) values of zircons from the andesite sample vary from +4.13 to +7.67, indicating an enriched mantle source. The rhyolites of the Guanghua Formation show high SiO2 and K2O concentrations, low P2O5, MgO, Cr, and Ni contents and Mg# values. The positive εHf (t) values (+5.72 to +10.58) with two-stage Hf model ages ranging from 939 to 701 Ma indicate that the rhyolites are derived from the partial melting of basaltic lower crust. Combined with the regional geological evolution, we conclude that the generation of the Early Cretaceous volcanic rocks in the NE GXAR might be triggered by the dehydration, disintegration, and foundering of the Mongol-Okhotsk Oceanic flat-slab and the subsequent upwelling of the asthenosphere.
The Chalukou deposit is located in the North Great Xing’an Range of the Xing’an-Mongolia Orogen bordering and to the northeast of the North China Craton. The deposit is a high-F-type porphyry Mo deposit hosted by the Chalukou composite igneous body containing small intrusive bodies genetically related to Mo mineralization. The composite igneous body includes pre-mineralization dolerite, monzogranite and syenogranite, syn-mineralization rhyolitic porphyry, granitic porphyry and fine-grained monzogranite, and post-mineralization rhyolitic porphyry, quartz porphyry, dioritic porphyry and andesitic porphyry. Detailed laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon dating of the igneous components of the composite igneous body was carried out to determine the temporal framework for magmatism in the Chalukou region. The new LA-ICP-MS U-Pb ages constraint documented here, together with the published ages, indicate that there was a protracted porphyry Mo ore-forming event of approximately 7 million years between ca. 152 when the ore related rhyolitic porphyry was emplaced and ca.145 Ma when molybdenite ceased being deposited. The dating reveals that the mineralization is a part of relatively long-lived magmatic cycle involving the emplacement of small doleritic stocks at ca. 165 Ma that progressively evolved into extensive granitic intrusions at ca. 164 Ma, and then diminished with the emplacement of mineralization-related porphyries to ca. 152 Ma. The emplacement of barren Early Cretaceous magmatism, represented by volcanic units in the ca. 136 Ma Guanghua Formation and porphyries, followed the mineralized magmatism.
Six mafic dyke swarms crop out in Hebei Province within the Taihang-Da Hinggan gravity lineament magmatic belt, China, and were sampled. Here, we present new zircon laser ablation-inductively coupled plasma-mass spectrometry U-Pb age, whole rock geochemical, and Sr-Nd-Pb-Hf isotopic data for the six areas where these mafic dykes occur. The mafic (dolerite) dykes formed between 131.6 ± 1.6 and 121.6 ± 1.1 Ma, and are enriched in the light rare earth elements (LREE), some of the large ion lithophile elements (LILE; e.g., Rb, Ba, and Sr) and Pb, and are depleted in Th, U, Nb and Ta; some samples are also depleted in Eu. The dykes have high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7055-0.7057), negative εNd (t) values (-12.5 to −11.9), relatively constant Pb isotopic ratios ((²⁰⁶Pb/²⁰⁴Pb)i = 16.45-16.51, (²⁰⁷Pb/²⁰⁴Pb)i = 15.44-15.51, (²⁰⁸Pb/²⁰⁴Pb)i = 36.49-36.53), negative εHf (t) values (-18.2 to −15.1), and old Nd (TNdDM2; 2.17-2.47 Ga) and Hf (THfDM2; 2.28-2.33 Ga) model ages. These geochronological, geochemical, and isotopic data indicate that the dykes were derived from magmas generated by low to moderate degree partial melting (1.0%-10%) of an EM1-like garnet lherzolite mantle source; these magmas fractionated olivine, clinopyroxene, and hornblende prior to emplacement, and assimilated minimal amounts of crustal material. Several possible models have previously been proposed to explain the origin of Mesozoic magmatism in this region. However, here we propose a foundering model for these studied mafic dykes, involving the foundering of eclogite from thickened lower crust due to the collision between the Siberian Craton and the North China Craon.
Laodaokou unit is located in Oroqen Autonomous Banner, Inner Mongolia, the east of Xing'an Mongolian orogenic belt, northern Great Xing'an Range. The unit is mainly composed of diorite, adamellite, and dioritic porphyrite. SIMS U-Pb dating of zircon of the diorite provides the age of (126.09±0.95) Ma, indicating that the plution was formed in Early Cretaceous instead of Cambrian as thought before. The major element data show that the diorites contains 56.13%-57.91% of SiO2, 0.97%-0.99% of TiO2, 2.00%-2.12% of MgO, 6.73%-7.41% of TFe2O3, 36.00-38.00 of Mg#, 4.29%-4.53% of Na2O, 1.38%-1.59% of K2O, 17.95%-18.36% of Al2O3. The K2O/Na2O ratios range from 0.31 to 0.37. The diorites are rich in alumina and sodium relatively. The rare earth elements chondrite standardized curves show that they are rich in light REE and depleted of heavy REE with weak negative δEu (0.85-0.87). Laodaokou plution is rich in large ion lithophile element (LILE) (e.g., Ba, K, Rb, Th, U), but depleted of high field strength elements (HFSE) (e. g., Nb, Ta, Ti, and P). The geochemical signatures above imply a characteristic related to subduction, and this suggests that the magmatic source of Laodaokou diorites were from the lithospheric mantle, which was metasomatosed by subduction fluid. Combining with the geochemical characteristics of Laodaokou plution and its regional tectonic settings, we conclude that the plution might be formed under a lithospheric extension after the closure of Mongolia-Okhotsk Ocean.
