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Analysis of forty-two major and trace elements in USGS and NIST SRM glasses by LA-ICPMS

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... Analysis of USGS glass standards (BCR-2G, BHVO-2G, and BIR-1G) indicates precision and accuracy both better than 10% for La, Ce and Pr and better than 14% for other REEs. Analytical details and analyses of the USGS and NIST SRM glass standards have been reported elsewhere [37] . ...
... For example, T-Grt-3-2r indicates the second analysis on the rim of garnet 2. Fig. 2. Chondrite-normalized rare earth element distributions of garnets from Shuanghe eclogite SH02. The line LOD indicates the limit of the detection for LA-ICP-MS analysis at Northwest University [37] . Chondrite normalizing values are from Taylor and McLennan [32] . ...
... For comparison, results obtained at Laboratory of Inorganic Chemistry, ETH, Zürich are shown as dash lines. The line LOD indicates the limit of detection for LA-ICP-MS analysis at Northwest University [37] . Chondrite normalizing values are from Taylor and McLennan [32] . ...
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In-situ excimer laser ICP-MS analysis of minerals of eclogites and garnet pyrox-enites from type localities (Shuanghe, Maowu, Bixiling, and Yangkou) in the Dabie-Sulu ultra-high-pressure metamorphic belt reveals highly variable Ce anomalies from negative to positive in garnet. Similar Ce anomalies are also present in omphacite or clinopyroxene but to a much lesser extent. Such mixed negative and positive Ce anomalies mimic those found in severe weathering profiles developed under oxidizing conditions. They suggest the presence of subducted sediment components in the eclogites and garnet pyroxenites, which in turn points to the potential importance of the recycled sediments in modification of the mantle composition during the deep subduction of the continental crust.
... The LA-ICP-MS for zircon in situ U-Pb dating consists of an ICP-MS (Elan 6100DRC) and an excimer laser ablation system (193 nm,GeoLas 200M,Lambda Physics). This combination has lower elemental fractionation than other kinds of laser ablation systems, such as 266 and 213 nm Nd: YAG laser system (Gao et al. 2002;Guillong et al. 2003), which is important for zircon U-Pb dating. The spot sizes applied were 30-40 mm in diameter. ...
... 204 Pb signals of zircons are generally not statistically significant. Detailed instrumentation and analytic accuracy descriptions are similar to those in the literature (Xing and Xu 1999;Gao et al. 2002;Yuan et al. 2003Yuan et al. , 2004Wang et al. 2006). The time-resolved spectra were processed off-line using Glitter software (ver 4.0, Macquarie University) to calculate the isotopic ratios. ...
... The LA-ICP-MS for zircon in situ U-Pb dating consists of an ICP-MS (Elan 6100DRC) and an excimer laser ablation system (193 nm,GeoLas 200M,Lambda Physics). This combination has lower elemental fractionation than other kinds of laser ablation systems, such as 266 and 213 nm Nd: YAG laser system (Gao et al. 2002;Guillong et al. 2003), which is important for zircon U-Pb dating. The spot sizes applied were 30-40 mm in diameter. ...
... 204 Pb signals of zircons are generally not statistically significant. Detailed instrumentation and analytic accuracy descriptions are similar to those in the literature (Xing and Xu 1999;Gao et al. 2002;Yuan et al. 2003Yuan et al. , 2004Wang et al. 2006). The time-resolved spectra were processed off-line using Glitter software (ver 4.0, Macquarie University) to calculate the isotopic ratios. ...
Article
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The Tongling district is one of the most important non‐ferrous metal producers in China. The origin of Cu–Au deposits in the region is closely related to Late Mesozoic intermediate intrusions, which are mainly high‐K calc‐alkaline and shoshonitic series. Geochemical characteristics indicate that these granitic rocks are mixtures of more than two compositional end‐members, i.e. mantle‐derived melts and crust components incorporated through assimilation. Three important magmatic intrusions related to the Cu–Au deposits in the Tongling region – the Jiguanshi quartz monzodiorite, the Xishizishan quartz diorite and the Miaojia diorite porphyry – were selected for this study. Zircon U–Pb dating by LA ICP‐MS yielded two groups of ages (130–132 and 138–140 Ma) for these intrusions. Pyrite Re–Os age for the Xinqiao Cu–Fe–S deposit in the Tongling region is 126±11 Ma. Trace elements of zircon grains show that the earlier Cu–Au mineralization event was associated with adakitic rocks characterized by high positive Ce anomalies, produced at an elevated oxygen fugacity range. In contrast, later iron‐sulphur mineralization was closely related to low positive Ce anomalies, reflecting low oxygen fugacities. Considering that Pacific lithospheric subduction was the dominant factor that controlled major tectonic evolution in eastern China during the Early Cretaceous, the geochemical characteristics of these coeval ore‐forming intermediate intrusive rocks in the Tongling district were likely the result of Pacific plate underflow.
... They are obscured to the north by unconformably overlying Early Permian clastic sedimentary rocks, and bounded to the southwest by the ductile fault that separates them from Silurian strata (Figure 1). Brief descriptions of the volcanic rocks cross-section ( Figure 2), in approximate east to west progression, as well as the sampling locations, are as follows: At the first sites, Early-Middle Permian meta-sandstones with a blastopsammitic texture and medium-bedded structure with weak deformation and at lower greenschist facies grade overlie chlorite albite schists with sericite quartz schist intercalations ( 17), and an altered diabase sill (site 16) and dike (site 18). At sites from 20 to 28, there are greenschist and gabbro-diabase occurring as interlayers. ...
... For the detailed analytical procedures, operating techniques and data reduction refer to refs. [17][18][19]. ...
Article
In the Dabudaer region of the Tianshuihai Massif (Xinjiang, Northwest China), metavolcanic rocks within the mainly meta-sedimentary Bulunkuoler Group are basalt, basaltic andesite, and rhyolite. In situ zircon U-Pb LA-ICP-MS dating on rhyolite magmatic zircons yielded an age of 2481±14 Ma, interpreted as the eruption age of the Bulunkuoler Group volcanic rocks. The basalt and basaltic andesite are low-Al tholeiite series and the rhyolite is low-Al calc-alkaline series. All of rocks are characterized by enrichment of LREE and LILE (Rb, Th and Ba), depletion of P, Nb, Ta and Ti, and absence of Eu anomalies. The ε Nd(t) of basalts ranges from 3.14 to 4.88 indicating a depleted mantle source. The trace element signatures show that these magmas experienced intense crustal contamination during their ascent. Direct evidence for crustal contamination is the xenocrystic zircons in the ryholite, with ages back to ca. 3300 Ma. The primitive-mantle normalized and Zr/Y-Zr diagrams for the basic volcanic rocks show that they formed in an intra-continental tectonic setting. Combined with the previous studies and compared with North China Craton Neoarchean basic volcanic rocks, it is supposed that the Bulunkuoler Group volcanic rocks reflect the Palaeoproterozoic mantle magma underplating and interaction with felsic crust.
... The analytical precision for major elements is better than 5%. The detailed sample-digestion procedure for ICP-MS analyses and analytical precision and accuracy for trace elements were as described by Gao et al. (2003). ...
Article
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A discrete belt of Albian−Cenomanian granitoid plutons occurs in the Lhasa and Qiangtang terranes in the Central (CTP) and Eastern Tibetan Plateau (ETP) and represents a major magmatic pulse in the plateau’s crustal evolution during the Cretaceous. The geochemistry, petrogenesis, and magmatic development of these granitoids are different from those of magmatic arc granitoids along the southern edges of the Lhasa and Qiangtang terranes, indicating different heat and melt sources and tectonic setting of their formation. We present here new mineral, whole-rock and isotope geochemistry, and zircon U-Pb age data from the Xiasai pluton in the ETP and discuss its geochemical-petrological characteristics and magmatic development in comparison to the other Cretaceous plutons in the ETP and CTP, and within the tectonic framework of the Mesotethyan geology of Tibet. Zircons from the Xiasai and other plutons in the ETP have yielded U-Pb ages ranging from 106 Ma to 93 Ma in comparison to 115 Ma and 100.3 Ma zircons from the Southern Qiangtang Terrane (SQT) and 113.4 Ma and 109 Ma zircons from the Northern Lhasa Terrane (NLT) farther west. The Cretaceous granitoids in the ETP and CTP range in composition from granite, K-feldspar granite to monzogranite and biotite monzogranite, representing highly fractionated I-type granites with relatively high SiO2 and K2O contents, variable (Na2O + K2O)/CaO and FeOT/MgO ratios, and (Zr + Nb + Ce + Y) abundances. They display significant negative Eu anomalies (Eu/*Eu) = 0.04−0.12) and strong depletions in Sr and Ba, and are strongly enriched in large ion lithophile elements but depleted in high field strength elements. Their εHf(t) values correspond to wide ranging Hf isotope crustal model ages (TDMC) of 0.3−1.9 Ga, and their Sr-Nd isotopic signatures show elevated (87Sr/86Sr)i ratios (0.7034−0.7105) and negative εNd(t) values of −8.8 to −4.9. These high whole-rock (87Sr/86Sr)i ratios and relatively high Th/Nb and Th/Yb ratios indicate incorporation of melts derived from partial melting of subducted sediments into the melt evolution of these granitoids that involved partial melting of the subduction-metasomatized lithospheric mantle and the mafic- to intermediate-composition continental crust. The extant zircon crystallization ages of the granitoid intrusions in the CTP and ETP show eastward younging of their emplacement from 115 Ma to 93 Ma, suggesting an apparent eastward migration of the heat source through time. A diachronous collision of the NLT with the SQT during 145−120 Ma and the subsequent slab breakoff induced, eastward propagated slab tear and asthenospheric upwelling produced the hybrid melts of the Albian−Cenomanian granitoids and their emplacement in a discrete, narrow magmatic belt in the CTP and ETP.
... The sample preparation method is described in Darbandi et al. (2020). The analytical procedure is performed according to the analytical procedures described by Gao et al. (2003). The detection limits for the elements are presented in Table 2. ...
