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SHRIMP U-Pb dating and its stratigraphic significance of tuff zircons from Heishan Formation of Kunyang Group, Dongchuan area, Yunnan Province
Abstract
There have been a lot of interests on the formation age of Kunyang Formation and its stratigraphy for a long time, some of the data obtained are referable while there is still a lack of high quality SHRIMP dating. During this time, Sample D0202 in representative of crystal chips and lithic fragments tuff with great stratigraphic significance was collected from middle to upper Heishan Group with a thickness about 180 m in Dongyang Area, Yunnan Province, from which over one hundred zircons were picked out to go through SHRIMP U-Pb dating, at the end, it's indicated that the weighted average age is (1503 ± 17) Ma. Th/U value of Sample D0202 is over 0.48, and it displays a distinct oscillatory zoning structure, which can be regarded as typical magmatic cause, these all indicate that Heishan Formation is formed during Early Mesoproterozoic. This result can further prove that the formation age of Kunyang Group is over 1500 Ma, thus can be provided as an evidence for ascertaining the age and stratigraphy of Kunyang Group.
... For a long time, the stratigraphic division and depositional age of the Dongchuan and Kunyang Groups have been controversial Zhao et al., 2010;Yin et al., 2011a;Gao et al., 2015Gao et al., , 2018. Some scholars believe that the Dongchuan and Kunyang Groups should be constrained to the Mesoproterozoic Sun et al., 2009;Yin et al., 2011a;Gao et al., 2018). However, some researchers hold different views Liu et al., 2018). ...
... Moreover, the age of tuff in the lower strata of the Yinmin Formation is 1742 ± 13 Ma (Zhao et al., 2010), which is not inconsistent with our data. In the Dongchuan region of eastern Yunnan Province, tuff zircon ages of ~1503-1500 Ma were found in the Heishan Formation, which can be compared with the Etouchang Formation (Sun et al., 2009;Li et al., 2013), and the age of diabase in the Yinmin Formation was 1667 + 13 Ma (Zhu et al., 2011b). These data and our results correlate; hence, verifying the credibility and rationality of our data. ...
... Such characteristics are consistent with the results of the detrital zircon Lu-Hf isotopic analysis from the Precambrian sedimentary rock in the Yangtze Block (Li et al., 2012). On the northern margin of the Yangtze Block, there is a chronological record of tectonothermal events related to assembly and breakup of the Columbia supercontinent (Zhang et al., 2006a;Sun et al., 2009;Xiong et al., 2009;Peng et al., 2009;Zhang et al., 2011). Almost all the samples here have a detrital zircon age peak of ~1.86 Ga, which also confirms that strong tectonothermal events in the late Paleoproterozoic period of 2.0-1.85 ...
On the southwestern margin of the Yangtze Block, the Dongchuan Group consists of slightly metamorphosed sedimentary rocks, including silty slate, argillaceous slate, clayey slate, arkose, dolomite, and minor volcanic rocks. To date, it is still a controversy over the depositional age and stratigraphic sequence of the Dongchuan Group. In this study, we analyzed five samples of meta‐sedimentary rocks and one sample of meta‐tuff from the Yinmin, Luoxue and Etouchang Formations of the Dongchuan Group in the Yuxi region for detrital zircon U‐Pb ages and Lu‐Hf isotope. The detrital zircon ages of the meta‐sediments vary from 3073 to 1703 Ma, mainly clustered at three periods, from 1889 to 1840, 2490 to 2008 and 2878 to 2844 Ma. The youngest age peak of all the samples is ∼1859 Ma, with the ∊Hf(t) values of the zircons ranging from –20.3 to +4.3 and more than 90% being negative, indicating that the Paleoproterozoic crustal accretion on the southwestern margin of the Yangtze Block was dominated by reworking of the ancient crustal materials involved in the assembly and breakup of the Columbia supercontinent. Another important age range is between 2490 Ma and 2008 Ma, with ∊Hf(t) values from –14.7 to +8.9 and 70% of them are negative, suggesting that the magmatism in the source area was also dominated by reworking and recycling of the ancient crustal materials, with minor juvenile mantle substances added. The detritus was probably derived from the Paleoproterozoic crystalline basement in the southern Yuxi region. The oldest peak age is ∼2847 Ma and the ∊Hf(t) values are from –7.7 to +7.0 with 50% of both positive and negative values, demonstrating a possible ∼2.85 Ga ancient continental nucleus on the southwestern margin of the Yangtze Block and substantial growth in juvenile crust materials during this period. Besides, the weighted average age of the zircons from the meta‐tuff of the Etouchang Formation is 1677 ± 14 Ma. Combining the previous research data and this study, we can constrain the depositional age of the Dongchuan Group in central Yunnan Province to the period from the late Paleoproterozoic to early Mesoproterozoic, slightly earlier than that of the Dongchuan Group in the Dongchuan area near to the southwestern Sichuan Province. The depositional age of the Dongchuan Group is older than that of the Kunyang Group.
... Hekou groups of the southwestern Yangtze Block (Fig. 9), which is widely regarded as connected to northwestern Laurentia, Siberia and northern Australia (Greentree et al., 2006;Sun et al., 2009;Zhao et al., 2010;Yang et al., 2012;Chen et al. 2013;. proposed that the Yangtze Block was connected with the northwestern part of Laurentia, then drifted away on or before ca. ...
... 1.50 Ga to 1.38 Ga propagated northward, based on paleomagnetic data. Thus, considering the fact that the Baoban Group was deposited at 1460-1430 Ma and given its connection with the Belt- Fig. 9. Zircon U-Pb age spectra comparisons amongst (a) Cathaysia Block (Yu et al., 2009;Chen et al., 2018); (b) Yangtze Block (Greentree et al., 2006;Sun et al., 2009;Zhao et al., 2010;Yang et al., 2012;Chen et al. 2013;; (c) Northwest Laurentia (Medig et al., 2014), (d) West Laurentia (Anderson and Davis, 1995;Doughty and Chamberlain, 1996;Sears et al., 1998;Evans, et al., 2000;Lewis et al., 2010) and (e) Hainan Island (Li et al., 2002(Li et al., , 2008Yao et al., 2017;Zhang et al., 2017Zhang et al., , 2018; this study). ...
The Mesoproterozoic Baoban Group is the oldest basement in Hainan Island and has played an important role in Columbia (Nuna) supercontinent reconstructions. The Mesoproterozoic granitic intrusions in the Baoban Group are the most widely‐exposed Precambrian magmatic rocks and are the key to understanding the tectonic settings of Hainan Island and its relationship with the South China Block and the Columbia supercontinent. New LA‐ICP‐MS zircon U‐Pb dating on three mylonitic granite samples from the Tuwaishan and Baoban areas yield ages ranging from 1447 Ma to 1437 Ma, representing the absolute timing of the emplacement of the granitic intrusions. Combined with previously published geochronological data for rocks from the Baoban Group and regional mafic intrusions, it is concluded that the Baoban Group formed at 1460–1430 Ma, coeval with the emplacement of the granitic and mafic intrusions. New in‐situ zircon Lu‐Hf isotope analyses for the three mylonitic granite samples yielded positive ∊Hf(t) values, ranging from +0.49 to +8.27, with model ages (TDMC) ranging from 2181 Ma to 1687 Ma, suggesting that the granitic intrusions originated from a mixed source of Paleoproterozoic crust with juvenile crust. New zircon trace element data show characteristics of high Th/U values of 0.24–1.50, steep slopes from LREE to HREE and negative Pr, Eu anomalies with positive Ce, Sm anomalies, representing typical magmatic zircons formed in continental crust. Compared with available magmatic and detrital zircon ages from Precambrian rocks in the Cathaysia Block, Yangtze Block and western Laurentia, it is inferred that Hainan Island was separated from both the Cathaysia Block and the Yangtze Block, instead being connected with western Laurentia in the Columbia supercontinent. Considering the decreasing tendency of basin deposition time along the western margin of Laurentia, it is proposed that Hainan Island was located to the north or northwest of the Belt‐Purcell Supergroup, along the western margin of Laurentia, during the breakup of the Columbia supercontinent.