The Taihang - Da Hinggan Mountains Tectonomagmatic Belt is the Mesozoic magmaeric activities concentrating area in eastern China, which passes through the two tectonic units of the North China Craton and the Inn Mongolian Orogenic Zone. In this paper a systematic geochemical study on Nd, Sr and Pb isotopic characteristics from more than 40 typical complexes along the tectonomagmatic belt is presented to indicate that the Mesozoic intrusives in different sections of this belt (mainly the north, south Taihang Mountains and the middle-south Da Hinggan Mountains), even those of different stages (mainly three stages) in the same section have entirely different Nd, Sr and Pb isotopic characteristics, which reveals that their source regions are different. The source rocks in the southern section of Taihang Mountains are related to materials from the enriched mantle reservoir. In the northern section the early stage basic-intermediate rocks are mainly formed by the partial melting of materials from the enriched mantle, the main stage intermediate-acid ones have a close connection to materials from the lower crust, while the late stage alkali-rich ones are even derived from those from the lower-middle crust. And the intermediate-acid magma in the middle-south Da Hinggan Mountains is mainly originated from depleted mantle materials. These also reveal that the lithospheric mantle below the North China Craton is enriched and that below the Inner Mongolia Orogenic Zone is depleted. In addition, implicated by Nd depleted mantle model ages (TDM) , 2543 ∼ 1485Ma probably represents the time for mantle enrichment beneath the North China Craton, and 983 ∼ 540Ma (Proterozoic to early Palaeozoic period) suggests one of the main stages for the crust growth in Da Hinggan Mountains area.
The Dajing deposit is an important tin-polymetallic in Inner Mongolia, North China. The hypabyssal dikes, which are closely coexisting with ore veins in deposit, are extensively developed. The previous chronology studies show that both the dikes and ore veins were generated in Mid-Late Yanshanian Period in this study area, so the deposit was regarded to be magmatic hydrothermal type deposit, which related to the activities of the subvolcanic dike swarms in this area. We obtain the zircon LA-ICP-MS U-Pb ages of dacite porphyry and felsite dikes, which are widely distributed in the deposit and were considered to be closely connected with the genesis of the deposit. The zircon U-Pb ages are 240Ma and 239Ma for the dacite porphyry of DJ-7 and YX-20 respectively, and 162 ± 1 Ma for felsite dike of DJ-1. These results implicate that the dikes were formed in Early Indosinian and Middle Yanshanian in the deposit area. Combining with the previous regional research, these results indicate that the dacite porphyry was formed in syn-orogenic to post-orogenic setting, and felsite was formed in post-orogenic setting. Because of the 140Ma ore-forming age, we concluded that the dikes in the ore areas have no obvious relationship with the deposit genesis. However, it provided the advantageous space for the formation of the ore veins.
The Xiaodonggou porphyry molybdenum deposit located in the Xarmoron molybdenum metallogenic belt is chose as the research area. The Xiaodonggou pluton is rich in silicon, potass, zirconium, and low in REE. It has no or small negative Eu anomaly and shows an isotopic composition high in εNd(t) and low in Sri, indicating its magma origining from the melting of juvenile thicken lower crust In the meanwhile, it contained the features of high temperature, quick melting, quick segregation. The SHRIMP zircon UPb dating gives a result of 142 ± 2Ma, corresponding to the big tectonic transition period of 140Ma, when the major stress field changing from NS to WE. At that time, the Da-Hinggan Mountains area was under an extensive tectonic background, underplating proceeded and mantle materials could add into the magmas forming in the lower crust. The common lead analysis of the pluton orthoclases and molybdenites shows that the former transfer from orogen to mantle and the latter come from mantle, demonstrating that the rock, and ore-forming materials of the deposit have different sources, magma from the lower crust mixing with mantle fluid. From the above analysis, with the physical experiment results of the water-magma reaction, we propose the following model, for the Xiaodonggou porphyry molybdenum deposit. In the Early Cretaceous period, the Da-Hinggan Mountains area was under an extensive tectonic background, the adding of mande fluid containing ore materials into heated lower crust made it melt to produce magmas. Following more mantle fluid got into the magma room, and urged, the magma to escape from the source quickly. The fluid and magma uplifted together, when they arrived at shallow depth, the fluid-magma became unstable and the latter was broken into many small agglomerates with fluid connecting them in the interspaces. Because of the H+,K + and various elements existing in the fluid, it would reacted with the magma and the rock through alteration and ore minerals crystallized out, forming the Xiaodonggou porphyry deposit with disseminated mineralization phenomenon.