Article
The Mehdiabad zinc-lead deposit is one of the well-known deposits in the Central Iran structural zone, however, the genesis of the deposit is still controversial. The host rock of the ore is dolomitic limestone of the Lower Cretaceous Taft Formation. In the two main orebodies of the deposit, which includes the Black Hill and the East Ridge ore zones, the oxide and sulfide ores are observed at the surface and depth, respectively. The elements Zn, Fe, Mn, and Mg are more abundant in the East Ridge ore zone (in both sulfide and oxide ores), and Ba, Pb, Ag, and Cu are more abundant in the Black Hill oxide ore. Based on the distribution of elements and their correlation with each other in these ore zones, the elements are divided into three general groups of terrigenous elements, chemically-deposited elements, and ore-forming (hydrothermally deposited) elements, which is supported by the results of factor analyses. The spatial distribution of elements is jointly affected by the contact of host rocks, the boundary of oxide-sulfide ores, and fault zones. The main factors governing the distribution of elements are the mechanical transfer of detrital sediments, chemical sedimentation, transfer by hydrothermal fluids, oxidation, and surface dissolution, which affected the spatial distribution of elements. The ore-forming elements are mostly affected by hydrothermal fluids and oxidation. This study not only provides additional information about the genesis of Mehdiabad deposit but also could help the exploitation of ore and further exploration purposes. The results of this study can help the exploration and exploitation of the Mehdiabad deposit and similar deposits in the region.
... The trace elements were tested by Nanjing University using HR-ICPMS. The detailed process has been described by Gao et al. (2003). ...
Article
The Huogeqi deposit is a major Cu-Fe-Pb-Zn deposit in China. Numerous studies have been conducted on the genesis of Cu-Pb-Zn sulfides of this deposit; but detailed researches on the genesis of magnetite ore bodies and its relationship to sulfide ores are few. This study utilizes field and microscopic techniques to showcase the hy-drothermal characteristics of magnetite ore and tremolite rocks, including net-veined magnetite ore, which cuts across carbonate rock and quartzite, and intrusive contacts between magnetite-bearing tremolite rocks and quartzite, carbonaceous slate, and carbonate rock. Furthermore, calcite with metasomatic relict texture could be widely observed near magnetite and tremolite. Magnetite-bearing tremolite rocks with low contents of trace elements, rare earth elements, and obvious positive anomalies of Eu differed from the mica schist and carbo-naceous slate, but were consistent with the carbonate rocks, revealing that the magnetite ore and tremolite rocks have a hydrothermal origin and are closely related to carbonate rocks. The Fe isotopic compositions of 22 magnetite and 17 wall samples were determined using MC-ICP-MS methods. δ 56 Fe values of magnetite-bearing tremolite rocks varied from − 0.57 to − 0.15‰ (average, − 0.38‰), which differed from those of the mica schist (0.27-0.33‰), quartzite (− 0.12 to 0.57‰), and carbonaceous slate (0.30-0.38‰), but were similar to the car-bonate rocks (− 0.38 to − 0.51‰). δ 56 Fe values of magnetite varied from − 0.48 to 0.36‰ (average, − 0.11‰), which differed from banded-iron formation and magmatic magnetite deposits but were like skarn deposits. The δ 56 Fe value of the initial ore-forming fluid was − 0.09‰ at 350 • C, which is consistent with the fluid that likely originated from the fluid exsolution of granite. According to theoretical calculations, δ 56 Fe values of the residual fluid after precipitation of magnetite ores ranged from − 1.01 to − 0.94‰, and that for pyrite precipitation ranged from − 0.02 to 0.07‰, which is consistent with the measured Fe isotopic data of pyrite. Hence, we suggest that the hydrothermal magnetite and Cu-Pb-Zn sulfides of the Huogeqi skarn deposit could be derived from similar hydrothermal fluids.
... After digestion, the clear solutions were treated with HClO4 to remove HF. The analytical procedure is performed according the analytical procedures described by Gao et al. (2003). The detection limit for major elements by XRF is 0.01% and for trace elements by ICP-MS is 0.02-1 ppm, depending on the element. ...
Article
Shahrak iron deposit is located at the north of Sheikh-Besharat village, northwest of the city Hassan-Abad Yasukand, Kurdistan province. The study area includes igneous rocks, skarn zone, metamorphic zone (marble), and iron ore. Igneous rocks exposed in the district include calc-alkaline volcanic rocks with the dominant composition of rhyolite, andesite, dacite, trachyandesite, volcanoclastic (tuff) and intrusive rocks of diorite and granodiorite type, and carbonate rocks of Qom Formation (Miocene). Based on field studies, petrography of volcanic rocks and the skarn zone and Fe ore mineralography in the area, it can be said that iron mineralization and skarn formation occur adjacent to the igneous masses. The skarn index minerals are evidence of this event. The spider diagram patterns of rare earth elements of the Shahrak deposit samples normalized to the chondrite indicate more enrichment in light rare earth elements (LREE) than heavy rare earth elements (HREE). Positive Eu and negative Ce anomalies are characteristic of hydrothermal iron ore deposits. The different pattern of trace elements in the igneous rocks and the ore indicates their various geneses. The less important role of low salinity non-magmatic fluids in ore formation is concluded by chemical analysis results.
... Determination of the trace element compositions was carried out on a PerkinElmer Sciex ELAN DRC-e ICP-MS, with data accuracy better than 5%-10%. The instrument parameters and detailed analytical techniques are given in Gao et al. (2007). ...
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Identifying the crust-mantle interactions in association with the evolution of the Precambrian microcontinents provides critical constraints on the accretionary evolution in the Central Asian Orogenic Belt (CAOB). The Bainaimiao arc terrane (BAT) is one of the most important Precambrian microcontinents in southeastern CAOB, however, few studies have paid attention to the types and the evolving processes of the crust-mantle interactions that occurred before its final accretion onto the northern North China carton. This study presents an integrated study of geochronology, zircon Hf isotope and whole-rock geochemistry on the latest Neoproterozoic diabases and the Early Paleozoic arc intrusions in the western BAT. The latest Neoproterozoic (ca. 546 Ma) diabases display low SiO2 (46.52–49.24 wt.%) with high MgO (8.23–14.41 wt.%), Cr (66–542 ppm) and Ni (50–129 ppm), consisting with mantle origin. Their highly negative zircon εHf(t) (−12.0 to −24.7) and high Fe/Mn ratios (62.1–81.7) further indicate a significantly enriched mantle source. Considering that the BAT maybe initially separated from the Tarim craton with a thickened crustal root, we propose that these diabases were generated through partial melting of an enriched lithospheric mantle source that had been hybridized by lower-crustal eclogites during foundering of the BAT lower crust. The Early Paleozoic (ca. 475–417 Ma) arc intrusions in western BAT can be divided into Periods I and II at approximately 450 Ma. The Period I (>450 Ma) intrusions contain abundant mafic minerals like hornblende and pyroxene, and show positive zircon εHf(t) (+1.5 to +10.9). They are predominantly medium-K calc-alkaline with broad correlations of SiO2 versus various major and trace elements, which correlate well with the experimental melts produced by the fractional crystallization of primitive hydrous arc magmas at 7 kbar. We assume they were formed through mid-crustal differentiation of the mantle wedge-derived hydrous basaltic melts. By contrast, the Period II (≤450 Ma) intrusions are characterized by variable zircon εHf(t) (−15.0 to +11.5) with irregular variations in most major and trace elements, which are more akin to the arc magmas generated in an open system. The general occurrence of elder inherited zircons, along with the relatively high Mg# (>45) of some samples, call upon a derivation from the reworking of the previously subduction-modified BAT lower crust with the input of mantle-derived mafic components. In combination with the Early Paleozoic tectonic mélanges flanking western BAT, we infer that the compositional transition from Period I to II can be attributed to the tectonic transition from south-dipping subduction of Solonker ocean to north-dipping subduction of South Bainaimiao ocean in southeastern CAOB. The above results shed light not only on the latest Neoproterozoic to Early Paleozoic multiple crust-mantle interactions in western BAT, but also on the associated crustal construction processes before the final arc-continent accretion.
... 锆石 CL 图像和 U-Pb 同位素年龄测定在西北大 学大陆动力学国家重点实验室进行, 详细的分析测 试步骤见文献 [26,27]. 斜长花岗岩(09HLG-07)的锆 石粒度较小, 粒径在 100 m 以下, 阴极发光图像(CL) 显示大部分锆石具有良好的晶形, 呈现岩浆结晶环 带或条带结构, 内部无残留核, 外部无变质边, 具有 岩浆锆石的特征(图 6). ...
... 全岩地球化学分析由中国地质科学院地球物理 地球化学勘查研究所实验室完成. 主量元素由 XRF 法测试, 分析精度优于 5%~10%; 微量元素由 ICP-MS 法测试, 分析精度优于 5%; 分析测试方法详见文 献 [21]. 本批样品 Sr-Nd-Pb 同位素分离测定由中国地 质 调 查 局 宜 昌 地 质 调 查 中 心 实 验 室 完 成 , 利 用 MAT-261 可调多接收型质谱仪测试同位素比值, 同 位素分析样品制备和分离流程在超净化实验室内完 成; 分析流程见文献 [22]. ...
... Data were acquired for 30 s with the laser off and 40 s with the laser on, giving ~100 mass scans. NIST SRM 610 glass (Pearce et al., 1997;Gao et al., 2002) and TEMORA zircon standards (Black et al., 2003) were used as external standards. We analyzed standards after every five samples. ...