... The late Paleoproterozoic to earliest Mesoproterozoic strata, composed of greenschist-to amphibolitefacies metamorphic volcano-sedimentary rocks, are widely distributed in the southwestern Yangtze Block (Fig. 1b). Metavolcanic rocks yielded zircon U-Pb ages ranging between 1.75 and 1.50 Ga (Greentree and Li, 2008;Sun et al., 2009a;Zhao et al., 2010;Chen et al., 2013;Geng et al., 2017;Li et al., 2013) and were intruded by synchronous or slightly younger mafic dykes and granites (Zhao et al., 2010;Chen et al., 2013;Fan et al., 2013;Ren et al., 2017;Liu et al., 2019b;Lu et al., 2019). Regionally, they are in fault contact with the late Mesoproterozoic Huili and Kunyang groups (Li et al., 1988;Zhao and Cawood, 2012;Zhou et al., 2014;Geng et al., 2017) (Fig. 1b). ...
... In the southwestern Yangtze Block, intense rift-related magmatic events occurred during 1.75-1.50 Ga and are dominated by mafic dykes and tuffs with some granites and albitites (e.g., Sun et al., 2009a;Zhao et al., 2010;Chen et al., 2013;Fan et al., 2013;Li et al., 2013). They may be the source rocks for these~1.64 ...
The Huili Group, one of the most representative late Mesoproterozoic strata in the Yangtze Block, bears key information for the tectonic history of the South China Block in the context of the supercontinent cycle. We present an integrated dataset involving field observation, petrology, detrital zircon U-Pb dating, and Hf isotope analyses for the Huili Group. Our new detrital zircon U-Pb ages, in combination with available magmatic age data, confirm that the Huili Group was mainly deposited at ca. 1.1-1.0 Ga. The lower Huili Group is characterized by subrounded to rounded detrital zircon grains with age intervals of 2.80-2.40 Ga (~21%), 2.34-1.72 Ga (~64%), and 1.68-1.19 Ga (~14%). In contrast, zircon grains from the upper Huili Group have variable morphologies and yield two pronounced age populations of 2.00-1.25 Ga (~50%; subrounded to rounded grains) and 1.2-1.0 Ga (~46%; euhedral to subhedral grains). The majority of zircon grains have εHf(t) values and depleted mantle two-stage (TDM2) model ages comparable to those of magmatic rocks or older sediments in the Yangtze Block. Multiple sources are suggested to have contributed older detrital zircon grains to the lower Huili Group, whereas the upper part received greater proportions of zircon grains with ages close to or equal to the depositional age from proximal magmatic sources. This observation indicates a drastic provenance shift most likely occurred within the Huili Group at ~1.04 Ga. Through reappraising our detrital zircon results and available geological datasets, we suggest that the terrigenous clastic and carbonate rocks of the lower-middle Huili Group were deposited on a passive continental margin, but the upper volcano-sedimentary sequences were formed in a back-arc extensional setting. We further propose that the Yangtze Block was spatially separated from (i.e., not yet part of) the Rodinia supercontinent during the sedimentation of the Huili Group, supporting that a global supercontinent did not exist yet in the late Mesoproterozoic.
... Dolostone from the Luoxue Formation yields a SHRIMP Pb-Pb isochron age of 1716 ± 56 Ma (Chang and Zhu, 2002). Tuff sampled from the E'touchang Formation yields a SHRIMP zircon U-Pb age of 1503 ± 17 Ma (Sun et al., 2009). This disparate 200 m.y. ...
... A sample of a felsic volcanic unit from the Tianbaohsan Formation at the top of the group yields a SHRIMP zircon U-Pb age of (Mou et al., 2003) 1028±9 Ma (Geng et al., 2007) 1494±6,1486±3 & 1490±4 Ma 1513±21 & 1531±18 Ma (Geng et al.,2012) 1694±16 Ma (Wang et al.,2013) 1032±9 Ma (Zhang et al., 2007) 1258±70 Ma (Chang et al., 2002) 1503±17 Ma (Sun et al., 2009) 1742±13 Ma 1716±56 Ma (Chang et al., 2002) 1659±16 Ma (Zhao & Zhou, 2011) 1686±4 & 1711±4 Ma (Yang et al.,2012) 1680±13 Ma 1695±20 Ma (He, 2009) 1710±8 Ma (Guan et al., 2011) Hekou Group 995±15 Ma (Greentree et al., 2006) Fengshan Fm 1675±8 Ma (Greentree & Li, 2008) ...
The Yinachang Fe-Cu-Au-U-REE deposit is hosted by the lower part of the Paleoproterozoic Kunyang Group in the central Yunnan Province of SW China in an area known to contain iron-oxide Cu-Au mineralisation. The deposit includes: (i) the sulphide assemblage chalcopyrite – pyrite – magnetite – cobaltite – molybdenite – cassiterite; (ii) Rare Earth Element assemblage bastnaesite – parasite – fergusonite – xenotime – monazite; (iii) the uranyl hydroxide mineral vandendriesscheite; (iv) gold commonly hosted by ankerite; and (v) the gangue mineral assemblage apatite – biotite – fluorspar – quartz – calcite. The ore is commonly massive, disseminated, banded, or in calcite veins. The banded mineralisation contains high concentration of Au, Co, Mo, U, Fe, Cu and REE, and the vein-type mineralisation has abundant REE minerals of bastnaesite, parisite, fergusonite and xenotime. Monazite exists as inclusions in apatite or as discrete grains on the surface of magnetite, and the uranium is associated with chalcopyrite. The mineralising process can be divided into an initial Na-alteration followed by the ore-forming assemblages of Fe-REE and Cu-Au-U-REE mineralisation. The average δ¹⁸OH2O values in the quartz and calcite change are between 3.5 and 10.7‰, with δDV-SMOW values ranging between −98.2 and −47.7‰. The calcite, siderite and ankerite have δ¹³C isotope composition ranges from –14 to +1‰ and δ¹⁸O compositions of +6.9 to +22‰. The H–O–C isotope systematics indicate that the mineralising fluids have mixed magmatic and metamorphic sources, whereas the carbon is sourced from marine carbonate, and the low temperature alternation of polyphase mantle material. In situ δ³⁴S sulphide value ranges between 1.1 to 11.9‰, and the bulk δ³⁴S value ranges between -4.7 and 10.5‰. In situ Pb isotopes of sulphide samples have ²⁰⁶Pb/²⁰⁴Pb values of 18.58–18.76, ²⁰⁷Pb/²⁰⁴Pb values of 15.51–15.66 and ²⁰⁸Pb/²⁰⁴Pb values of 37.47–38.06. These values plot in the upper crust Pb-evolution curve, indicative of a complex source of Pb in the deposit. The Pb is interpreted to have a deep-seated magmatic source with a contribution from the crust. It is also proposed that the REE-mineralised fluids are derived from a late stage of alkaline magma differentiation. The ⁴⁰Ar-³⁹Ar biotite date indicates that the Precambrian rocks in the Kangdian region were regionally metamorphosed at ca. 900 Ma. The Yinachang Fe-Cu-Au-U-REE deposit is interpreted as an IOCG deposit based on geological and isotopic studies. The banded ore and vein type ore are the main exploration targets for uranium, gold and REE. This study helps us better understand IOCG deposits in China.