In the Mesozoic, the Northeast (NE) China experienced transformation from Mongol-Okhotsk (MO) to circum-Pacific tectonic regime, forming different temporal volcanic activities. This paper summarizes geochoronology, spatial-temporal variations, association and geochemistry, with the aim to constrain evolution of those two regimes. Together with previous information, U-Pb age data indicate that Mesozoic volcanism in NE China can be subdivided into five episodes: Early-Middle Jurassic (190 ∼ 160Ma), Late Jurassic (160 ∼ 145Ma), early Early Cretaceous (145 ∼ 120Ma), late Early Cretaceous (120 ∼ lOOMa), and early Late Cretaceous (100∼90Ma). The Early-Middle Jurassic volcanic rocks, occurring not only in the Lesser Xing' an-Zhangguangcai Ranges and western Liaoning Province, but also in the Manzhouli region, belong chemically to the high-k calc-alkaline series, implying the double subduction of MO oceanic plate and Farallon plate. Volcanic rocks of Late Jurassic mainly occur in the Great Xing' an Range (GXR), and a little in the Lesser Xing' an Range (LXR) and Zhangguangcai Range. The volcanic rocks in GXR which are trachyandesite and trachyte imply syn-collisional setting, and they were due to collisional orogeny accompanied the closure of MO Bay, and those in LXR and Zhangguangcai Range are intermediate-silicic rocks, which are formed under an extensional environment related to the deviation of Farallon plate. The most widespread volcanism in NE China was during in the early Early Cretaceous. Volcanic rocks largely distributed in GXR and around Songliao Basin are trachy-basaltic andesite, trachyandesite, andesite, trachyte and so on, which belong chemically to high-K calc-alkaline series and post-orogenic tectonic setting. The rocks formed during delamination of a thickened continental crust related to the post-orogenic diffuse extension due to the closure of MO suture bay. In the late Early Cretaceous, volcanism in GXR gradually decreased, whereas those in Songliao Basin increased. The volcanic rocks belong chemically to high-K calc-alkaline series and within plate setting, which formed under an extensional environment related to a backarc setting accompanied a low angle subduction of the Kula-Izanagi plate underneath the Eurasian continent. In the early Late Cretaceous, volcanic rocks were limited to the LXR and eastern Jilin-Heilongjiang provinces, and they are consist of medium-K calc-alkaline rocks such as basalt, basaltic andesite, andesite and dacite, implying active continental margin setting. Volcanism in early Late Cretaceous was affected by right-lateral strike-slip motions in continental margin in process of the oblique subduction of the Kula-Izanagi plate. Taking all this into account, we can conclude that the Mesozoic volcanism in Northeast China was both controlled by the closure of MO Bay and subduction of Paleo-Pacific plate. Mesozoic volcanic rocks were tectonic overprint that MO regime transferred to the circum-Pacific regime.
A huge volume of Late Paleozoic to Early Mesozoic granitoids is located in the middle part of the Inner Mongolia, which constitutes a giant granitic belt trending EW. As a representative of those intrusions, the Damiao granitoid occurs in the northern portion of the Siziwangqi area, mainly composed of mid-coarse-grained granodiorite with abundant mafic microgranular enclaves (MMEs) occurring. The MMEs can provide important clues for genesis and evolvement of granites. Petrological, geochronological, mineralogical results about the MMEs and host granite are presented in this paper. Zircons from the granite give a LA-ICPMS mean UPb age of 265 ±7Ma (2σ), and biotite grains from MME yield a Rb-Sr isochron age of 253 ± 5Ma (MSWD =0. 85). MMEs generally show ellipsoidal shape, and minerals in microscope are characterized by igneous and disequilibrium texture, which are considered as important evidences for magma mixing. The plagioclase phenocrysts have low composition end member of the anorthite (An) in the core and rim, compared to that of the mantle, while the contents of MgO in biotite phenocryst core and rim are lower than that of the mantle, both of them show oscillatory zone in the mantle. The resembled oscillatory variations in composition of the plagioclase and biotite phenocrysts from MME indicate that the crystallization environment was changed, due to magma mixing. The major and trace element compositions of the host granite and MEEs also show evidence on their genesis of magma mixing. The Rb/Sr-K/Rb diagram indicates that the MEEs are neither products by mineral fractional crystallization nor biotite accumulation. The Ce/Pb versus Ce and Ba, P2O5 versus δEu diagrams together with other trace elements bivariate ratio diagrams, imply that MMEs were generated by magma mixing, evidently consistent with their physical and chemical conditions. Geochemistry of the Damiao granodiorite is different from TTG or subduction-related Adakites. Underplating and magma mixing is a dominated mechanism for generation of the granite. In addition, the mineral chemistry and geochemistry indicate that the Damiao granodiorite is likely to form in syn-collisional. environment.
The Taipinggou porphyry molybdenum deposit was recently discovered in the Da Hinggan Mountain, China. Our geochronological study of ore-bearing porphyries and orebodies yields a K-feldspar40 Ar-39 Ar isochron age of 127. 5 ±4Ma for the ore-bearing, altered adamellite porphyry, a SHRIMP zircon U-Pb age of 131. 5 ± 1. 1Ma for the ore-bearing granite porphyry, and a molybdeniteRe-Os isochron age of 129.4 ±3.9Ma for the orebodies. This suggests that the molybdenum mineralization occurred in a period of 131.5 - 127.5 Ma; and that the porphyries and ore systems formed coevally with the regional Yanshanian tectonomagmatic event in Early Cretaceous.