Article
Zircon is a common accessory mineral in igneous rocks, including carbonatite-nordmarkite complexes. Zircons can record radiation damage and hydrothermal alteration through changes in oxygen isotope values, crystal structures, and geochemical and petrographic characteristics. The Mianning-Dechang rare earth element (REE) belt in China hosts 12 carbonatite-nordmarkite complexes and related Cenozoic REE deposits. We investigated zircons from these nordmarkites to understand the formation of the REE deposits. Three types of zircon from fresh and altered nordmarkite were identified. Type I zircons are unaltered, type II zircons experienced fenitization associated with hydrothermal alteration, and type III zircons were strongly affected by ore-forming fluids and REE mineralization. Type III zircons have higher Th, U, light REE, and REE contents (43,100, 52,000, 7,420, and 9,000 ppm, respectively) than type I zircons (1,450, 8,100, 265, and 1,130 ppm, respectively) and type II zircons (1,370, 19,520, 334, and 1,210 ppm, respectively). Petrographic observations, Raman spectra, and geochemical characteristics show that from type I to III zircons the crystals experienced increased radiation damage, hydrothermal alteration, and metasomatism by ore-forming fluids and show a transition to hydrothermal zircon. Type I, type II, and type III zircons have DaT (alpha dose) values of 0.6 to 29.5, 7.1 to 207, and 64 to 687 a-decay events/mg, with averages of 12.7, 87.36, and 144 a-decay events/mg, respectively. In general, the radiation damage trend shows that the Raman frequency is ~995 cm–1, even at high levels of radiation damage. However, the Raman frequency of type III zircon can reach 991 cm–1 with a line width of 28 cm–1, indicating type III zircons have a lower degree of crystallinity than type I and II zircons as a result of the effects of additional alteration by ore-forming fluids rich in Th and U. The involvement of ore-forming fluids and influx of meteoric water into the magmatic water is evident from the δ18O values of type I, II, and III zircons of 5.15 to 8.65‰, 1.50 to 6.24‰, and 1.92 to 5.86‰, respectively. U-Pb dating of type I zircons yields similar ages within a given deposit. Type II and III zircons could not be dated for the formation ages of REE deposits due to their high degree of alteration, abundant mineral inclusions, and variable common and radiogenic Pb contents. Given the chemical composition of the hydrothermal fluids and REE minerals, the geochemical characteristics of type III zircons suggest that highly evolved ore-forming fluids rich in Na, K, Ca, Cl, SO4, F, REEs, Th, U, Zr, Hf, and Pb facilitated zircon alteration. It is therefore concluded that the changes in zircon geochemistry and crystal characteristics could serve as a proxy for carbonatite-nordmarkite–related REE mineralization processes and as an indicator for REE exploration. A schematic model of the formation of type I, II, and III zircons and REE mineralization stages in the Mianning-Dechang REE deposits is presented.
... In situ trace elements of minerals were measured using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Detailed analytical procedures are described elsewhere (Gao et al., 2002). ...
Article
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This paper reports mineral and whole-rock geochemical data (major and trace elements, Sr–Nd isotopes, and in situ plagioclase Sr-isotope analysis) for Cenozoic volcanic rocks from Sabeto, NW Fiji, with the aim of constraining the origin of Cenozoic shoshonitic rocks found throughout Fiji. The most mafic shoshonitic lavas (absarokites) exhibit porphyritic textures and massive structure with phenocrysts of olivine (Fo = 76–78), clinopyroxene (Mg# = 73.9–80.0), and plagioclase (An = 71.9–92.1). Major element geochemical data include SiO2 = 47.31–48.46 wt%, MgO = 4.20–5.76 wt%, Mg# = 49–51, Al2O3 = 17.64–18.93 wt%, and (Na2O + K2O) = 5.12–7.01 wt%. The trace element geochemistry is typically arc like, with enrichment in the large ion lithophile elements (LILEs), the light rare earth elements (LREEs), and P, along with depletion in the heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs; e.g., Nb, Ta, Zr, Hf, and Ti). Whole-rock (⁸⁷Sr/⁸⁶Sr)i ratios and εNd(t) values vary from 0.7037 to 0.7039 and from +7.62 to +8.45, respectively. The former is near equal to the ⁸⁷Sr/⁸⁶Sr ratios of plagioclase phenocrysts (0.7034–07039). Based on these geochemical data and the results of previous studies, we propose that the Sabeto shoshonitic primary magma was derived from partial melting of the depleted lithospheric mantle, modified by subduction-related fluids. The thermobarometric calculation indicates that the P–T conditions of Fiji shoshonitic magma chamber are ~1100 °C and ~2.8 GPa (~90 km depth), with an average H2O fraction of ~6 wt%. In addition, the shoshonitic melts experienced fractional crystallization of clinopyroxene, olivine, and plagioclase during magma evolution. These volcanic rocks formed in an extensional setting following collision of the Vitiaz arc and the Ontong Java Plateau during the Pliocene.
... Instrument operating conditions were 80 mJ laser energy and a repetition rate of 8 Hz with a spot diameter of 33 μm and 40 s ablation time (Li et al., 2012; Liang et al., 2009; Tu et al., 2011). NIST SRM610 glass (Gao et al., 2002; Pearce et al., 1997) and TEMORA zircon standards (Black et al., 2003 ) were used as external standards. The offline selection and integration of background and analysis signals, and time-drift correction and quantitative calibration for trace elements and U–Pb dating were performed by ICP-MSDataCal (Liu et al., 2008Liu et al., , 2010). ...
Article
This paper reports zircon LA-ICPMS U-Pb ages and Hf-O isotopic ratios, and whole-rock major and trace element data of Early Cretaceous felsic intrusive rocks from Nagqu area, the northern Lhasa subterrane, southern Tibet. LA-ICPMS zircon U-Pb dating of biotite granites and biotite monzogranites in the area yields magmatic crystallization ages of ca. 112 Ma, which suggest that they were emplaced in the late Early Cretaceous. Both rocks show high-K calc-alkaline to shoshonitic composition and slightly - moderately peraluminous signature. They are enriched in the alkalis, Rb, Th, K, U and light rare earth elements, depleted in Nb, Ta, Ti and P, and characterized by high Al2O3 contents (12-16 wt.%), high Rb/Sr ratios (1.3-33) and low Mg# values (15-39). Their magmatic zircons have negative εHf(t) values (from -25.9 to 0.5) and high positive δ18O values (from 7.9‰ to 11.5‰). All the above characteristics indicate that Nagqu biotite monzogranites and biotite granites were likely derived from hybrid melts of sediments from the continent crust with minor mantle-derived input, then experienced varied degrees of fractional crystallization. The Nagqu intrusion is a component of the late Early Cretaceous magmatic flare-up event that occurred during ~ 120-100 Ma in the northern and partly central Lhasa subterranes. This magmatic flare-up is marked with a great compositional diversity (basalt, rhyolite, adakitic rocks, dioritic enclave, biotite monzogranite and granite) that might be caused by the slab breakoff of the southward subducting Bangong-Nujiang oceanic lithosphere, or more likely by slab window opening, which may have significantly contributed to juvenile crustal growth of the northern Lhasa subterrane.
... Diese Glä- ser wurden dem GLA von A. ROCHOLL dankenswerter Weise zur Verfügung gestellten. Als Referenz dienten die Ergebnisse analog hergestellter und mit unterschiedlichen Methoden untersuchter Proben (JOCHUM et al. 2000, GAO et al. 2002. ...
Article
Richard Klinger & Thomas Sperling We report a new approach for the quantifiation of Laser-ICP-MS analysis which was tested with various minerals of known composition. The method was applied to columbite samples from Bavarian pegmatites. Chemical data of most Bavarian columbite occurrences are lacking up to now. Furthermore the existence of columbite-(Fe), columbite-(Mn), tantalite-(Fe), tapiolite-(Fe) and ferberite could be confimed for the fist time in some of these pegmatites. Bezugsquelle: http://www.bestellen.bayern.de/application/applstarter?APPL=STMUG&DIR=stmug&ACTIONxSETVAL(artdtl_geo.htm,APGxNODENR:203252,AARTxNR:91110,USERxBODYURL:artdtl.htm,KATALOG:StMUG,AKATxNAME:StMUG,ALLE:x)=X
... program (Ludwig, 1999). Detailed analysis procedure and data processing follow the methods of previous workers (Gao et al., 2002;Yuan et al., 2004). ...
Article
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The Grove Mountains are the inland exposures of the Prydz Belt in East Antarctica. Although the 550–500 Ma orogenic event was recognized as the latest major magmatic-metamorphic activity in the Prydz Belt, its subduction-collision origin was not confirmed until the discovery of high-pressure (HP) mafic granulite erratic boulders in the glacial moraines from the Grove Mountains. Because no HP metamorphic bedrock is exposed in this area, an understanding the regional geology required a thorough study of the morainal debris mineralogy and detrital zircon U-Pb chronology. Detrital zircon U-Pb age histograms show 550–450 Ma, 900–800 Ma, and 1100–1000 Ma modes from three morainal deposits and one paleosol samples. The oldest ages were 2300 to 2420 Ma. Detailed electron probe microanalyses (EPMA) for the detrital mineral grains were compared with the minerals from the nearby exposed bedrock. The mineral chemistry indicates that the exposed bedrock in the Grove Mountains was not the sole source for morainal materials. This new U-Pb zircon geochronology and microprobe mineral data support the previous interpretation that the 550–500 Ma tectonic activity was the final collisional event that formed the Prydz Belt and amalgamated East Antarctica.
... During analysis, data quality was monitored by repeated analyses of USGS rock reference materials (BHVO-2, BCR-2, AGV-1, and G-2). See Gao et al. (2002) for analytical details. Table 1 gives the analytical data. ...
Article
Bulk-rock major and trace element, Sr-Nd-Hf isotope, zircon U-Pb age, and zircon Hf isotopic data of the Late Cretaceous Zhuogapu volcanic rocks in the northern Lhasa Terrane provide new insight into tectonic processes following collision of the terrane with the Qiangtang zone. SHRIMP zircon U-Pb dating reveals that the Zhuogapu volcanic rocks crystallized at ca. 91 Ma, postdating the development of a regional angular unconformity between the Upper Cretaceous and underlying strata in the Lhasa−Qiangtang collision zone. Compared to the Andean arc-type andesites and dacites, the Zhuogapu volcanic rocks are characterized by higher MgO of 2.78−5.86 wt.% and Mg# of 54−64 for andesites and MgO of 2.30−2.61 wt.% and Mg# of 55−58 for dacites. Eight andesite samples have whole-rock (87Sr/86Sr)i of 0.7054−0.7065, εNd(t) of − 3.2 - − 1.7, and εHf(t) of + 3.8 − + 6.4, similar to those of the three dacite samples with (87Sr/86Sr)i = 0.7056−0.7060, εNd(t) of − 2.7 - − 2.2, and εHf(t) of + 5.6 − + 7.0. Thirteen analyses from a dacite sample give positive zircon εHf(t) of + 5.6 to + 8.7. These signatures indicate that the Zhuogapu Mg-rich andesites were most likely derived from partial melting of a delaminated mafic lower crust (including lowermost crust straddling the northern and central Lhasa subterranes) that led to the generation of the Zhuogapu primary melts with adakitic signatures and small negative εNd(t). Such melts subsequently experienced interaction of melt-asthenospheric mantle peridotite followed by modification of highly fractionated magmas in shallow crustal magma chamber. Hornblende-controlled fractionation results in the change of geochemical composition from Mg-rich andesitic to Mg-rich dacitic magmas. Field observations, together with geochronological and geochemical data, indicate that the Zhuogapu Mg-rich volcanic rocks and coeval magmatism in the northern Lhasa subterrane may be the result of thickened lithospheric delamination following the final Lhasa–Qiangtang amalgamation.