... experienced several mineralization and hydrothermal events as follows: (1) the earliest main mineralization at ~1.6-1.67 Ga, which is nearly synchronous with host rock (ages: ~1.6-1.7 Ga [6][7][8]10,39,51,59,118]); (2) a local hydrothermal overprint at ~1.45 Ga, which is related to early Mesoproterozoic magmatism (age: ~1.5 Ga [54,62,119]); (3) a second major mineralization at ~1.3 Ga, which may have been caused by volcanism (age: 1270 ± 95 Ma [20]); (4) the third major mineralization at ~1.1-1.0 Ga, which is closely associated with late Mesoproterozoic magmatism (ages: 1142-1208 Ma [19][20][21]52,120]); (5) the fourth major mineralization at ~0.8 Ga, which is a newly identified main mineralization event in the Kangdian copper belt, and likely related to the Neoproterozoic magmatism (ages: ~850 Ma [15,113,114]) and/or metamorphism (ages: ~850 Ma [15,113,114]). ...
... Ga, which is nearly synchronous with host rock (ages:~1.6-1.7 Ga [6][7][8]10,39,51,59,118]); (2) a local hydrothermal overprint at~1.45 Ga, which is related to early Mesoproterozoic magmatism (age:~1.5 Ga [54,62,119]); (3) a second major mineralization at~1.3 Ga, which may have been caused by volcanism (age: 1270 ± 95 Ma [20]); (4) the third major mineralization at~1.1-1.0 ...
The Hongnipo deposit, a newly discovered large copper deposit in the Kangdian copper belt, SW China, is hosted in the Paleoproterozoic Hekou Group. This deposit contains ~4200 Mt of Cu ores, with an average grade of 1.42 wt.% Cu. Orebodies occur mainly as stratiform, stratoid and lenticular forms. Mineralization consists predominantly of high grade vein-type ores and low grade laminated ores. Field relationships indicate vein-type mineralization crosscuts laminated mineralization and host rocks, indicating that there were at least two mineralization events during the formation of the deposit. Pyrite separates from the laminated ores yield a Rb-Sr isochron age of 1552 ± 80 Ma, with a highly radiogenic initial ⁸⁷Sr/⁸⁶Sr ratio of 0.71214 ± 0.00081, indicating a major contribution from the ore-hosting rocks. Sulfides from the laminated ores have δ³⁴S values ranging from −1.8‰ to 11.4‰, with the vast majority in the range of 5.3‰ to 11.4‰, suggesting the mixed derivation of sulfur from seawater sulfates and magmatic fluids. Chalcopyrite separates from the vein-type ores have a Re-Os isochron age of 794.8 ± 7.9 Ma. The initial ¹⁸⁷Os/¹⁸⁸Os (2.8 ± 1.2) and γOs (+2202) values are slightly lower than the average values of continental crust, indicating a major metal source of the Hekou Group with minor mantle input. Sulfides from the vein-type ores have δ³⁴S values that range from −10.3‰ to 4.0‰ and cluster between 0‰ to 2.2‰, which implies a significant contribution of magmatic-sourced sulfur with minor biogenic sulfur. Two major mineralization events have been identified. The Rb-Sr age of the laminated ores likely records a VMS mineralization event at ~1.6 Ga. The much younger Re-Os age is considered to represent the timing of an important mineralization event, which is likely related to the Neoproterozoic magmatism and/or metamorphism and represents a newly documented mineralization event to be targeted by exploration.
... Volcanic layers from the Dahongshan and Hekou Groups have zircon U-Pb ages of 1.68 Ga ( Greentree and Li, 2008;Zhao and Zhou, 2011) and 1.7 Ga ( Chen et al., 2013), respectively. Zircons from lower and upper tuff layers of the Dongchuan Group yield ages of 1.7 Ga and 1.5 Ga ( Sun et al., 2009;Zhao et al., 2010). These three groups were thought to be lateral equivalents in different parts of the area ( Zhao et al., 2010). ...
... Numerous Proterozoic plutons intruding those groups are ~1.7 Ga and ~1.0 Ga rift-related mafic-felsic rocks and ~860-740 Ma mafic-intermediate-felsic rocks (e.g., Greentree and Li, 2008;Zhao et al., 2010;Zhou et al., 2014;Zhu et al., 2016). Sparse ~1.5 Ga mafic bodies and volcanic counterparts were also reported in the northern part of the region ( Sun et al., 2009;Fan et al., 2013). ...
The Dahongshan Fe-Cu ore deposit, hosted in the Paleoproterozoic meta-volcanic and meta-sedimentary sequences, is a giant deposit in the Fe-Cu metallogenic province of southwestern China. Two ore types have been identified: (1) massive and disseminated Fe ores hosted dominantly in meta-volcanic rocks and (2) disseminated and banded Fe-Cu ores in meta-sedimentary rocks. Magnetite presents in all orebodies, and is dominant in the Fe ores. Chemistry of magnetite suggest that the fluids for iron mineralization in the Fe and Fe-Cu orebodies are likely chemically similar and cogenetic. Minor sulfides (e.g., molybdenite) occur at the end of iron mineralization stage, indicating the gradually decrease in oxygen fugacity for the mineralizing fluids with magnetite precipitation. Along with evolution, mineralizing fluids generate magnetite with depletions in Cr, Ni, Ga and V, but enrichments in Mn, Sn and Co, which are primarily reflective of the temperature decrease of fluids.
We have discovered some magnetite grains that are extremely rich in V (~10000 ppm), but low in Ti and Cr. Geochemical patterns suggest that they were formed by fluids similar to those of ordinary ores. Available knowledge about the unique high-V magnetite indicates highly-reduced marine environments for its generation. Ore bulk REE patterns showing remarkable positive Eu anomalies and absence of obvious Ce anomalies suggest a BIF-like marine environment, consistent with the morphology of both Fe and Fe-Cu orebodies. Our results provide independent evidence for submarine environment in the formation of the giant Precambrian stratiform Fe(-Cu) ore deposit.
... Numerous explosive volcanic breccias, which are thought to be associated with the generation of giant Fe-Cu deposits that represent targets for mineral exploration in the southwestern Yangtze Block (Chen and Zhou, 2012;Zhao et al., , 2017Zhou et al., 2014;, erupted through, and are mainly hosted in, the Yinmin and lower Luoxue formations (Zhao et al., 2010). The depositional time of the Luoxue Formation is bracketed between 1676 ± 13 Ma, as constrained by an U-Pb zircon crystallization age of a dolerite intruding into the Yinmin Formation and lower part of the Luoxue Formation (Zhu et al., 2011), and 1503 ± 17 Ma, an U-Pb zircon age derived from a volcanic tuff in the overlying Etouchang Formation (Sun et al., 2009b) (Fig. 2). ...
... Samples are indicated to the right of the column. Zircon U-Pb age data for volcanic interlayer and mafic intrusion are also presented (Sun et al., 2009b;Zhao et al., 2010;Zhu et al., 2011). ...