Huanggang tin-iron deposit. Inner Mongolia, is an important deposit of the South Daxinganling metallogenic belt LA-ICP-MS zircon U-Pb dating results show that the K-feldspar granite and granite-porphyry in the Huanggang rocks were formed at 136.7 ± 1.1 Ma and 136.8 ±0.57Ma, respectively. The Huanggang granites are characterized by SiO 2 content (66.81%∼77.39% ) , Al 2O 3content ( 11.33%∼14.54%) , and significant depletion of magnesium, high ALK (5.65% ∼10.67%) , the K 2O/Na 2O values format a range of 0.32 to 10.53, averaging 2.78. The chondrite-nomalized REE pattern shows LREE enrichment, strong negative Eu anomalies, and δEu at 0.03 to 0.20. The high field strength elements such as Zr, Hf and lithophile elements such as Rb, U and Th are enriched, whereas the elements P, Ti, Ba and Sr are significantly depleted and their have similar Y/Nb values ( > 1.2) to those of oceanic island basalts. These features are coincident with the typical A1 within-plate anorogenic granite. Its genesis might be ascribed to the underplating of the mantle-derived magma which caused younger crust partial melting to form granitic magma within the lithosphère extension environment, and its magma source are related to the crust-mantle mixed remelting.
The Banlashan molybdenum deposit, located in the northern segment of Xilamulun molybdenum metallogenic belt, is a newly found medium porphyry molybdenum deposit. Zircon LA-ICP-MS U-Pb dating gives that ore-forming granodiorite porphyry was emplaced with age of 133. 5 ± 1. 7Ma. Therefore, the Banlashan molybdenum deposit was formed after 133Ma, in the Early Cretaceous. The wall rock- rhyolite porphyry was emplaced with age of 160 ±2Ma, earlier than the ore-forming age 27Ma at least. Hf isotope analyses for the rhyolite porphyry and granodiorite porphyry gives positive C 111 (t) values, which suggest that the source materials of two types of rocks come from newly accreted crustal materials. Besides the isotope similarity between rhyolite porphyry and granodiorite porphyry, they also resembled in the geochemical features, which is presented by high Al and K contents, low Mg, Ca and TFe contents, belonging to high K and cal-alkaline series ; and they are both enriched in LREEs and LILEs, such as Rb, Ba and Th, and depleted in HFSEs, such as Nb, Ta and Zr. However, the main differences between them are that XREE and europium depletion of rhyolite porphyry are higher than those of granodiorite porphyry, and that rhyolite porphyry is low Sr and high Yb ( Sr = 37.3×10-6 , Yb =4.81×10-6 ) , but granodiorite porphyry is high Sr and low Yb ( Sr = 628 × 10 -6, Yb = 1.64 × 10-6 ). All the features mentioned above indicate that rhyolite porphyry is probably derived from medium and upper crust, while granodiorite porphyry is the product of melting thicken lower crust. The source regions of the two types of rocks were deepening during the strong extension of lithosphere.
In this paper, the geochemistry and zircon U-Pb isotope chronology of the Chaihe K-feldspar granites in the central Greater Xing'an Range is studied and their petrogenesis and tectonic significance are discussed. The zircons from Chaihe K-feldspar granites show oscillatory growth zonations of typical magmatic origin and high Th/U ratios (0. 52 ∼ 1. 33), indicating a magmatic origin for the zircons, and yielded a LA-ICP-MS U-Pb age of 133 ± 3Ma. The granites have high Si02 rare earth elements (REE), high fieldstrength elements (HFSE), and large ion lithophile elements (LILE) contents. The REE patterns are characterized by enrichment of LREEs relative to HREEs and distinct negative Eu anomalies in chondrite-normalized REE diagram, which is characterized by right oblique and "V"-shaped feature. These features suggest that the Chaihe K-feldspar granites belong to aluminous A-type granite which derived from partial melting of crustal rocks with a typical character of A-type (rift valley or within plate) granite representing an extensional tectonic environment.
The Xilamulun metallogenic belt, located between Central Asian Orogenic Belt and North China Craton, is situated at the junction between the Paleo-Asian Ocean and the west Circum-Pacific tectonic regime. The ore belt was controlled by some tectonic systems, such as post-collisional extension of the Central Asian Orogenic Belt, Mongolia-Okhosk orogen, west Circum-Pacific tectonic and lithosphere large-scale thinning. Molybdenite Re-Os and zircon U-Pb dating of the Xilamulun ore belt show three periods of mineralizations which occurred at 260 -220Ma, 180 - 150Ma and 140 - 120Ma, respectively. Combined with the regional geology and geochemical study, we suggest that the mineralizations in the belt were formed during multiple geodynamic settings. The mineralization in 260 ~ 220Ma is probably related to a post-collisional extension stage with the generation of the porphyry molybdenum-copper deposits; The stage of 180 - 150Ma is related to a tectonic stress transformation from NS to EW; The large-scale mineralization occurred at 140 - 120Ma is related to the lithosphere thinning due to the upwelling of asthenosphere under the intra-continent extension. Based on geology and geochemistry of Mo-Cu deposits, authors suggest three ore-forming modes; i. e. "Chehugou" , "Jiguanshan" and "Aolunhua"-types. Study data show that ore-forming specialization are restricted by acid-alkali degree of host rock, magma source, oxygen fugacity of rock, evolvement fashion of magma and tectonic setting.