... Helium was used as the carrier gas. External standard was NIST610, and internal standard was 42 Ca (for more analytical details, seeGao et al., 2002). CP, clinopyroxenite; CPM, clinopyroxene megacryst; GLH, garnet lherzolite; LH, lherzolite; SLH, spinel lherzolite; WH, wehrlite; Amph, amphibole; Cpx; clinopyroxene; Phl, phlogopite. ...
Article
In Central China, long-distance effects from collision between the North China and Yangtze cratons, uplift of the Tibetan Plateau and subduction of the Pacific Ocean are believed to converge in the Western Qinling. Mantle xenoliths from Baiguan and Haoti kamafugites in the Western Qinling were investigated to understand the lithospheric structure and mantle metasomatism beneath the orogenic belt. The Western Qinling lithosphere with depths of at least 120 km is geothermally hot and compositionally stratified, companied by a step-wise decrease in fertility with depth. The shallower portion of the lithospheric mantle is represented by type 2 xenoliths which lack alteration and deformation, and have fertile characteristics in compositions. The dominant rock type in the mantle section is the type 1 peridotites, which have had undergone relatively higher melt extraction and subsequent metasomatism. In-situ trace element data for minerals in the Baiguan and Haoti xenoliths are presented in this study. Baiguan clinopyroxenes have high LREE and show Ba, Th, U, Pb, Sr enrichment and negative Hf and Y anomalies, but the Haoti clinopyroxenes have large variations in trace elements and complicated distributions in LILE, and show negative Ti, Zr and Hf anomalies. Clinopyroxenes from both xenolith types have Ti/Eu and (La/Yb) N ratios in large ranges of 902–15,813 and 0–20, respectively. The petrological and geochemical characteristics suggest that the Western Qinling peridotites had been subjected to silicate and subsequent carbonatite metasomatism, and that carbonatite metasomatism was predominant in Baiguan but lesser in Haoti. Comparisons with the Western Qinling carbonatites and world-wide carbonatites indicate that carbonatite melts involved in the metasomatism originated from deep mantle and most likely related to carbonatite magma, with contributions from subducted oceanic crust. The type 2 peridotites, comprising clinopyroxene megacrysts and clinopyroxenite display similar trace element abundances and patterns, suggesting a close affinity in petrogenesis.
... The USGS and Chinese national standards BCR-1, BHVO-1, W-2 and GSR-3 were chosen for calibrating element concentrations of measured samples. The accuracy of USGS rock standards AGV-1 and BHVO-2, measured as unknowns , is within 10% of the recommended values (Gao et al., 2002; Govindaraju, 1994), but generally better than 5% for REE (Table 1). Sr and REE were separated on columns made of Sr and REE resins of the Eichrom Company using 0.1% HNO 3 as elutant. ...
Article
While the consensus has been reached as to the lithospheric thinning beneath the North China Craton, the timing of this event remains controversial. Whether it took place during the Early Cretaceous or it extended over a period from late Triassic to early Cenozoic is a matter of hot debate. With aims of contributing to this issue, we performed geochronological and geochemical analyses on basalts of the Laohutai Formation which were emplaced in the Fushun basin at 60-70 Ma. The Laohutai Formation consists of Ne- or Hy-normative alkali basalts in the lower part and Q-normative tholeiitic basalts in the upper part. The tholeiites are characterized by positive Eu and Sr anomalies and show higher epsilon(Nd)(t) (3.2-5.3) than the co-existing alkali basalts (1.8-2.4), opposite to the common observation made in other occurrences. Depletion of highly incompatible elements, positive Nb-Ta and negative Pb anomalies in the Laohutai basalts are indicative of oceanic crustal components (likely in form of pyroxenite/eclogite) in their magma source. Since Eu and Sr anomalies are not related to magmatic differentiation, the negative correlation between Sr-87/Sr-86(i) and Eu/Eu* suggests that the melting process and sampling of source heterogeneity are intrinsically related. We propose a differential melting of a two-component source in association with lithospheric thinning to account for the temporal variation of the Laohutai basalts. Specifically, earlier alkali basalts were formed by low degree of melting of a source at a greater depth, modified by melts derived from a hydrothermally altered, upper oceanic crust: whereas the later tholeiitic basalts were generated by high degree of melting of a gabbroic lower oceanic crust and minor peridotite at a shallower depth. When the lithospheric lid effect is applied, this petrogenetic model suggests the late Cretaceous-early Cenozoic as an important period of lithospheric thinning, therefore leaning support to the idea of the protracted destruction process beneath the North China Craton. (C) 2012 Elsevier B.V. All rights reserved.
... [37]. Additional detailed equipment characteristics and analytical procedures are found in [38][39][40]. ...
Article
Full-text available
Using in situ zircon dating by LA-ICP-MS and MC-ICP-MS, detrital zircon of 3981±9 Ma age was found in metamorphic rocks of the Ningduo Rock Group, Changdu Block of Northern Qiangtang. This is the oldest age record that has been found in the Qiangtang area. This finding also constitutes the third zircon locality in China with an age older than 3.9 Ga. Thus, the discovery provides new information for the study of Hadean crust. In addition, we found 3.51–3.13 Ga, ∼2440 Ma, ∼1532 Ma, ∼982 Ma and ∼618 Ma age peaks from 100 test spots. The younger ages of ∼982 Ma and ∼618 Ma correspond to the formation of the Rodinian super-continent and the Pan-African event, respectively. These findings suggest a close relationship between these zircons and the Gondwanan super-continent. The age of ∼618 Ma defines the lower limit on the deposit time of the protolith for the garnet-mica-quartz schist in the Ningduo Rock Group. Zircons with an age of ∼982 Ma generally display a negative ɛHf(t) and a two-stage Hf model with concentrated ages around 1933–2553 Ma. This pattern indicates that the source area of the Ningduo Rock Group underwent a significant separation of depleted mantle into the crust during the Paleoproterozoic Era. However, zircons with ages of 2854–3505 Ma also show a negative ɛHf(t) and a two-stage Hf model with a concentration of ages around 3784–4316 Ma. These results demonstrate that the source area of the Ningduo Rock Group contains a residual amount of ancient (Hadean) crustal materials. This paper provides new information on the relationship between the basement of the Qiangtang area and the Paleoproterozoic basements of the Gangdese and Himalayan regions, which constrains the northern boundary of Gondwana.
... The ICP-MS used for zircon U-Pb dating is Elan 6100DRC, the laser-ablation system is the GeoLas 200M DUV 193 nm ArF excimer laser ablation system that is produced by German Lamda Physik Company. This system has less elemental fractionation compared with the regular 266 nm or 213 nm Nd: YAG system [32] . The spot size of 30 μm was used in this study. ...
Article
Full-text available
Basalts of age between 120–100 Ma are rare in the North China Craton. The Dabeigou Group consists of olivine basalt in the lower part and andesite in the middle and upper parts. Zircons from the andesite are dated by LA-ICPMS and yielded a late Early Cretaceous age of 113.6 ± 0.87 Ma. Geochemical analyses of three basalt samples show depletion in high field-strength elements (Nb, Ta, Zr, Hf). Their 87Sr/86Sr ratio and ɛNd value are 0.7059 and-11.04 at 114 Ma. These values are consistent with a source from enriched lithospheric mantle. The source of the Dabeigou basalts is intermediate between those of
... nal standard was 42 Ca . International stand - ards of melted geological materials BCR - 2G , BHVO - 1G , AGV - 1G , and BIR - 1G were directly analysed by the ELA - ICP - MS before analysing the samples . The analytical uncertainties for the elements vary from < 5% to < 20% depending on the concentration levels ( for more analytical details , see Gao et al . , 2002 ) . ...
Article
A garnet–pyroxene rock containing abundant Ti-clinohumite (ca. 40 vol.%) occurs along with eclogites as small blocks in quartzo-feldsparthic gneiss in the southern end of the Chinese Su-Lu ultrahigh-pressure (UHP) metamorphic terrane. It consists of three aggregates: (1) Ti-clinohumite-dominated aggregate with interstitial garnet and pyroxene, (2) garnet+pyroxene aggregate with Ti-clinohumite inclusions, and (3) Ti-clinohumite-free aggregate dominated by garnet. Apatite, phlogopite, zircon, hematite, pentlandite, and an unknown Ni-Fe-volatile-Si (NFVS) mineral, which is replaced by Ni-greenalite, occur as accessories. Serpentine is the major secondary mineral. Garnet (Prp63.9–64.6Alm25.8–26.9Grs1.4–7.9Uva0.5–7.6Sps1.0) in all three aggregates is pyrope-rich with very low grossular component, with that in the aggregate (2) most enriched in Cr (Cr2O3=2.55 wt.%). Orthopyroxene is depleted in Al (Al2O3=0.16 wt.% in the cores) and Ca (CaO=0.06–0.09 wt.% in the cores), with XMg (Mg/(Mg+Fe)) values at ca. 0.900. Clinopyroxene is chromian diopside with Fe3+≥Fe2+. Matrix clinopyroxene has a lower XMg (0.862) than that (0.887) included in Ti-clinohumite. The rock contains modest amount of heavy rare earth elements (HREE) (10 to 12×C1 chondrite), with significant enrichment in Cr, Co, Ni, V, Sr, and light rare earth elements (LREE) (22 to 33×C1 chondrite). The clinopyroxene is very enriched in Cr (Cr2O3 is up to 2.09 wt.% in the cores) and Sr (ca. 350 ppm) and LREE (CeN/YbN=157.7). Ti-clinohumite is enriched in Ni (1981 ppm), Co (123 ppm), and Nb (85 ppm).
... The detection limits for analysis of mineral trace elements are shown in SupplementaryFig. 2. Further details of the experimental conditions and procedures can be found in Gao et al. (2002b). Trace element abundances of minerals are provided in Tables 3, 4 and 5. ...