Bulk rock elemental, C, O and Sr isotopic data for carbonates of the Palaeoproterozoic to Mesoproterozoic Luoxue and Luzhijiang formations from the southwestern margin of the South China Block are studied to infer aspects of the provenance and depositional environment. Elemental tracers demonstrate that the upper Luoxue and Luzhijiang carbonates were not significantly affected by crustal contamination and diagenetic/metamorphic overprinting, thus preserving their primary chemical signature, which is also consistent with the preservation of primary sedimentary structures and textures. In contrast, C, O and Sr isotopes of the lower Luoxue carbonates appear to have been variably altered by ore-forming fluids. All the Luoxue carbonates lack enrichment of Y, corresponding to chondritic Y/Ho ratios of 25–31, in contrast to modern seawater and marine carbonates. Shale-normalized REE + Y patterns for the Luoxue carbonates show pronounced enrichment in middle REE, but lack strong elemental anomalies (La, Gd, Y). Based on petrographic and sedimentological characteristics, the Luoxue Formation was probably formed in a shallow water, epicontinental basin with restricted but variable exchange to the open ocean, and dominant terrigenous input. The Luzhijiang carbonates, on the other hand, are pure chemical sediments devoid of detrital material, and shale (PAAS) normalized REE + Y distributions exhibit positive La, Gd, and Y (Y/Ho: 39–47) anomalies, which are typical features of marine waters throughout the Archean and Proterozoic periods. ⁸⁷Sr/⁸⁶Sr values in both the upper Luoxue and Luzhijiang carbonates are significantly higher than coeval seawater, indicative of enhanced contribution from weathered continental sources. This increased influx from terrestrial sources very likely corresponds to the break-up of the hypothesized Columbia/Nuna supercontinent, as the Luoxue and Luzhijiang carbonates were deposited in a rift-related basin associated with supercontinental fragmentation.
... Data sources: 1.75-1.5 Ga volcanic rocks and intrusions (Hu et al., 1991;Sun et al., 2009;Zhao et al., 2010;Zhao and Zhou, 2011;Chen et al., 2013;Fan et al., 2013;Ye et al., 2013;Guo et al., 2014;Hou et al., 2015;Pang et al., 2015;Zhu et al., 2017;Zhu et al., 2018), 1.18-1.14 Ga A type granitoids in southwestern Yangtze Block (Greentree et al., 2006;Greentree, 2007;Li et al., 2013;Wang et al., 2014;Huang et al., 2021;Li et al., 2021Li et al., , 2022, 1.04-1.0 ...
... The zircons in the Panzhihua gabbro yield a weighted mean age of 1841 ± 34 Ma in southern Sichuan , and those in the Yimen tonalite yield a weighted mean age of 2433.1 ± 9.7 Ma in central Yunnan . Furthermore, granites, whose ages are consistent with the subordinate age peak values of sample QJP-29-R-2, are sporadically exposed in the Kangdian paleohigh region (Sun et al. 2009;Zhu et al. 2011;Liu et al. 2018;Ning et al. 2021). The positive and negative ε Hf(t) values and T DM2 ages in sample QJP-29-R-2 suggest that the protoliths were mainly sourced from mixed Archaean-Proterozoic crust-mantle materials. ...
The Emeishan large igneous province (ELIP) is among the prominent large igneous provinces in the world and has been associated with mantle plume activity. In this study we investigated the impact of the Emeishan mantle plume on generating the sedimentary rock suites of the eastern Sichuan Basin. We present petrology, detrital zircon U-Pb ages, trace elements, and Hf isotopic compositions of the Middle-Late Permian sedimentary sequences in the Huayingshan region to constrain the provenance and characterize the depositional response to the Emeishan mantle plume activity. The detrital zircon U-Pb ages of the Middle Permian Maokou Formation indicate that terrigenous detritus was mainly sourced from the Kangdian paleoland in the southwestern margin of South China. Detrital zircon grains from the bottom of the Late Permian Longtan Formation yield a lower intercept age of 257 ± 28 Ma, interpreted as the contemporaneous metamorphism related to the ELIP magma. The detrital zircon U-Pb ages of the middle part of the Longtan Formation are characterized by unimodal age spectra with a peak at 259 Ma. Provenance analysis indicates that the Longtan Formation was mainly sourced from the Emeishan volcanic rocks in the Huayingshan region. We propose that the Kangdian paleohigh may have been regionally uplifted as the result of the pre-eruption rise of the Emeishan mantle plume in the late Middle Permian. Moreover, this paleohigh was translated into a denuded zone and provided voluminous detritus into the eastern Sichuan Basin. In the early Late Permian, the ELIP magmas upwelled and outpoured from the Huayingshan fault, and flowed past the peripheral rocks to the low terrain in the Huayingshan region. The ELIP volcanic rocks in the Huayingshan region underwent intense post-eruption erosion, resulting in the deposition of voluminous volcanic detritus in the eastern Sichuan Basin. ARTICLE HISTORY
... These Paleoproterozoic strata are composed of weakly metamorphosed siliciclastic and dolomitic rocks with minor interbedded volcanic rocks. Volcanic rocks from the Heishan Formation in the upper section of the Dongchuan Group contain zircon with U-Pb ages of ~1.5 Ga and are significantly younger than the lower roots of this group (Sun et al., 2009;Li et al., 2013). Mafic magmatism between 1486 and 1531 Ma produced Fe-Ti-V oxide-bearing intrusions in Tongan, the northern part of the Kangdian region, which is suggestive of a prolonged continental rift setting (Geng et al., 2012;Fan et al., 2013). ...
Precambrian iron oxide copper-gold (IOCG) deposits are generally encountered with multistage hydrothermal overprints and hence have complex isotopic records. Precise dating of ore-forming and overprinting events and assessment of time-resolved metal sources are fundamental for understanding ore genesis. Here, we quantify the evolution history by integrating in situ U-Pb dating of texturally constrained allanite and Sm-Nd isotope data of ores and major rare earth element (REE) minerals in the breccia-hosted Lanniping Fe-Cu deposit in Kangdian region, southwestern China.
The economically mineralized breccia in Lanniping Fe-Cu deposit is characterized by pervasive and texturally destructive replacement of polymictic clasts, including host metasedimentary packages, the intruded dolerite, and pre-ore halokinetic breccia. Ore minerals in cements are mainly composed of magnetite, chalcopyrite, bornite, and variable amounts of REE-rich minerals (e.g., apatite and allanite/epidote). Two types of allanite were identified in ores. Type I prismatic allanite texturally intergrown with magnetite has a SHRIMP U-Pb age of 1728 ± 20 Ma (1σ), which matches a zircon U-Pb age of 1713 ± 14 Ma (2σ) for the dolerite clasts and provides the direct age constraint on the Fe-Cu mineralization event. Type II anhedral allanite shows complex zoning and is spatially associated with, but texturally later than, magnetite, apatite, and chalcopyrite. This type of allanite yields significantly younger SHRIMP dates of 1015 ± 33 (1σ) and 800 ± 16 Ma (1σ) for cores and rims, respectively, which correspond to discrete regional magmatic events and hence record hydrothermal overprint/remobilization events of ore minerals in the deposit.
Integrated Sm-Nd isotope compositions of type I allanite, apatite, and whole ores generally align along the reference Sm-Nd isochron of 1728 Ma, further confirming the primary ore formation at ~1.7 Ga. Corresponding εNd(1728 Ma) values ranging from –2.8 to 0.3 are significantly higher than those of the host metasedimentary rocks (–9.5 to –6.2) but comparable to those of contemporaneous igneous intrusions (–0.3 to 5.3) in the region, demonstrating that REE components of the primary ores were dominantly sourced from rocks of mantle-derived affinity. Both cores and rims of the younger type II allanite grains have Nd isotope compositions consistent with the unique time-evolved line of the ~1.7 Ga ores, implying that REEs incorporated into type II allanite were ultimately sourced from the primary ores in this deposit. The combined texture, chemical, U-Pb, and Sm-Nd isotope data thus demonstrate that REE remobilization was localized during post-ore hydrothermal overprint with negligible external inputs of REEs to the primary ores in the Lanniping deposit.