The Nianzigou Mo deposit, Inner Mongolia, is a recently discovered large-quartz veins type Mo deposit. Six samples of molybdenite for Re-Os isotopic dating are analyzed and the model ages obtained from 150.2 ± 2. 2 to 154.4 ± 2.2Ma, averaging 152.4 ± 1. 3Ma(2sigma;, MSWD = 1.6), and a good isochronic age of 154. 3 ± 3. 6Ma(2σ,MSWD = 1.9). It is indicated that the Nianzigou Mo deposit was formed in the Late Jurassic which belongs to the large-scale Yanshan molybdenum metallogenic period, and the tectonic settings are Mesozoic tectonic regime transformation of eastern China. The Re contents of the molybdenite are 12. 6 × 10-6 to 37. 0 × 10-6 , averaging 24. 9 × 10-6. According to the contents of Re in Nianzigou and contrasting with other molybdenum-bearing deposits, we consider the ore-forming materials of Nianzigou Mo deposit are derived from the crust-mantle mixed source and mainly from the crustal source.
Huanggang large tin-iron skarn deposit, Inner Mongolia, is located in the Huanggangliang-Ulanhot tin-lead-zinc-copper polymetallic belt, South Daxinganling. In this paper, five molybdenite samples separated from the Huanggang skarn ore bodies are used for Re-Os dating and obtained the model ages ranging from 134.6 ± 2.0 to 136.5 ± 1.9Ma, averaging 135.31 ± 0.85Ma. High Re content of molybdenite indicates that mantle fluid is involved in mineralization process. The mineralization of the Da Hinggan Mts area is mainly in Mesozoic Yanshanian, there are two ore-forming eruptive periods, i. e. , ca. 140 - 130Ma and 180 - 160Ma, while the tin-lead-zinc- copper-silver polymetallic deposits related with the small intrusion in Yanshanian under lithospheric extensional and thinning environment mainly occurred in ca. 140-130Ma; the molybdenum-lead-zinc-copper-aurum polymetallic deposits related with the postcollision orogeny of Siberia plate and North China plate in Early Yanshanian mainly occurred in ca. 180-160Ma. Huanggang tin-iron deposit is the product of large-scale mineralization under the paleo-Pacific plate subduction environment.
Based on petrological and geochemical studies, the Mesozoic granitoids out croppied in the northern marginal region of North China Craton can be grouped into five types: strongly peraluminos leucogranites, normal calc-alkaline and high-K calc-alkaline granites, high-Sr granites, alkali A-type granites, and peralkaline granites. They are very different not only in their geochemical features, but also in age of emplacement, petrogenesis and geodynamic environment. The peraluminous leucogranites were derived from dehydration melting of metapelites and metagreywackes during uplift and decompression of the thickened crusts without any mantle involvement in the early stage of post-collisional phase. The high-Sr granites were derived from the overthickened lower crust by dehydration melting of intermediate-acid igneous rocks and basaltic amphibolites. Both alkali granites and peralkaline granites were generated in the extensional regime of regional lithosphere, but the latter indicating a rifting event of intra-plate anorogenic setting. Based on the regional geological evolution and the sequential emplacement of the granitoids, it is suggested that these granitoids imagined a transition of geodynamic environments from post-collisional to intra-plate anorogenic. The strongly peraluminous leucogranites + calc-alkaline and high-K calc-alkaline granites + high-Sr granites + alkali A-type granites comprise the post-collisional granitic suite, while the peralkaline granites + alkali A-type granites constitute the intra-plate anorogenic granitic suite. The regional granitic magmatism distinctively indicates a significant switch of regional tectonics in between 160 ∼ 150 Ma in the Mesozoic. In the early-middle Mesozoic before 160 Ma, regional crust/lithosphere might undergo an early stage of post-collisional thickening processes, during which voluminous high-Sr granites and several strongly peraluminous leucogranites were emplaced: but during 150 ∼ 110 Ma, the regional crust/lithosphere experienced a late post-collisional stage of strongly extensional tectonics and crustal thinning, which is characterized by the onset of emplacement of alkali A-type granites, along with the high-Sr granites became markedly insignificant and eventually disappeared. At about 110 Ma typical pealkaline granites were emplaced without any high-Sr granitic magmatism, indicating that the regional crust had been thinned to normal thickness (38 ∼ 40 km) and intra-plate rifting began. It is believed that the "subduction-style" geochemical signatures of the post-collisional calc-alkaline and high-K calc-alkaline granites were inherited from the source regions that had been activated during the subduction and syn-collision stages of the Siberian plate subducting beneath the North China Craton.
Located in the western slope of central Da Hinggan Mountains, the Shamai pluton is an important parts of the Erlianhot-Dongwuqi granite belt, and has an outcrop area of about 2700km2. It is composed of fine- to medium-grained biotite granite. Many dike swarms and xenoliths were discovered in the pluton. Chemical analysis show that the granites have high SiO2 (73.55% ∼ 76.10%), moderate Al2O3 (12.86% ∼ 13.98%) and alkaline (Na2O + K2O = 6.46% ∼ 9.34%), low P2O5 (< 0.1%). They are slightly peraluminous, contain normative corundum (< 1%). It can be ascribed to the peraluminous S-type granite. Trace and rare earth elements of the granites are characterized by enriched in Rb, Th, U, Ta, and depleted in Ba, Sr, P, Ti. Chondrite-normalized REE patterns display significant negative Eu anomalies (δEu = 0.02 ∼ 0.13). The characteristics of the trace and REE elements of the granite suggest that it has been experienced highly fractional crystallization. The granites have broad Nd isotopic composition with initial εNd values ranging from -1.67 to 7.80, and young two-stage depleted-mantle model ages (T2DM = 275.79 ∼ 1048.41Ma). Based on field geological investigations, combined the geochemical characteristics with the regional tectonic settings, it is suggested that the Shamai pluton was formed in the late Mesozoic post-collision stage in which a rapid lithospheric extension must have occurred, resulting in the underplating of the basaltic magma. The crust-mantle miscible magma induced by the underplating assimilated the upper crust and fractional crystallized (AFC) during ascending at the same time, and finally intruded the Middle-Lower Jurassic volcanic-sedimentary rocks and formed the Shamai pluton.