Article
The North China Craton is the best example of an Archean craton that has lost its thick lithospheric keel. Although removal of the Archean keel is generally considered to have occurred in the Meosozoic–Cenozoic in the Eastern Block and Paleoproterozoic in the Central Orogenic Block, the exact timing and areal extent of the removal is debated, partly due to lack of knowledge about the nature of the Meosozoic lithospheric mantle. Here we report mineralogical and geochemical data on rare peridotite xenoliths from the Early Cretaceous high-Mg# diorites from Fushan in the Trans-North China Orogen (TNCO) of the North China Craton (NCC). These xenoliths provide insights into the nature of the lithospheric mantle underlying the central NCC during the Mesozoic. The peridotite xenoliths are dominated by spinel harzburgite and clinopyroxene (Cpx)-poor spinel lherzolite, with minor chromite-bearing dunite. The harzburgite and Cpx-poor lherzolite have average forsterite contents of 92.3 and are depleted in CaO (0.59–1.06wt.%) and Al2O3 (0.15–1.47wt.%). These features are similar to those of Archean cratonic lithospheric mantle, suggesting the presence of Archean cratonic mantle beneath the Central Orogenic Block of the NCC in the Early Cretaceous. Dunites make up ∼5% of the xenolith population and are characterized by relatively low Mg# (90.1) and the presence of disseminated chromite (Cr#=73–85). The olivines in the dunites have high Ca (320–770ppm) and Ti (18–29ppm) concentrations as well as low Ni abundances (2000–2690ppm) compared to those from harzburgite and Cpx-poor lherzolite (Ca=40–80ppm; Ti=0.23–8.1ppm; Ni=2970–3440ppm), suggesting that the dunites were produced through an interaction between the Archean lithosphere and siliceous melts. The presence of secondary phlogopite and amphibole in the harzburgite and Cpx-poor lherzolites as well as veined orthopyroxene in the foliated dunite is coupled with light rare earth element enrichments. Together with low Ca/Al (5–18) and LaN/YbN ratios (0.41–2.99) and high Ti/Eu ratios (526–1474) of clinopyroxenes, these metasomatic minerals indicate that the Archean lithospheric mantle had been overprinted by a volatile-bearing silicate melt. The Rb–Sr isochron age (111±23Ma) of the harzburgite and Cpx-poor lherzolite xenoliths shows that the metasomatic overprinting occurred in the Early Cretaceous, in agreement near the time of the emplacement of the host magma and coeval voluminous igneous activities in the NCC. This section of Mesozoic lithospheric mantle is markedly different from the contemporaneous lithospheric mantle in the eastern NCC, implying that the destruction of the NCC lithosphere was confined to the eastern NCC and that the Archean mantle was preserved in the central NCC.
... The relative analytical uncertainties for the elements vary from <5% to <20%, depending on the concentration levels. More analytical details have been given by Gao et al. (2002). The data are listed in Table 7. ...
Article
Layers of Ca-rich garnet–clinopyroxene rocks enclosed in a serpent-inite body at Hujialin, in the Su–Lu terrane of eastern China, preserve igneous textures, relict spinel in garnet, and exsolution lamellae of Ca-rich garnet, ilmenite/magnetite, Fe-rich spinel, and also amphibole in clinopyroxene. In terms of their major and trace element compositions, the studied samples form a trend from arc cumulates towards Fe–Ti gabbros. Reconstructed augite composi-tions plot on the trend for clinopyroxene in arc cumulates. These data suggest that the rocks crystallized from mantle-derived magmas differentiated to various extents beneath an arc. The Ca-rich garnet þ diopside assemblage is inferred to have formed by com-pressing Ca-rich augite, whereas the relatively Mg-rich cores of garnet porphyroblasts may have formed at the expense of spinel. The protolith cumulates were subducted from near the crust–mantle boundary (c. 1 GPa) deep into the upper mantle (4Á8 AE 0Á6 GPa and 750 AE 50 C). Negatively sloped P–T paths for the garnet– clinopyroxene rocks and the corollary of corner flow induced sub-duction of mantle wedge peridotite are not supported by the available data. Cooling with, or without, decompression of the cumulates after the igneous stage probably occurred prior to deep subduction.
... A detailed account of the analytical procedures has been given in the ref. [20]. ...
Article
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The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Himalaya orogenic episode. The geochronological study on the buried Shuangmaidi granite has confirmed the existence of the Cenozoic granitoids in the Baoshan Block. The present study indicates that: (1) It is medium- to coarse-grained two mica phyric granite, characterized by high SiO2 (73.55%–77.16%) and low CaO (0.34%–1.38%) contents, with a total alkalis (K2O+Na2O) of 5.22%–8.03%, K2O/Na2O ratios of 0.24–1.79, and total rare earth elements (ΣREE) of the granite between 85 and 125 ppb. All samples are enriched in light REE and exhibit medium negative Eu anomalies; and they show pronounced negative anomalies in Ba, Sr, Ti, and Nb but significant positive anomalies in K, Rb, U, Th, and Pb on mantle-normalized trace element patterns, indicating typically peraluminous to strongly peraluminous S-type granite. (2) The zircon SHRIMP U-Pb ages of the granite are 36.27±0.48 Ma for the samples from ZK7-1 and 35.78±0.49 Ma for those from ZK0-1, respectively. The similar zircon ages from these two drill cores may suggest that the granite samples come from the same buried pluton. (3) 206Pb/204Pb values of the granite vary from 20.115 to 25.359, 207Pb/204Pb from 15.776 to 16.160, and 208Pb/204Pb from 39.236 to 41.285, showing the characteristics of radioactive lead anomaly of the upper crust. The (87Sr/86Sr)i values calculated on the average age of the two-mica orthoclase granite (36 Ma) range from 0.72524 to 0.77503 and ɛNd(t) values vary from −10.9 to −11.7. These data, along with the depleted-mantle Nd modal ages of 1.73–1.80 Ga, imply that the granites might have formed from partial melting of the Precambrian crystal basements. (4) On the Hf-Rb-Ta diagram, almost all the samples fall within the field of post-collision tectonic setting. The CaO/Na2O and Al2O3/TiO2 ratios suggest that the granitic magma may have formed from partial melting of clay-rich crustal materials with a possible melting temperature of about 900°C and a possible crystallization temperature of 775–795°C. (5) During the post-collision of the Himalaya orogen, with the southeastward extrusion of the Indochina continent resulting from the continuous northward indentation of the India continent into the Asia, the Gaoligong Fault, as the western boundary of the Indochina continent, moved in the dextral strike-slip on a large scale to trigger partial melting of the thickened crust, and the peraluminous granitic magma from which the Shuangmaidi two-mica orthoclase granite derived was formed. KeywordsUpper Eocene peraluminous granite–elements and Sr-Nd-Pb isotopic geochemistry–Himalayan post-collision orogenic setting–Baoshan Block–southwestern China
... Analyses of US Geological Survey basalt glass standards BCR-2G and BHVO-2G, which have rare earth element (REE), Sr, and Y concentrations similar to the clinopyroxenes analyzed in the present study, demonstrate analytical precision and accuracy better than 7%. Further details of the analytical conditions and procedures can be found in Gao et al. (2002b). ...
Article
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This article reports the petrography and mineral chemistry of dunite xenoliths and olivine xenocrysts entrained by the Early Cretaceous Xi’anli (西安里) hornblende (Hb)-gabbros from the southern Taihang (太行) Mountains, with the aim of constraining the nature of the Mesozoic lithospheric mantle in Central China. Rounded dunite xenoliths are 1–3 cm3 in size and display porphyroclastic, tabular, and protogranular textures. Chromite with Cr#=60–89 is common in the xenoliths. Olivine xenocrysts of 4–6 mm in size are also found in the Hb-gabbros. Orthopyroxene reaction rims are commonly observed around olivine xenocrysts or between dunite xenoliths and host rocks. The porphyroclastic olivines within dunite xenoliths and olivine xenocrysts have kink bands and Mg#=83–94. The Mg# of olivine cores and rims are 89–94 (average, 90) and 83–86 (average, 84.4), respectively. The CaO contents of all olivines from the xenoliths and xenocrysts are less than 0.1 wt.%, suggesting a lithospheric mantle origin. The Ca content (214 ppm–818 ppm) and Ti content (15 ppm–137 ppm) in the xenoliths and xenocrysts are similar to those of olivines from the dunite xenoliths, but are much higher than those of olivines from harzburgite and lherzolite xenoliths in the Fushan (符山) intrusion. This finding implies that the xenoliths and xenocrysts may have originated from harzburgites or lherzolites that were intensively modified by silica-rich melts. This result, combined with high Mg# (92–94) of olivine cores from the dunite xenoliths and xenocrysts, indicates that these olivine xenocrysts and dunite xenoliths could represent the residue of ancient (Archean or Paleoproterozoic) lithospheric mantle and might have experienced the same intensive modification by silica-rich melts as the host magma, resulting in enrichment in MgO and SiO2. Key WordsNorth China craton-Xi’anli-Hb-gabbro-dunite-xenocryst-lithospheric mantle
... In situ trace elements were measured using laser-ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Detailed analytical procedures are described elsewhere (Gao et al. 2002). Helium was used as the carrier gas to enhance transport efficiency of ablated material. ...
Article
Spongy textures are observed in mantle peridotite xenoliths hosted in Cenozoic kamafugites from the Western Qinling, central China. These textures are mainly developed in clinopyroxenes and spinels, and occur as spongy rims consisting of low-Na clinopyroxene, ilmenite, and bubbles, enclosing nonspongy cores. The ilmenites and bubbles exhibit shapes and sizes that vary with the width of the spongy rims. The spongy-textured minerals preserve primary shapes and well-defined grain boundaries and do not show apparent interaction with contact minerals or observed melts except the subsequent melts forming melt pockets. The xenocrysts display reactive zoning textures with host magmas rather than spongy textures. Compositionally, the spongy rims are enriched in Ca, Ti, and most trace elements, have high Cr#, and are depleted in Na, Al, Fe, AlVI, and AlIV/AlVI compared with the cores. These observations suggest that melts/host magmas did not play any significant role in the formation of the spongy textures. We therefore propose that spongy-textured clinopyroxenes and spinels in Western Qinling peridotite xenoliths developed from a decompression-induced partial melting event prior to formation of melt pockets and xenolith entrainment in host magmas. KeywordsDecompression–Mantle peridotite–Partial melting–Spongy texture–Western Qinling
... These results indicate the capabilities of our method for quantitative trace element analysis of NIST612 and NIST614 glasses. Due to relative matrix-independence in element determination by 193 nm ArF laser [17,18] , the good agreements between measured and recommended values for 40 trace elements in basalt glasses was obtained [19] . For the same reason, the LA-ICP-MS method using NIST610 as reference material for determining trace elements in miner-als, such as zircon [8][9][10] , apatite, pyroxene and garnet, was used extensively. ...