In this contribution, we not only date primary ore formation but also recognize several younger allanite generations that record internal metal redistributions in response to post-ore tectonothermal events. Our study highlights the potential of ore-associated REE minerals such as allanite for resolving the age of multiple stages of hydrothermal events in complex ore deposits by ion probe, provided that careful examination of textural and paragenetic relationship of ores is conducted. Our finding of these younger allanite generations also exemplifies the significance of evaluation on time-resolved metal input for better characterizing the evolution history of the IOCG deposits.
... The Mesoproterozoic to early Neoproterozoic folded basements are widely distributed in the western Yangtze Block, including the groups of Dongchuan (~1.7-1.5 Ga) and Kunyang/Huili (~1.2-0.9 Ga), as well as equivalents (Yan et al., 2003;Sun et al., 2008Sun et al., , 2009Zhao et al., 2010;Wang et al., 2012), which mainly consist of greywacke, slate, and carbonaceous and siliceous sedimentary rocks (Zhou et al., 2014a;Hu et al., 2017b;Zhou et al., 2018a). The cover successions are mainly composed of Ediacaran to early Mesozoic (Triassic) marine and late Mesozoic (Jurassic) to Quaternary continental sedimentary rocks (such as carbonate and clastic rocks), as well as late Permian basalts of the Emeishan large igneous province (Liu and Lin, 1999;Zhou et al., 2002;Zhou et al., 2013a;Hu et al., 2017a). ...
The Maoping Devonian and Carboniferous carbonate-hosted epigenetic Pb-Zn deposit, a typical representative of multi-layer (two or more than two ore-bearing strata) Pb-Zn metallogenesis, is located in the central Upper Yangtze Pb-Zn metallogenic province, which consists of >400 carbonate-hosted Pb-Zn deposits (spots) accounting for at least a quarter of total Pb and Zn reserves in China. The Maoping deposit is the second largest one in the province and contains ∼30 Mt ores with grades of Pb + Zn ranging from 15 wt. % to 35 wt. %. A total of three ore bodies (groups) as layers, lens or veinlets are distributed in the NW-trending inverted wing of the Maomaoshan anticline and its secondary NE-trending bedding fracture. Nos. I, II and III ore bodies (groups) are hosted by dolostone of the late Devonian Zaige Fm., early Carboniferous Baizuo Fm., and late Carboniferous Weining Fm., respectively. Sphalerite, galena and pyrite are the most abundant sulfide minerals, while dolomite, calcite, quartz and barite are gangue minerals. These minerals have a massive, disseminated or veined structure, and a granular, metasomatic, co-edge, colloidal, aggregate or fragmentation texture, suggesting an epigenetic origin. NanoSIMS in-situ sulfur isotope analysis shows that the δ³⁴S values of sulfides ranging from -20.4‰ to +25.7‰, of which the pyrite framboid and colloidal sphalerite have δ³⁴S values ranging from -20.4‰ to -8.7‰, and the δ³⁴S values of euhedral granular pyrite and xenomorphic granular sphalerite vary from +22.1‰ to +25.7‰. Such sulfur isotope signatures indicate that the formation of S²⁻ in ore-forming fluids has undergone both marine bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR) processes. The processes of BSR and TSR are chiefly temperature depended, so the reduction of sulfate in the Maoping deposit is most likely to occur at the local and may first undergo a relatively low temperature’s BSR process, then goes through a relatively high temperature’s TSR process. LA-MC-ICPMS in-situ Pb isotope analysis shows that the Pb isotopic ratios of galena are relatively uniform and ²⁰⁶Pb/²⁰⁴Pb=18.707-18.773, ²⁰⁷Pb/²⁰⁴Pb=15.780-15.802 and ²⁰⁸Pb/²⁰⁴Pb=39.375-39.530. Such Pb isotope signatures indicate that the source of Pb is single or well-mixed. After comparing with all the potential metal source rocks, we implied that the metals in the Maoping deposit were mainly derived from wall rocks with a certain contribution from basements and basalts. In addition, the in-situ Pb isotopic ratios increase as altitude increases (from 720 to 760m), which suggests that the migration of metal-bearing fluids is most likely to go upward, and with the evolution of hydrothermal system, the contribution of radiogenic Pb-depleted basements and basalts was declining. This paper proposed that (i) Pb-Zn ores do not select strata, but are selective for lithology, (ii) various processes are responsible for the ore formation at Maoping, including BSR and TSR, fluids mixing and sulfide rapid precipitation, and (iii) the multi-layer metallogenesis of the Maoping carbonated-hosted epigenetic Pb-Zn deposit is a coupling mineralization product of ore-forming fluids, trapped structures and favorable lithologies, which is different from that of typical Mississippi Valley-type (MVT) deposits.
... The oldest sedimentary unit recognized in the assembled proto-Yangtze Block is the Dongchuan Group of siliciclastic, carbonate and minor volcanic rocks metamorphosed to upper greenschist to lower amphibolite facies. Interstratified tuffs constrain the depositional age to between 1742 Ma and 1503 Ma (Sun et al., 2009b;Zhao et al., 2010; and U-Pb zircon ages of the interstratified volcanic rocks in each group, along with intrusive dykes and granites, which fall in the range of ca. 1050-1020 Ma (Geng et al., 2007;Yin et al., 2012;Chen et al., 2014;Zhu et al., 2016;Chen et al., 2018;Wang et al., 2019). ...
Contrasting models for internal and external locations of South China within the Nuna and Rodinia supercontinents can be resolved when the current lithotectonic associations of Mesoproterozoic and older rocks units that constitute the craton are redefined into four lithotectonic domains: Kongling, Kunming-Hainan, Wuyi, and Coastal. The Kongling and Kunming-Hainan domains are characterized by isolated Archean to early Paleoproterozoic rock units and events and crop out in northern and southern South China, respectively. The Kunming-Hainan Domain is preserved in three spatially separated regions at Kunming (southwestern South China), along the Ailaoshan shear zone, and within Hainan Island. Both domains were affected by late Paleoproterozoic tectonothermal events, indicating their likely juxtaposition by this time to form the proto-Yangtze Block. Late Paleoproterozoic and Mesoproterozoic sedimentary and igneous rock units developed on the proto-Yangtze Block, especially in its southern portions, and help link the rock units that formed along the shear zone at Ailaoshan and on Hainan Island into a single, spatially unified unit prior to Paleozoic to Cenozoic structural disaggregation and translation. The Wuyi Domain consists of late Paleoproterozoic rock units within a NE-SW trending, fault-bounded block in eastern South China. The Coastal Domain lies east of the Wuyi domain and is inferred to constitute a structurally separate block. Basement to the domain is not exposed, but zircon Hf model ages from Mesozoic granites suggest Mesoproterozoic basement at depth.