The costal area of the Yangtze River in Anhui Province situated in the middle segment of the Yangtze River Deep Fault Belt is structurally located in the foreland of the Dabie Orogenic Belt. In this area are widely exposed a set of post-collisional to postorogenic associations of volcanic-intrusive complexes formed by two episodes of magmatic activities in the post-collisional to postorogenic regimes and corresponding crustal interaction with mantle occurring in the Late Jurassic to Early Cretaceous. The post-collisional magmatic activity took place in the setting of lithospheric extension and thinning at about 125 ∼ 145 Ma. Its beginning and end are remarked by formation of gabbroic xenoliths and pyroxene cumulates in intrusions in Tongling and alkalis-rich magmatic rocks along either bank of the Yangtze River, respectively. The association formed in this episode includes peraluminous silicic rocks and metaluminous mafic-felsic igneous suites, ranging from medium- to high-K calc-alkaline to shoshonitic. The peraluminous silicic rocks include volcanic rocks of the Zhongfencun and Chisha Formations in the Fanchang Basin (FB) and intrusions distributed from Guichi to Xuanzhou. The medium- to high-K calc-alkaline suite consists mainly of intermediate-acidic intrusive rocks in Tongling and those distributed from Chuxian to Shaxi, and the shoshonitic suite is composed of intermediate-basic intrusions in Tongling, alkalis-rich magmatic rocks distributed along either bank of the Yangtze River and volcanic rocks of the Longmenyuan and Zhuanqiao Formations in the Lujiang-Zongyang Basin (LZB) and the longwangshan and Dawangshan Formations in the Nanjing-Wuhu Basin (NWB). The postorogenic magmatic activity occurred in the background of lithospheric delamination at about 105 ∼ 125 Ma. Its beginning and end are remarked by formation of gabbro with spinel lherzolite xenoliths in NWB and phonolite with feldspathoid phenocrysts in NWB and LZB, respectively. The association formed in this episode ranges from alkaline to peralkaline. The alkaline suite consists mainly of intrusive rocks with gabbroic composition in NWB and volcanic rocks of the Kedoushan Formation with garnet in FB and the Shuangmiao Formation in LZB, and the peralkaline suite is composed of volcanic rocks of the Fushan Formation in LZB and the Niangniangshan Formation in NWB. There are two episodes of crustal interaction with mantle corresponding to the two episodes of post-collisional to postorogenic magmatic activities. The first episode occurred as intensive interaction of middle to lower crust with underplated basaltic magma derived from upper portion of lithosphere mantle, while the second episode existed as slight interaction of middle to lower crust with basaltic magma derived from lower portion of lithosphere mantle.
Located in the southern segment of the Da Hinggan Mountains, the Aolunhua Mo deposit is newly found as a porphyry molybdenum deposit to the north of the Xilamulun fault. U-Pb dating for zircons from the Aolunhua granitic porphyry by SHRIMP method yields an age of 134 ± 4Ma. Re-Os isotopic dating by the ICP-MS method on molybdenites separated from the Aolunhua molybdenum deposit yields an isochron age of 132 ± 1Ma (MSWD = 1. 12), with model ages ranging from 131 ±2 to 133 ± 2Ma. The ore-forming time of the porphyry Mo deposit represented by the Re-Os isochron age is almost same as the time of petrogenesis, both in early Cretaceous. Our new age data, along with the published age data of the polymetallic deposits in the Xilamulun metallogenic belt, lead us to suggest that 130 - 150Ma is the main period of ore-formation in this area, and the ore-forming material for the deposits on both sides of the Xilamulun fault were from different sources. The unique metallogenic characteristics of the polymetallic deposits in the Xilamulun metallogenic belt was probably linked to the composite evolution of the Paleoasian and west circum-Pacific tectono-magmatic domains. The main metallogenic pulse formed responding to the intensive magmatism and minerogenesis in early Cretaceous during which an extensional back-arc regime was developed in the Xilamulun area following accretionary orogenesis and thickening of continental crust.