Article
Full-text available
Simultaneous in-situ determination of U-Pb ages and 20 trace elements of three international zircon standards (91500, GJ1 and TEMORA 1) and one laboratory zircon standard (SK10-2) separated from Cenozoic fine-grained gabbro was carried out on quadrupole ICP-MS equipped with 193 nm excimer laser in 20 μm spot size. The weighted mean 206Pb/238U ages of 91500, GJ1 and TEMORA 1 are 1064.4±4.8 Ma (2σ), 603.2±2.4 Ma (2σ) and 418.2±2.4 Ma (2σ), respectively. The relative standard deviations (RSDs) of 206Pb/238U ages (2σ) are less than 2.2% for single measurements and 0.6% for weighted means. The obtained weighted mean 206Pb/238U ages of three standard zircons agree with the recommended values within 2σ error. The weighted mean 206Pb/238U age of SK10-2 is 31.42±0.25 Ma (2σ) and the RSDs of 206Pb/238U ages (2σ) are between 2.4% and 5.7% for single measurements and less than 0.8% for weighted mean. The obtained weighted mean 206Pb/238U age is in good agreement with the age obtained by Yuan (2004). Trace element concentrations of NIST612 and NIST614 obtained under the same LA-ICP-MS operating conditions agree with the recommended values within analytical error. The results indicate that it is possible to measure U-Pb age and trace elements simultaneously by LA-ICP-MS in a small spot size of 20 μm.
... Trace elements were determined using an Agilent 7500 a ICP-MS with analytical uncertainties generally better than 5%-10%. The analytical details are given in ref. [38]. Sample preparation for Sr and Nd analysis was also done at the SKLCD, while actual Sr-Nd isotopic analysis was done using a Finnigan MAT-261 mass spectrometer at China University of Geosciences (Wuhan). ...
Article
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The Cretaceous granitoids in the middle and northern Gangdese, Tibet are generally interpreted as the products of anatexis of thickened deep crust genetically associated with the Lhasa-Qiangtang collision. This paper reports bulk-rock major element, trace element and Sr-Nd isotopic data, zircon U-Pb age data, and zircon Hf isotopic data on the Zayu pluton in eastern Gangdese, Tibet. These data shed new light on the petrogenesis of the pluton. Our SHRIMP zircon U-Pb age dates, along with LA-ICPMS zircon U-Pb age dates recently reported in the literature, indicate that the Zayu pluton was emplaced at about 130 Ma, coeval with Early Cretaceous magmatic rocks in other areas of eastern Gangdese (e.g., Rawu, Baxoi areas) and the Middle Gangdese. The Zayu pluton samples lack amphibole and muscovite, and are compositionally characterized by high SiO2 (69.9%–76.8%), K2O (4.4%–5.7%), and low P2O5 (0.05%–0.12%). These samples also have A/CNK values of 1.00–1.05, and are enriched in Rb, Th, U, and Pb, and depleted in Ba, Nb, Ta, Sr, P, Ti, and Eu. These geochemical features suggest that the Zayu pluton samples are metaluminous to slightly peraluminous and are of highly fractionated I-type granite. The Zayu pluton samples have high ɛ Nd(t) values (−10.9–−7.6) and low initial 87Sr/86Sr ratios (0.7120–0.7179) relative to melts derived from mature continental crust in the Gangdese (e.g., Ningzhong Early Jurassic strongly peraluminous granite). The Zayu pluton samples are heterogeneous in zircon ɛ Hf(t) values (−12.8–−2.9), yielding ancient zircon Hf crustal model ages of 1.4–2.0 Ga. The data obtained in this study together with the data in the recent literature suggest that the Early Cretaceous granitoids in eastern Gangdese represent the eastward extension of the Early Cretaceous magmatism in the middle Gangdese, and that the Lhasa micro-continent block with ancient basement may extend for ∼2000 km from east to west. Zircon Hf isotopic data and bulk-rock zircon saturation temperature (789–821 °C) indicate that mantle-derived materials likely played a role in the generation of the Zayu pluton. We propose that the Zayu pluton was most likely generated in a setting associated with southward subduction of the Bangong-Nujiang ocean floor, where mantle wedge-derived magmas may have provided the heat and material for the anatexis of ancient crust of the Lhasa micro-continent, resulted in hybrid melts (i.e., mantle-derived basaltic magmas + crust-derived felsic magmas). Such hybrid melts with subsequent fractional crystallization are responsible for the highly evolved Zayu pluton (crust thickening is not a prerequisite).
Article
Neoproterozoic magmatism associated with the assembly and configuration of the Rodinia supercontinent is widely distributed in the India-Himalayan terrane. However, its petrogenesis and tectonic settings remain controversial. This study provides new geochronological and geochemical data on the Neoproterozoic bimodal magmatism from the eastern Himalayan orogen. In situ zircon UPb dating revealed that the protoliths of amphibolites were emplaced at ca. 826 Ma and the granitic gneisses have crystallization ages of 825–820 Ma. The granitic gneisses exhibit geochemical features of A-type granites, with high initial (⁸⁷Sr/⁸⁶Sr)i ratio (0.7182–0.7394), low whole-rock εNd(t) (−8.4 to −6.6), and variable zircon εHf(t) (−7.4 to +1.0) values. They were probably generated by partial melting of the ancient lower crust with minor input of mantle components. The amphibolite samples are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), suggesting an arc affinity. They have relatively high initial (⁸⁷Sr/⁸⁶Sr)i ratios (0.7113–0.7136), low whole-rock εNd(t) (−1.1 to 1.4) and a wide range of zircon εHf(t) (−4.1 to 8.3) values, indicating that the protoliths of amphibolites were likely generated by partial melting of an enriched subduction-modified continental lithospheric mantle. Their geochemical signatures are similar to typical back-arc basin basalts. The presence of coeval A-type granites and arc-related mafic rocks is probably due to the existence of a back-arc system. We argue that the Neoproterozoic bimodal magmatism is a product of back-arc extension initiated at an early stage, resulting from the rollback of the Mozambique Oceanic slab. Combined with previous studies on Neoproterozoic magmas from India and the Himalayas, we suggest that an extensive Neoproterozoic back-arc system may have existed along the northwestern margin of the Rodinia supercontinent. This theory supports a scenario of an Andean-type continental margin for the India-Himalayan terrane during the middle Neoproterozoic.
Article
The Dabaoshan Cu–Pb–Zn–Mo–W polymetallic deposit in northern Guangdong Province, South China, lies in the southern part of the Qin–Hang porphyry–skarn CuMo ore belt and hosts both porphyry Mo and stratabound skarn Cu ores. The genesis of the Cu ore has been ascribed to typical skarn ore formed by the metasomatism of Devonian carbonate rock layers, or to a sediment-rock-hosted massive sulfide deposit formed by marine exhalation. In this paper, we report the ages of porphyry Mo and stratiform Cu ores and dacitic porphyry determined with molybdenite ReOs, sericite Ar/Ar, and zircon UPb methods, respectively. Nine samples from the granodiorite porphyry Mo ores yielded ReOs model ages ranging from 165.7 ± 2.3 to 163.4 ± 2.4 Ma, with a weighted mean age of 164.8 ± 0.8 Ma (MSWD = 0.52). Sericite from two samples of stratiform Cu ores yielded ages of 166.6 ± 1.6 Ma (DB011) and 171.7 ± 2.0 Ma (DB020), with corresponding reverse isochron ages of 167.0 ± 2.0 Ma and 161.7 ± 1.7 Ma, respectively. The age data determined from ReOs analyses of molybdenite and ⁴⁰Ar/³⁹Ar dating of sericite are in good agreement with each other, indicating that the porphyry Mo and stratiform Cu potentially originated from the same ore system and may be genetically associated with Jurassic granitic granodiorite porphyry. In this study, magmatic zircon weighted mean ages of 434.3 ± 1.0 Ma (DB009), 431.5 ± 0.12 Ma (DB022), and 427.0 ± 0.87 Ma (DB031) from three samples for the Dabaoshan dacitic porphyry indicate that the mineralization in the Dabaoshan deposit is mainly related to the invasion of Jurassic granitic magma, not to Silurian subvolcanic rocks. Based on the integrated geological, geophysical, and geochemical data, we proposed the Dabaoshan porphyry–skarn Cu–Pb–Zn–Mo–Wpolymetallic deposit to be part of the Qin–Hang porphyry–skarn CuMo ore belt that formed during the low-angle Jurassic subduction of the Paleo-pacific plate under Eurasian continent.
Article
The Hutouya Pb–Zn mining district in the Qiman Tagh region in NW China is a zoned skarn district with inner Fe–Sn–Cu–Co ores and outer Pb–Zn skarn mineralization. Temporal coincidence of ⁴⁰Ar/³⁹Ar plateau age of ore-stage phlogopite (226.9 ± 1.5 Ma) with weighted mean LA–ICP–MS U–Pb ages of zircons (230.3 ± 3.7 and 221.6 ± 1.3 Ma) and ⁴⁰Ar/³⁹Ar plateau ages of biotite (229.6 ± 2.3 and 224.7 ± 2.6 Ma) in the spatially-associated monzogranite strongly suggest a genetic relationship between skarn formation in the Hutouya metallogenic district and intrusion of the monzogranite suite. Major and REE analyses indicate the Hutouya monzogranites are A-type granites that belong to the high-K calc–alkaline series. Hafnium isotope data are consistent with a crust–mantle mixing source. Geochemical characteristics of the Middle–Late Triassic Indosinian (235–204 Ma) granitoids associated with mineralization in the Qiman Tagh region are consistent with an origin as post-collisional, mantle-derived magmas that underplated the lower crust in the East Kunlun orogen in an extensional setting, causing lower crustal melting and subsequent mixing and assimilation that produced magmas fertile for mineralization.