The Archean to Paleoproterozoic tectonothermal record of the Kongling and Kunming-Hainan domains corresponds closely with that of NW Laurentia, suggesting all were linked, probably in association with assembly and subsequent partial fragmentation of the Nuna supercontinent. Furthermore, the age and character of Mesoproterozoic magmatism and detrital zircon signature of sedimentary rocks in the proto-Yangtze Block matches well with western Laurentia and eastern Australia-Antarctica. In particular, the detrital zircon signature of late Paleoproterozoic to early Mesoproterozoic sedimentary units in the block (e.g. Dongchuan Group) share a similar age spectrum with the Wernecke Supergroup of northwest Laurentia. This, together with similarities in the type and age of Fe-Cu mineralization in the domain with that in eastern Australia-Antarctica, especially northeast Australia, suggests a location adjacent to northwest Laurentia, southern Siberia, and northeast Australia within the Nuna supercontinent.
The timing and character of late Paleoproterozoic magmatic activity in the Wuyi domain along with age of detrital zircons in associated sedimentary rocks matches the record of northern India. During rifting between Australia–Antarctica and Laurentia in the late Mesoproterozoic, the proto-Yangtze Block remained linked to northeast Australia. During accretionary orogenesis in the early Neoproterozoic, the proto-Yangtze Block assembled with the Wuyi Domain along the northern margin of India. The Coastal domain likely accreted at this time forming the South China Craton. Displacement of the Hainan and Ailaoshan assemblages from southwest of the Kunming assemblage likely occurred in the Cenozoic with the activation of the Ailaoshan-Red River fault system but could have begun in the early to mid-Paleozoic based on evidence for tectonothermal events in the Hainan assemblage.
... The basement comprises mainly the Mesoproterozoic to Neoproterozoic Kunyang Group, which consists dominantly of sandstone, siltstone, slate, shale and dolostone with minor volcanic rocks (Li et al., 1984) and has experienced greenschist facies metamorphism. Some authors consider that the Kunyang Group was deposited in a foreland basin setting (e.g., Sun et al., 2009;Li et al., 2013). The overlying cover strata are made up of Neoproterozoic Ediacaran to Middle Triassic shallow submarine carbonate and clastic sedimentary sequences in a passive continental margin. ...
... In particular, drill cores from the Dahongshan ore district also show a series of migmatites with granoblastic texture beneath the Dahongshan Group (Qian and Shen, 1990). The equivalents of the Dahongshan Group in the region are the Dongchuan and Hekou Groups, whose depositional time has been defined as late Paleoproterozoic based on abundant precise zircon U-Pb ages (e.g., Sun et al., 2009b;Zhao et al., 2010;Chen et al., 2013b;Li et al., 2013;Zhu et al., 2018). Regionally, these strata are in fault contact with the Kunyang and Huili Groups (Li et al., 1988). ...
... In particular, drill cores from the Dahongshan ore district also show a series of migmatites with granoblastic texture beneath the Dahongshan Group (Qian and Shen, 1990). The equivalents of the Dahongshan Group in the region are the Dongchuan and Hekou Groups, whose depositional time has been defined as late Paleoproterozoic based on abundant precise zircon U-Pb ages (e.g., Sun et al., 2009b;Zhao et al., 2010;Chen et al., 2013b;Li et al., 2013;Zhu et al., 2018). Regionally, these strata are in fault contact with the Kunyang and Huili Groups (Li et al., 1988). ...
The early Paleoproterozoic is an essential period for understanding the early tectonic evolution of the Yangtze Block and its reconstruction in the Columbia supercontinent, whereas these issues are largely unknown due to the scarce preservation of early Paleoproterozoic geological records. This study presents rarely reported early Paleoproterozoic granitoids from the southwestern Yangtze Block, with integrated studies of zircon U-Pb ages, Lu-Hf isotopic compositions and whole-rock geochemistry. Magmatic zircon U-Pb dating for two monzogranite samples yields weighted mean 207Pb/206Pb ages of 2359 ± 16 Ma and 2363 ± 16 Ma, providing unambiguous evidence for the presence of early Paleoproterozoic magmatism in the Yangtze Block. All the samples have high A/CNK values of 1.30-1.61, typical of S-type granite. These rocks have low total REE contents of 72.5-139 ppm with marked enrichment in LREEs ((La/Yb)N = 10.73-23.83) and conspicuously negative Eu anomalies (Eu/Eu* = 0.46-0.55). The rocks exhibit uniform primitive mantle-normalized trace element patterns with enrichment in Rb, Th, U and Pb and depletion in Sr, Nb, Hf and Ti. These dated zircon grains have consistent negative εHf(t) values of -6.2 to -2.8 and TDM2 ages of ca. 2.97-3.16 Ga, indicative of Mesoarchean crustal materials as their magma source. Considering the existence of the ca. 2.36 Ga regional high-grade tectono-metamorphic event, we propose that the ca. 2.36 Ga monzogranites were most likely generated in the early stage of post-collisional extension. Therefore, the southwestern Yangtze Block likely experienced a collision event during ca. 2.40-2.36 Ga, indicative of the involvement of the Yangtze Block in the ca. 2.5-2.3 Ga Arrowsmith orogeny of Laurentia. In addition, a series of accretionary events might also have occurred in the western Yangtze Block before the final assembly of the Columbia supercontinent, implying a tight spatial connection between the Yangtze Block and northwestern Laurentia within this global-scale supercontinent.
... 1742-1503 Ma) volcanosedimentary sequences, known as the Dongchuan, Dahongshan and Hekou groups (Wang et al., 2014a;Wang and Zhou, 2014), could be probably correlated with the Tianli Schists. The volcanic rocks free Etouchang Formation (> 1503 Ma, Sun et al., 2009) of the middle Dongchuan Group mainly consists of calcareous and arenaceous mudstone, lithologically similar to the primary rocks for calc-and quartz schist, the major litho-units of the Tianli Schists. Similar to the Tianli Wang et al. (2010Wang et al. ( , 2012 and Wang and Zhou (2012). ...
Meso- to Neoproterozoic sedimentary successions along the southeastern margin of the Yangtze Block in South China have been investigated for their depositional ages, provenance and tectonic setting. The 1524 Ma, 834 Ma and 763 Ma U-Pb ages of detrital zircons for here investigated Tianli Schists, Liuyuan and Wengjialing sandstone constrain the maximum depositional ages for the respective sedimentary protoliths. Considerable time lag between onset of sedimentation and the age of source rocks suggests that the sedimentary protolith of the Tianli Schists received detritus from a wide range of cratonic sources in a tectonically passive scenario, as indicated by their elevated Zr/Sc ratios. Extraneous source for the 2700–2600 Ma detritus indicates that the sedimentary protolith for the Tianli Schists itself was deposited in a basin that received detritus from the Yangtze Block during the fragmentation of the Columbia/Nuna supercontinent. On the other hand, profuse syn-sedimentary magmatic (804–849 Ma) detritus for the Liuyuan sandstone indicates a continental arc setting, also supported by the La-Th-Sc and Th-Co-Zr signatures. The Wengjialing Formation and its equivalents were deposited in a continental rift basin, coeval with the breakup of Rodinia supercontinent, with addition of newly formed arc-related rocks (≥820 Ma) and syn-rifting magmatic rocks (810–760 Ma) as the predominant sources. These features provide substantial evidence for the paleogoegraphic reconstructions of the southeastern Yangtze Block within the Proterozoic supercontinent configurations.
... It is composed of sandstone, siltstone, slate, shale, dolostone, and minor tuffaceous volcanic rocks with a total thickness of about 20 km (Li et al., 1984), and experienced greenschist facies metamorphism. The Kunyang Group is considered to have deposited in a foreland basin setting (Ji et al., 2016;Li et al., 2013;Pang et al., 2015;Sun et al., 2009;Zhao et al., 2010). The overlying sedimentary strata are composed of Neoproterozoic to the middle Triassic submarine carbonate and clastic sedimentary sequences in a passive continental margin, and the late Triassic to Cenozoic terrigenous sedimentary sequences. ...