Derbugan fault zone, a NE tending fault zone in the West of the Great Xing' an Range uplift and along the western margin of the Hailar-Labudalin-Genhe basins, is the famous zone which is the NS boundary fault zone of the Derbugan metallogenic belt. In order to understanding the character for the activity and timing of this fault, and its relations to the Hailar-Labudalin-Genhe basins, and polymetal ore deposit along this fault, we show the SHRIMP zircon and mica 40Ar/39Ar dating for the granule-biotite granitic vein, granodioritic gneiss with ductile deformation and mica-quartz schist in this fault zone. SHRIMP zircon U-Pb dating of the granodioritic gneiss yield concordant age of 300. 6 ±9. 3Ma, together with its igneous zircon in CL image, indicate that age of 300. 6 ±9. 3Ma is the protolith ages for this gneiss. The biotite 40Ar/39Ar dating also from this granodioritic gneiss, which yield the plateau age of 130. 9 ± 1. 4Ma, together with the biotite 40Ar/39 Ar plateau age of 115. 6 ± 1. 6Ma from the mica-quartz schist, indicate that those ages between the 115 ∼130Ma are the extensional event ages at the Early Cretaceous in the Derbugan fault zone. The granule-biotite granitic vein also analyzed by the SHRIMP method, which yield the concordant age of 130. 1 ±1. 4Ma with the igneous zircon in CL image, indicate that age of 130. 1 ± 1.4Ma are the protolith age and incursion due to the syn-extensional event during the Yanshanian in this fault zone. Those results from this study, suggest that the Derbugan fault zone is the youngest extensional structure with the ages between 110∼130Ma during the Yanshanian in this area. Derbugan fault zone has dominated the framework of the Mesozoic volcanism in the Hailar-Labudalin-Genhe basins, the crust evolutions and ore-forming types in the Great Xing'an Range. Therefore the Derbugan fault zone with the extensional event ages of 115∼130Ma are the typical evidence for the intra-continental orogen at Yanshanian during the Mesozoic.
The age of single zircon is thought to he the recording of single tectonic, magmatic or metamorphism activity, the ages ol a large amount of zircons got from different types of primary rocks should be able to indicate the geotectonic evolution history. The authors of the paper collected 2636 zircon ages detemiined by U-Pb dating from 123 samples in middle-northern Daxinganling, dated by authors or gatherd from published data, the statistics on these data has shown that ihe zircon ages have several peak value ages of 840 ∼780Ma, 530 ∼ 440Ma, 330 ∼280Ma, 240 ∼ 190Ma, 180 ∼ 160Ma and 150 ∼ 120Ma, and three blank time space of >840Ma, 770 ∼540Ma, 440 ∼400Ma. The ages of different types zircons generated by magmatism, metamorphism, or that inherited from former rocks have similar statistics features. The peak value of zircon ages has a good accordance with the time that important tectonic event look place in middle-northern Daxinganling Mountains, such as, the formation of basement, mircoplate subduction and collision. The blank period of zircon ages is corresponded to that of ocean spread or passive continental margin event. It is concluded that a large amount of zircon ages determined by U-Pb dating method for primary rocks also can be applied to study the geotectonic evolution history, just like the zircon ages from rivers detrita. Study on the statistics on zircon ages, granite association and tetanies indicates a very complicated tectonic evolution history has been taken place in middle-northern Daxinganling Mountain, that is, the formation of basement in Plaeoprolozoic, growth ol continental crust in Neoprotozoic, breakdown ol plate in the end of Neoprolozoic, subdution, spreading, accretion and collision between miroplales in Paleozoic, continental collision in Early Mesozoic, poslorogenic extension and collapse in Late Mesozoic related to the Mongolia - Okhotsk orogeny and continental marginal tectonic-magmatic event related to the subdution of West Pacific Ocean in Mesozoic. The study has also shown that the Mongol-Okhostsk Ocecn has been closed in Late Triassic Period in Transbakal area. There is a large amount ol granites, migmatiles related to continental collision, and metaomorphic complex, basin-range, continental bimodal volcanic rocks related to poslorogenic collapse, occurred in middle-northern Daxinganling. It is suggesting that the geodynamic background for the polymetal mineralizaton in the area need to be reconsidered.
The Late Jurassic Longgouhe and Ershiyizhan intrusions, located in the Upper Heilongjiang Basin of northern Da Hinggan Mountains, are closely related to the porphyry Cu-Au mineralizations.. The intrusions are mainly composed of quartz diorite, quartz monzodiorite and granodiorite. Most of them are the rocks of high-K calc-alkaline series, with minor of shoshonite series. Their SiO2 and Al2O3 contents range 61.37% - 66.59% and 15.35% - 17.06%, respectively. The MgO content ranges 2.02% - 3.47%, with a high Mg# index ranging from 44 to 59. The (La/Yb)N and δEu values range from 16.85 to 81.73 and from 0.68 to 0.93, respectively, showing strongly fractionated REE patterns that are similar to those of adakites. The rocks are enriched in Ba, Sr and LREE, but strongly depleted in Nb and Ta, and slightly depleted in Rb and Ti. The Yb and Y contents span of 0.31 - 1.32 μg/g and 4.32 - 12.07 μg/g, respectively, suggesting that the rocks are depleted in Yb and Y. The Sr /Y ratios are between 67.74 and 220.60, showing a clear feature of low-Y and high-Sr. All these geochemical characteristics are similar to adakites. Considering that the Paleo-Asian Ocean and Mongol-Okhotsk Ocean were closed in the Late Paleozoic and Permian-Middle Jurassic, respectively, the origin of the interested adakites can be related to partial melting of delaminated crust which were thickened by the collisional orogeny between the Siberia and Mongol-Sinokorea continents.