Article
Miocene postcollisional potassic and adakitic rocks are widely distributed in the southern Lhasa terrane and western central Lhasa terrane. However, coeval potassic and adakitic rocks in eastern central Lhasa terrane were rarely recognized, and their origins and formation mechanism remain controversial. In this paper, we provide new geochronological and geochemical data for the Miocene postcollisional potassic and adakitic intrusions exposed in the Qingdu area, eastern central Lhasa terrane, southern Tibet. The Qingdu Miocene intrusions consist of quartz monzonite porphyry and biotite granite with coeval zircon U–Pb ages of 14.1 Ma and 14.0 Ma, respectively. They have high SiO2 (67.98–75.32 wt.%), Al2O3 (14.13–14.78 wt.%), and K2O (4.06–6.18 wt.%) and low MgO (0.25–1.46 wt.%) contents. They are both enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), with high (La/Yb)N (25.37–42.32) ratios. The biotite granite samples have low Y (7.10–9.96 ppm) and Yb (0.61–0.85 ppm) contents, and high Sr (229–384 ppm) contents and high Sr/Y (30–41) ratios, which show adakitic geochemical characteristics, whereas the quartz monzonite porphyry samples show potassic geochemical characteristics. They display initial (87Sr/86Sr)i ratios of 0.7083–0.7103, εHf(t) values of −6.7 to −0.1, εNd(t) values of −8.96 to −7.44, (208Pb/204Pb)i ratios of 39.028–39.110, (207Pb/204Pb)i ratios of 15.662–15.684, and (206Pb/204Pb)i ratios of 18.541–18.577. These signatures indicate that both the potassic and adakitic intrusions are more likely to originate from partial melting of a thickened lower crust, which were mainly the products of the binary mixing between the juvenile and ancient crust components. Based on the spatial distributions and isotopic features of the postcollisional potassic and adakitic rocks in the Lhasa terrane, we suggest that the differences of the lower crustal composition played a crucial role in causing the geochemical variations of the Miocene postcollisional adakitic and potassic rocks in Lhasa terrane.
Article
Northeastern China contains widely distributed Jurassic terrestrial strata that have yielded many spectacular mammal and pterosaur fossils, in addition to feathered dinosaur fossils and more recent discoveries from Jianchang, particularly from western Liaoning. However, the fossil‐bearing stratigraphic succession, regional correlation, and age estimates of the fossils found in Jianchang County and nearby areas have been contentious. Here, we report on the vertebrate fossil‐bearing Jurassic stratigraphy from Linglongta, Jianchang County, western Liaoning, including a SHRIMP U‐Pb zircon date unambiguously associated with the fossil horizons. The primary goal was to determine the vertebrate fossil‐bearing succession. A further aim was to provide age estimations for the fossil‐bearing horizon as well as the earliest appearance of feathered dinosaurs, the eutherian–placental clade, and transitional pterosaurs. Field investigations showed that the vertebrate fossil‐bearing stratigraphic succession in Jianchang County mainly consists of basal andesites overlain by rhythmic tuffs and tuffaceous lacustrine sediments, with the upper intermediate or acidic lavas interbedded with laminated more or less tuffaceous lacustrine deposits. This sequence correlates well with the Middle Jurassic Lanqi/Tiaojishan Formation in northeastern China. Detailed and accurate field observations showed that the well‐preserved vertebrate fossils were buried in either the middle or the upper fine‐grained laminated lacustrine deposits. Previous and current SHRIMP U‐Pb zircon dates provide an age estimation of 161–159 Myr for the fossil‐bearing horizon and vertebrates. This indicates that the earliest appearance of feathered dinosaurs here was more than 159 Myr ago and unquestionably older than Archaeopteryx from Germany, making these the earliest known feathered dinosaurs in the world. Furthermore, the eutherian–placental clade and the known transitional pterosaurs first emerged no later than 161 Myr. The vertebrate assemblage unearthed recently from Linglongta and neighboring areas in Jianchang County belongs to the Daohugou Biota. In addition to feathered dinosaurs, this biota was characterized by mammals, primitive pterosaurs, insects, and plants and was present in Inner Mongolia, western Liaoning, and northern Hebei in northeastern China during the Middle–Late Jurassic.
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The Lakange porphyry Cu–Mo deposit within the Gangdese metallogenic belt of Tibet is located in the southern–central part of the eastern Lhasa block, in the Tibetan Tethyan tectonic domain. This deposit is one of the largest identified by a joint Qinghai–Tibetan Plateau geological survey project undertaken in recent years. Here, we present the results of the systematic logging of drillholes and provide new petrological, zircon U–Pb age, and molybdenite Re–Os age data for the deposit. The ore-bearing porphyritic granodiorite contains elevated concentrations of silica and alkali elements but low concentrations of MgO and CaO. It is metaluminous to weakly peraluminous and has A/CNK values of 0.90–1.01. The samples contain low total REE concentrations and show light REE/heavy REE (LREE/HREE) ratios of 17.51–19.77 and (La/Yb)N values of 29.65–41.05. The intrusion is enriched in the large-ion lithophile elements (LILE) and depleted in the HREE and high field-strength elements (HFSE). The ore-bearing porphyritic granodiorite yielded a Miocene zircon U–Pb crystallization age of 13.58 ± 0.42 Ma, whereas the mineralization within the Lakange deposit yielded Miocene molybdenite Re–Os ages of 13.20 ± 0.20 and 13.64 ± 0.21, with a weighted mean of 13.38 ± 0.15 Ma and an isochron age of 13.12 ± 0.44 Ma. This indicates that the crystallization and mineralization of the Lakange porphyry were contemporaneous. The ore-bearing porphyritic granodiorite yielded zircon εHf(t) values between −3.99 and 4.49 (mean, −0.14) and two-stage model ages between 1349 and 808 Myr (mean, 1103 Myr). The molybdenite within the deposit contains 343.6–835.7 ppm Re (mean, 557.8 ppm). These data indicate that the mineralized porphyritic granodiorite within the Lakange deposit is adakitic and formed from parental magmas derived mainly from juvenile crustal material that partly mixed with older continental crust during the evolution of the magmas. The Lakange porphyry Cu–Mo deposit and numerous associated porphyry–skarn deposits in the eastern Gangdese porphyry copper belt (17–13 Ma) formed in an extensional tectonic setting during the India–Asia continental collision.
Article
The Ga'erqiong-Galale skarn–porphyry copper–gold ore-concentrated area is located in the western part of the Bangong-Nujiang suture zone north of the Lhasa Terrane. This paper conducted a systematic study on the magmatism and metallogenic effect in the ore-concentrated area using techniques of isotopic geochronology, isotopic geochemistry and lithogeochemistry. According to the results, the crystallization age of quartz diorite (ore-forming mother rock) in the Ga'erqiong deposit is 87.1 ± 0.4 Ma, which is later than the age of granodiorite (ore-forming mother rock) in the Galale deposit (88.1 ± 1.0 Ma). The crystallization age of granite porphyry (GE granite porphyry) in the Ga'erqiong deposit is 83.2 ± 0.7 Ma, which is later than the age of granite porphyry (GL granite porphyry) in the Galale deposit (84.7 ± 0.8 Ma).The quartz diorite, granodiorite, GE granite porphyry and GL granite porphyry both main shows positive εHf(t) values, suggesting that the magmatic source of the main intrusions in the ore-concentrated area has the characteristics of mantle source region. The Re–Os isochron age of molybdenite in the Ga'erqiong district is 86.9 ± 0.5 Ma, which is later than the mineralization age of the Galale district (88.6 ± 0.6 Ma). The main intrusive rocks in the ore-concentrated area have similar lithogeochemical characteristics, for they both show the relative enrichment in large-ion lithophile elements(LILE: Rb, Ba, K, etc.), more mobile highly incompatible lithophile elements(HILE: U, Th) and relatively depleted in high field strength elements (HFSE: Nb, Ta, Zr, Hf, etc.), and show the characteristics of magmatic arc. The studies on the metal sulfides' S and Pb isotopes and Re content of molybdenite indicate that the metallogenic materials of the deposits in the ore-concentrated area mainly come from the mantle source with minor crustal source contamination. Based on the regional tectonic evolution process, this paper points out that the Ga'erqiong-Galale copper–gold ore-concentrated area is the typical product of the Late Cretaceous magmatism and metallogenic event in the collision stage of the Bangong-Nujiang suture zone.
Article
The study area is located at the southern margin of the Middle Qilian, south of the Qinghai Lake—GuLei deep fault belt, which is a favorable area for copper-nickel deposits in Qilian metallogenic belt. Yishichun Copper-nickel ore occurs within the homologous and contemporaneous basic-ultrabasic intrusions, and copper-nickel mineralization is spatially and temporally related to the intrusive rocks. The cathodoluminescence (CL) images and the Th/U ratios of zircons from the basic-ultramafic rocks suggest that zircon crystals are of magmatic origin; The LA-ICP-MS U-Pb dating of these zircons yields a weighted mean age of 455.1±1.7 Ma. Therefore, the ore-bearing rock emplacement and copper-nickel mineralization occurred during the late Ordovician, and the metallogenic dynamic process was probably related to an ancient continental margin rifting.
Article
This paper reports petrological and geochemical features and zircon U-Pb age of plagiogranite from the Hongliugou-Lapeiquan ophiolitic mélange belt in the northern Altyn Tagh. The zircon U-Pb dating results yield a mean 238U/206Pb age of 512.1 ± 1.5 Ma, representing an emplacement time of the plagiogranites in the Middle Cambrian. The plagiogranites are interpreted to have derived from anatexis of hydrated amphibolites by ductile shearing during transports of the oceanic crust. Thus it is believed that the formation age of such type of plagiogranite was coeval to or slightly younger than the spreading of the Hongliugou-Lapeiquan limited oceanic basin. The new results from the plagiogranites suggest that an oceanic basin existed in the northern Altyn area during the Middle Cambrian.