The Huize Zn-Pb deposit in SW China is a large Mississippi Valley-type (MVT) deposit containing more than 7 Mt Pb and Zn reserves at an ore grade of ∼25-35% Pb+Zn, and it also contains economically important resources of Ag, Cd, In, Ge and Ga. To provide better constraints on the major source of the ore metals in the deposit in situ Pb isotope composition analyses were carried out by using femtosecond laser-ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). The results indicate that the galena grains overall have restricted Pb isotopic compositions with ²⁰⁶Pb/²⁰⁴Pb of 18.486-18.526, ²⁰⁷Pb/²⁰⁴Pb of 15.738-15.806, and ²⁰⁸Pb/²⁰⁴Pb of 38.914-39.076, which are distinctively different from those for the host dolostones and Permian Emeishan flood basalts. However, the clastic sequence composed of sandstone, siltstone and slate of Proterozoic Kunyang Group has ²⁰⁶Pb/²⁰⁴Pb of 18.789-23.274, ²⁰⁷Pb/²⁰⁴Pb of 15.712-16.005, and ²⁰⁸Pb/²⁰⁴Pb of 38.169-38.933, slightly radiogenic than that for galena. It is thus likely that the clastic sequence of the Proterozoic Kunyang Group is the source of ore metals in the Huize deposit. Leaching experimental results indicate that Pb and Zn in the clastic rocks are easily accessible, and the leaching by 10% HCl resulted in the preferential release of common Pb in leachates which have ²⁰⁶Pb/²⁰⁴Pb of 18.305-18.785, ²⁰⁷Pb/²⁰⁴Pb of 15.629-15.714, and ²⁰⁸Pb/²⁰⁴Pb of 37.695-38.593, similar to the ratios for galena. The thick clastic sequence of Proterozoic Kunyang Group is therefore the predominant source of ore metals in the Huize deposit. Precipitation of sulfides from ore-forming fluids resulted from secular interaction of deep-circulated fluid and the Kunyang Group in a relatively short ore-forming process may be the major reason for the nearly constant Pb isotope signatures of the Huize Zn-Pb deposit and insignificant contribution of the host rocks.
... In the southwestern portion of the Yangtze Block, low-grade volcanic and sedimentary rocks include the Dahongshan, Dongchuan and Hekou groups (Fig. 2). Tuffs within these units have yielded U-Pb zircon ages in the range 1740-1503 Ma (Greentree and Li, 2008;Sun et al., 2009b;Zhao et al., 2010). These units are in fault contact with the ca. ...
The history of the South China Craton and the constituent Yangtze and Cathaysia blocks are directly linked to Earth's Phanerozoic and Precambrian record of supercontinent assembly and dispersal. Exposed Archean rocks are limited to isolated fragments in the Yangtze Block that preserve a record of Meso- to Neo-Archean magmatism, sedimentation and metamorphism associated with a period of global craton formation and stabilization that corresponds with the assembly of the Kenor supercontinent/supercraton. However, there are insufficient data to link its history with other similar aged cratons. The tectonostratigraphic record in South China in the Paleoproterozoic, corresponding with the assembly of Nuna, suggests that rock units in the Yangtze Block were spatially linked with northwestern Laurentia and possibly Siberia, whereas Cathaysia was joined to northern India. During the formation of Rodinia at the end of the Mesoproterozoic through to that of Pangea in the mid-Paleozoic, Cathaysia remained joined to northern India. Early Neoproterozoic supra-subduction zone magmatic arc-back arc assemblages ranging in age from ~ 1000 Ma to 810 Ma occur within Cathaysia, along its northwestern margin, and along the southeastern margin of the Yangtze Block. These rocks provide a record of convergent plate interaction, which continued along the western margin of the Yangtze Block until around 700 Ma and correlates with similar along strike subduction zone magmatism in northwest India, Seychelles and Madagascar. During the final assembly of Gondwana in the early Paleozoic suturing of India-South China with the Western Australia-Mawson blocks along the Kuunga Orogen resulted in the accretion of the Sanya Block of Hainan Island with the rest of Cathaysia. The accretion of Laurussia to Gondwana in the mid-Paleozoic to form Pangea corresponds with the initiation of lithospheric extension along the northern margin of Gondwana and the separation of a number of continental blocks, including South China, which then drifted northward across the Paleo-Tethys to collide with the Asian segment of Pangea in the Permo-Triassic.
... Detrital zircons from the Lower Kunyang Group yielded the youngest age of c. 1.78 Ga, and a tuff sample from the same group has a U-Pb zircon age of 1742 ± 13 Ma (Zhao et al. 2010). Sun et al. (2009) recently reported a SHRIMP zircon age of 1503 ± 17 Ma for a tuff sample from the E'touchang Formation in the Lower Kunyang Group. Thus, the Lower Kunyang Group likely formed between c. 1.7 Ga and c. 1.5 Ga. ...
The late Palaeoproterozoic to early Mesoproterozoic igneous rocks of southwestern China are characterized by a number of mafic intrusions and dykes. However, the origin and tectonic implications of these mafic intrusions and dykes remain unclear. The Hekou mafic intrusion, intruding into the Hekou Group in the Hekou area, SW China, is the biggest and most representative one. The intrusion is mainly composed of coarse-grained in the central zone (CZ) and medium- to fine-grained gabbroic rocks in the outer zone (OZ). Cameca secondary ion mass spectroscopy (SIMS) U–Pb zircon ages, and geochemical and Nd isotopic results for the intrusion are reported in this paper. SIMS U–Pb zircon ages indicate that the gabbroic rocks from the CZ and OZ were emplaced at 1735±6.5 Ma and 1736±4.0 Ma, respectively. This suggests that the Hekou intrusion originated from
c
. 1.7 Ga mafic magmatism in the southwestern Yangtze Block. The coarse-grained rocks in the CZ of the intrusion show fairly homogeneous major- and trace-element compositions. In contrast, the medium- to fine-grained rocks from the OZ display slightly evolved compositions, with relatively lower Mg nos, MgO, Al
2
O
3
, Cr and Ni contents, and higher SiO
2
, CaO and Zr concentrations than those of the rocks from the CZ. Although the gabbroic rocks of the intrusion have low total rare earth element (REE) contents (REE = 29.3–40.2 ppm) with slightly light REE (LREE)-enriched and heavy REE (HREE)-depleted patterns, they exhibit distinct trace-element and Nd isotopic features. The rocks from the CZ are characterized by slightly LREE-enriched and ‘convex upwards’ incompatible trace-element patterns with significant Th depletion and insignificant Nb and Ta depletion relative to La. However, the rocks from the OZ have relatively flatter REE patterns than those of the rocks from the CZ. In addition, the rocks from the OZ are slightly enriched in Th and depleted in Nb and Ta relative to La. The ε
Nd
(T) values of the CZ and the OZ rocks are +0.70 to +2.3 and −0.30 to +0.24, respectively. The parental magma for the Hekou gabbroic intrusion exhibits affinity with a subalkaline basaltic magma, which was possibly generated by relatively high degrees of partial melting of a slightly depleted asthenospheric mantle source. Their geochemical and isotopic variations were due to slight crystal fractionation with varying degrees of crustal contamination. The Hekou intrusion was therefore supposed to form in an anorogenic extensional environment. It is further suggested that
c
. 1.7 Ga is an important onset timing of widespread anorogenic magmatism in the southwestern Yangtze Block. We interpret the late Palaeoproterozoic gabbroic intrusion to represent anorogenic mafic magmatism, which was most likely related to the break-up of the Columbia supercontinent.