The southern Great Xing’an Range (SGXR), located in the southeastern part of Inner Mongolia, China, shows intense Mesozoic tectono-magmatic activity and hosts economically important polymetallic (Cu–Pb–Zn–Sn–Fe–Ag–Au–Mo) mineralization. Here, we present new zircon U–Pb ages, whole-rock geochemical data, Nd–Sr–Hf isotopic data and Re–Os ages for the Taibudai deposit in the SGXR. The Taibudai granitoids show high SiO2 (70.62–72.13 wt.%) and alkali (Na2O + K2O = 7.04–8.60 wt.%) concentrations, low MgO (0.89–1.37 wt.%) and Al2O3 (∼14 wt.%), ASI ratios <1.1 (0.94–0.97), LILEs (e.g., Rb) enriched, HFSEs (e.g., Nb, Ta, Ti, and P) depleted, and have low Sr and Yb concentrations, classifying these rocks as fractionated I-type granites. The Taibudai granitoids have negative εNd (t) values ranging from −2.2 to −1.6 and relatively low initial 87Sr/86Sr ratios from 0.70536 to 0.70581. In situ Hf isotopic analyses on zircons using LA–MC–ICP–MS show variable positive εHf (t) values ranging from +0.80 to +13.55, corresponding to relatively young two-stage Hf model ages from 801 to 942 Ma (excluding one spot). These mineralogical, geochemical, and isotopic features strongly suggest that the primary magmas of the Taibudai granitoids were derived mainly from the partial remelting of Neoproterozoic juvenile crustal material, with no remarkable modification through incorporation of continental or subduction-related material. Re–Os isotope analyses of molybdenite from the deposit yield an ore-forming age of 137.1 ± 1.4 Ma. Re contents range from 4.37 to 41.77 ppm, implying ore material components have a mixed crust–mantle origin. SHRIMP analysis of zircons show that the monzogranitic porphyry and biotite granite in the Taibudai deposit were formed at 137.0 ± 0.9 Ma and 138.3 ± 0.9 Ma, respectively, indicating a temporal link between granitic magmatism and Cu mineralization. This result, combined with the regional geology, tectonic evolution, and age data from the literature, suggests that the Early Cretaceous (∼140 Ma) was the peak metallogenic epoch for the Great Xing’an Range, and the mineralization in this period generally takes the form of porphyry, skarn, or hydrothermal polymetallic ore deposits in an active extensional continental margin environment. The Taibudai porphyry and associated mineralization provides a typical example of magmatism and metallogeny associated with a Paleo-Pacific plate subduction, continental margin, back-arc extensional setting.
The East Luoguhe intrusion in Mohe County, Heilongjiang Province, located in the northern end of the Great Hinggan Range, is mainly composed of monzogranite-porphyry, syenogranite-porphyry and quartz monzonite-porphyry, with minor dioritic microgranular enclave. The intrusion belongs to I-type granite, with affinity to high-K calc-alkaline series. The SHRIMP zircon U-Pb age of the granite-porphyry is 129. 8 ±2. 2Ma, indicating that the intrusion formed in Early Cretaceous. Its SiO2 and Al2O3 contents range 68. 03% -74. 32% and 13. 06% -14. 55% , respectively. The Na 2O/K2O ratios range 0. 45 - 0. 86, ASI values from 0. 94 to 1. 11 ( mostly <1. 1) , and the Mg* index from 18 to 42( mostly < 30). The REE content is between 160.00 x 10-6and235. 15 x 10 -6, with δEu of 0. 31 - 0. 52 ( average 0. 41 ) and ( La/Yb ) N ratios of 8. 99 - 17. 87 ( average 13. 82 ) . The East Luoguhe intrusion is characterized by low-Sr (118 x 10 -6 -268 x 10 -6) , high-Y ( 16. 9 x10-6-26. 1 x 10 -6, generally >18 x10-6), and low Sr/Y ratios (5. 62-13. 81). The intrusion is enriched in Rb, Th, U, K, Zr, Hf and LREE (e. g. La, Ce, Nd and Sm) , but strongly depleted in Ba, Sr, P and Ti, with notable depletion of Nb and Ta. The geochemical signatures above are similar to those of post-collisional granitoids, suggesting that the East Luoguhe intrusion can be classified into the group of post-collisional granites. The intrusion has low initial 87Sr/86 Sr ratio ( 0. 702486 - 0. 707269, average 0. 705434 ) , clear negative εND ( t) value ( -3.45 - -2.64, average - 3. 01 ) , young Nd-model age (969 - 1131Ma, average 1018Ma) , and extremely low δ18O ratio ( - 8. 1%o to 4. 1%o for K-feldspar). And the 206Pb/204 Pb ( 18. 5939 - 18. 6721, average 18. 6426 ) , 207Pb/204 Pb ( 15. 6019 15.6058, average 15. 6035) and 208Pb/204Pb (38. 4058 -38. 5249, average 38. 4613 ) ratios for K-feldspar are relatively high. The Nd-Sr-Pb-O isotope systematics shows that the intrusion originated from partial melting of a source with remarkable mantle-derived components. The source is likely the juvenile crust formed during the convergence of Rodinia supercontinent at the transition from Mesoproterozoic to Neoproterozoic. Given that the Paleo-Asian Ocean was finally closed at the end of Late Paleozoic, followed by closing of the Mongol-Okhotsk Ocean during Permian-Middle Jurassic, the East Luoguhe intrusion of Early Cretaceous age must be formed in the collision regime between the Siberia and Mongol-Sinokorea continents, especially in a tectonic transition setting from compression to extension.
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