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Eclogite and peridotite xenoliths occur in early Cretaceous high-Mg adakites of the eastern North China craton (NCC). The primary mineral assemblage (garnet + omphacite + quartz + rutile pargasite), and garnet and quartz-rod exsolutions in clinopyroxene in the eclogite xenoliths constrains a minimum pressure of >1.5 GPa, while the estimated peak metamorphic temperatures range from 800 to 1060 °C (Xu et al., 2004, 2006). SHRIMP zircon U-Pb age information and the geochemistry of the eclogite xenoliths indicate that eclogite- facies metamorphism occurred in the Triassic (220-240Ma) and that their protoliths were most likely to have been basalts from the NCC basement (1800 and 2500Ma). This implies that the Triassic thickening, foundering and partial melting of the Archean NCC mafic lower crust took place, an interpretation further supported by the complementary major and trace element compositions between these xenoliths and their host high-Mg adakitic intrusions (Xu et al., 2006). The high-Mg character of host intrusions may have resulted from the interaction between melts derived from delaminated lower crust and mantle peridotite. The peridotite xenoliths hosted in adakitic rocks mainly consist of dunite (95%), harzburgite (3%), and lherzolite (2%). In addition to the veins of orthopyroxene and orthopyroxene+phlogopite in dunites, the increase in TiO2, Al2O3, and FeOt contents and decrease in Cr2O3 content from core to rim for chromites, as well as the increase in TiO2, Cr2O3 contents and decrease of NiO content from core to rim for olivines, from dunite xenoliths imply metasomatism of the Archean lithospheric mantle (Gao et al., 2006) by hydrous silicate melts. Further evidence for this is provided by the trace element compositions of these rocks. The dunite and harzbugite xenoliths are relatively enriched in light rare earth elements and large ion lithophile elements, yet have low abundances of heavy rare earth elements and high field strength elements (HFSE), and lack any Eu anomaly. The initial 87Sr/86Sr ratios and epsilon Nd(t) values for the xenoliths range from 0.7058 to 0.7212 and +0.18 to _10.65, respectively. Taken together, these results, combined with the strong depletion in HFSE in the host rocks, suggests that the hydrous silicate melt had been derived from the partial melting of early Mesozoic delaminated lower continental crust. The observed large Re-Os isotopic variations of peridotite xenoliths can be explained by the reaction of pristine Archaean mantle (TRD=2.6-2.8 Ga) with eclogite-derived melt (Gao et al., 2006).
Article
The North China Craton (NCC) is proposed to have formed by collision between the Western and Eastern blocks at ∼1.85Ga. However, the detailed history of the individual blocks remains unsolved. In the Eastern block, the Paleoproterozoic volcano-sedimentary rocks are mainly exposed along its eastern margin, and are referred to as the Liaohe Group in the Liaodong Peninsula of Liaoning Province and as the Guanghua, Ji’an and Laoling Groups in the Tonghua area of southern Jilin Province. The Guanghua and Ji’an Groups are characterized by the occurrence of volcanic rocks, whereas the Laoling Group is composed of clastic sediments and carbonates. Zircon U–Pb isotopic dating by LA-ICP-MS and SHRIMP methods indicates that the Guanghua and Ji’an Groups were formed between 2.1 and 2.0Ga, but that the rocks of the Laoling Group may have formed in two episodes at 2.5–2.2 and 2.0–1.9Ga, respectively. The present data indicate that the Ji’an, Laoling and Liaohe Groups are chaotic, without a common stratigraphy, with intense deformation making it difficult to identify original layering and contact relationships. Combined with age data from rocks intrusive into the sequence, the Paleoproterozoic tectonic evolution of the Liaoning–Jilin area can be related to collision and extension between the Liaonan block to the south and the Longgang block to the north. Extension in the Longgang block occurred at 2.12–1.98Ga and was represented by eruption of the Guanghua mafic volcanic rocks. However, extension in the Liaonan block is expressed by 2.16–2.09Ga A-type granites and ∼2.12–1.98Ga volcano-sedimentary rocks of the Ji’an Group. These two blocks collided at ∼1.93–1.90Ga, resulting in a clockwise metamorphic P–T path recorded in the N. Liaohe–Laoling Groups, followed by ∼1.85Ga post-collisional evolution expressed by anticlockwise metamorphic P–T paths and immense granitic intrusions in the S. Liaohe–Ji’an Groups. Therefore, it is suggested that the collision between the Longgang and Liaonan in the Eastern block of the NCC occurred a little earlier than ∼1.85Ga, when the NCC amalgamated by collision of the Western and Eastern blocks.
Article
Zircon U-Pb dating by both SHRIMP and LA-ICP-MS and geochemical study of the Tiaojishan Formation and the Donglintai Formation from Xishan, Beijing, reveal that ages of upper lavas of Tiaojishan Formation and Middle of Donglintai Formation are 137.14.5 Ma(2σ) and 130-134 Ma, respectively. The fomer is slightly older than the latter and the age difference between these two formations is less than 5 Ma. These lines of evidence prove that the two volcanoes erupted within a short time. The age of the Tiaojishan Formation from Xishan, Beijing is distinctively different from that of the Chende Basin. This indicated that the ages of Tiaojishan lavas varied in different regions. The Tiaojishan Formation consists of typical adakite (SiO2=56%, Na2O = 3.99-6.17, Na2O/K2O = 2.2-3.1, Sr = 680-107410-6, Y = 13.2-16.310-6, Yb = 1.13-1.5210-6, Sr/Y = 43-66), high-Mg adakite and high-Mg andesite (Mg# = 54-55). Features of continental crust of adakite from the Tiaojishan Formation and its syngeneric middle silicic vocanic rocks, such as typical Nd-Ta negative abnormality and Pb possive abnormality, indicate that these lavas are originated from partial melts of continental crust. These results suggest that the adakite from the Tiaojishan Formation of Xishan, Beijing derived from thickened eclogitic lower crust and lithosphere beneath the North China craton at mesozoic that was foundered into the aesthenosphere, and subsequenctly partially melted and interacted with mantle olivine during melts upward migration. The age of lavas from the Tiaojishan Formation restrained the foundation which should last at least until 137 Ma. Lavas of the Donglintai Formation are rhyolith and andesite with normal Mg# and thus they did not interact with the mantle. These lavas represent remobilized melts of lower crust material caused by mantle aesthenosphere upwelling migration induced by foundation.
Article
Abundant dunite and harzbugite xenoliths are preserved in Early Cretaceous high-Mg# [63–67, where Mg# = molar 100 × Mg/(Mg + Fetot)] diorite intrusions from western Shandong in the North China Craton (NCC). Dunite and some harzburgite xenoliths typically preserve areas of orthopyroxenite (sometimes accompanied by phlogopite) either as veins or as zones surrounding chromite grains. Harzburgite is chiefly composed of olivine, orthopyroxene, minor clinopyroxene and chromian-spinel. High Mg#'s (averaging 91.4) and depletions in Al2O3 and CaO (averaging 0.52 wt.% and 0.29 wt.%, respectively) in harzburgite and dunite xenoliths suggest that they are residues formed by large degrees of polybaric melting. However, olivines and orthopyroxenes from dunite xenoliths spatially associated with orthopyroxenite display lower Mg#'s (i.e., 82–87 and 83–89, respectively), suggesting that an adakitic melt–peridotite reaction has taken place. This is consistent with the production of veined orthopyroxene or orthopyroxene + phlogopite in dunite and some harzburgite xenoliths in response to the introduction of adakitic melt into the previously depleted lithospheric mantle (i.e., harzburgite and dunite xenoliths). The presence of orthopyroxene in veins or as a zones surrounding chromite in peridotite xenoliths is thought to be representative of adakitic melt metasomatism. The dunite and harzbugite xenoliths are relatively rich in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), poor in heavy rare earth elements (HREEs) and high field strength elements (HFSEs), and lack Eu anomalies on chondrite normalized trace element diagrams. The initial 87Sr/86Sr ratios and εNd(t) values for the xenoliths range from 0.7058 to 0.7212 and + 0.18 to − 19.59, respectively. Taken together, these features, combined with the strong depletion in HFSE and the existence of Archean inherited zircons in the host rocks, suggest that the adakitic melt was derived from the partial melting of early Mesozoic delaminated lower continental crust. The interaction of the adakitic melt with peridotite is responsible for the high-Mg# character of the early Cretaceous diorites in western Shandong.
Article
Using the in situ zircon U-Pb dating method of LA-ICPMS, we analyzed the 31 Ma old SHRIMP U-Pb age of the Yongsheng nepheline syenite from southern Jilin Province under different spot sizes. The obtained ages are comparable with that of SHRIMP in both accuracy and precision. The age is also identical to that of the Yinmawanshan gabbro from the Liaodong Peninsula within error. Both the Yongsheng nepheline syenite and the Yinmawanshan gabbro represent the youngest known exposed intrusions in northeastern and even eastern China. The results indicate the Eocene mantle-derived magmatic underplating, and the rapid crustal uplifting of this region since 30 Ma. The analyses also document extremely high LREE concentrations and relatively flat REE patterns for the zircons from the Yongsheng nepheline syenite, which represent a new type of zircon REE pattern.
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The well-preserved seamount buildups are documented from the northwestern Qinling (秦岭) orogenic belts, Northwest China. The study sections are located in the Ganjia (甘加) area of the Xiahe (夏河) County, Gansu (甘肃) Province. The dark basalt and overlying massive reef carbonate characterize the Xiahe seamount buildup. Basalts are dominated by the olivine type of rocks and bear distinct porphyritic textures, and fumarole and amygdaloidal structures. The basalts are dominated by SiO2 (up to 48.49 wt.%–52.29 wt.%) followed by (Na2O+ K2O) (3.80 wt.%–4.96 wt.%) and TiO2 (2.04 wt.%–2.52 wt.%). They are featured by considerably high content of Ti. The tholeiite-series rocks dominate the basalts, while calc-alkali-series rocks are also present. The REE of the basalts shows the LREE-enrichment type with distinct positive Eu abnormal. The trace elements of the basalts are characterized by the lack of P and high content of Ti. These geochemical signals suggest that the Xiahe basalts were formed in an ocean-island setting. The LA ICP-MS zircon U-Pb age of the basalts is 267.6±5 Ma, which is reinforced by the presnce of the fusulinid Neoschwagerina Zone of the Wordian (Middle Permian) in the limestone interbeds of the basalts. Integration of petrological and geochemical studies of seamount basalts and lateral correlation of seamount buildups reveals that the Qinling-Qilian-Kunlun orogenic belts were probably the archipelagic oceans during the Permian.
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