The Hongnipo deposit, a newly discovered large copper deposit in the Kangdian Fe-Cu metallogenic belt of southwest China, is hosted in the Paleoproterozoic metavolcanic and metasedimentary rocks of the Hekou group. The deposit comprises five strata-bound ore bodies and is associated with sporadically distributed gabbroic intrusions. Four stages of mineralization and alteration have been identified: sodic alteration (I), banded sulfide (II), magnetite (III), and sulfide vein/stockwork (IV). Extensive sodic alteration of stage I is confirmed by the composition of feldspars. Trace element analysis of magnetite suggests a formation temperature of 400 ± 50 °C and has a characteristic of IOCG deposits, while high δ¹⁸O values (8.3–11.0‰) of fluids from stage III indicate a magmatic water origin. Sulfide δ³⁴SVCDT values from stages II and IV range from −2.6 to 10.9‰ and −1.5 to 9.9‰, respectively, suggesting a mixed sulfur source from magmatic H2S and reduced seawater sulfate. Chalcopyrite from Hongnipo shows a narrow δ⁶⁵Cu range of −0.135 to 0.587‰, indicating formation at high temperatures. The lack of correlation between δ⁶⁵Cu and δ³⁴SVCDT values suggests distinct geochemical behaviors in mineralization. In summary, the Hongnipo deposit is classified as a Cu-rich section of a typical IOCG deposit.
The Sukhothai Terrane in northern Thailand comprises a continental basement and a Permo-Triassic magmatic arc related to the subduction of the main Paleo-Tethys Ocean. The Donchai Group represents the oldest sedimentary sequence of the Sukhothai Terrane and consists mainly of meta-sandstone, quartzo-feldspathic schist, phyllite and silty slate. This paper presents new detrital zircon U–Pb geochronology and Lu–Hf isotope data, and geochemical results for the sedimentary rocks of the Donchai Group to elucidate the depositional age, provenance and nature of the group. The youngest detrital zircon ages (433–403 Ma) suggest that the Donchai Group was accumulated between 433 Ma and 368 Ma, revealing Silurian–Devonian arc magmatic rocks on the western margin of the Sukhothai Terrane. Sediments of the Donchai Group were sourced from both the continental basement and a Silurian–Early Devonian magmatic arc, suggesting a depositional setting on the continental slope of a back-arc basin along the western flank of the Sukhothai Terrane. The Silurian–Devonian arc belt in SW China likely extend to the Chiang Rai region, to the west of the Sukhothai Terrane, northern Thailand, revealing the northward subduction of the Proto-Tethys Ocean along the western Simao and Sukhothai margin during the middle Paleozoic. The inferred arc and back-arc configuration of the Proto-Tethys in northern Thailand is comparable with that recently established in Yunnan, SW China.
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6858373
Zircon oxygen isotope ratios have been used to trace the incorporation of sedimentary rocks into magmas. The dramatic increase in maximum zircon δ¹⁸O values in the Paleoproterozoic observed in global databases coincides with changes in surface environments (e.g., the rise of subaerial and oxidative weathering), implying a connection between elevated zircon δ¹⁸O and these changes. Zircon δ¹⁸O between 2.5 and 2.2 Ga, however, is relatively under-constrained owing to limited available data in this age range. To augment data from this critical time period and understand potential causes for the elevated zircon δ¹⁸O values, we report U-Pb zircon ages and δ¹⁸O values of zircon, as well as, whole-rock major and trace element geochemistry of Paleoproterozoic strongly peraluminous granites (SPGs) from the southwestern margin of the Yangtze Block (China). Our geochronological data demonstrate that these SPGs crystallized at ∼2.35 Ga and that inherited zircon with ages of 2428–2721 Ma are present in these granites, indicating the source rocks of these granites were deposited, subsequently metamorphosed, and partially melted between 2.43 and 2.35 Ga. Synmagmatic zircon from samples dated in this study have εHf(t) values of −6.4 to −0.9 and high δ¹⁸O values of 7.6–9.9‰, elevated above the maximum value observed in Archean zircon (∼7‰). These granites can be divided into two groups based on whole-rock geochemistry. Both Group 1 and Group 2 granites were derived from a similar high δ¹⁸O, metapelitic source, but were generated by dehydration melting and hydrous melting, respectively. Our results demonstrate that the fine-grained sedimentary rocks from which the SPGs were derived had relatively high δ¹⁸O (as compared to older sedimentary rocks) by 2.43–2.35 Ga. The depositional time interval of the high-δ¹⁸O sedimentary sources for SPGs studied here coincides with the emergence of continental crust above sea level and the Great Oxidation Event. Supporting the findings of previous studies, the contemporaneity of our dataset with these changes in Earth’s surface environments suggests that subaerial and potentially oxidative weathering contributed (at least partially) to the elevation of δ¹⁸O of fine-grained sedimentary rocks. Recycling of these high-δ¹⁸O sedimentary rocks into magmas contributed to the dramatic change in δ¹⁸O of magmatic zircon in the earliest Paleoproterozoic. In addition, although this study is focused on a single locality, our results suggest that the abrupt shift observed in global zircon δ¹⁸O data sets likely occurred by 2.35 Ga. Last, a literature compilation of zircon δ¹⁸O data from SPGs suggested that zircon δ¹⁸O values may have also experienced a stepwise increase in the Neoproterozoic to Phanerozoic from 12 to 14‰. The coincidence of these increases in zircon δ¹⁸O values with global oxygenation events suggests that atmospheric oxygenation may have contributed to the increase in δ¹⁸O of sedimentary rocks.
Paleoproterozoic rocks are rare and essential for understanding the early evolution of the Yangtze Block. We present the newly defined Early Paleoproterozoic gneisses from the Yuanmou Complex at the western boundary of the Yangtze Block by a combined study of the structure, petrology, U-Pb age and Hf isotopic composition of zircons, and whole-rock geochemistry. The magmatic origin of inherited and detrital zircons, underlined by high Th/U ratios, of an orthogneiss and a paragneiss yield four main cluster ages of ca. 2500–2300, 2200–1770, 1580–1200, and 1100–1000 Ma. Zircon rims yield two main age groups, 970–840 and 780–750 Ma, which document the timing of overprinting metamorphic/partial melting events. Geochemical data of the orthogneiss show S-type granite characteristics. The Neoarchean to Early Paleoproterozoic ages (2500–2300 Ma) have positive εHf(t) values and two-stage model (TDM2) ages of 2760–2688 Ma, indicating a magmatic source from the depleted mantle with no crustal material involved. The Early to Middle Paleoproterozoic (2200–1770 Ma) zircon cores of mainly negative εHf(t) values and corresponding TDM2 ages (2800–2400 Ma) indicate magmatic materials predominantly from ancient (Neoarchean) crustal material with a small amount of depleted mantle material. The Early to Middle Mesoproterozoic (1580–1200 Ma) zircons indicate a magma originating from ancient crust, with minor input of mantle-derived material. The εHf(t) values of zircon rims indicate reworking of ancient crust based on the Neoproterozoic geological events (two major age groups of ca. 970–840 and 780–750 Ma), which were associated with the post-collision and partial melting events. The 2500–2300 Ma age group corresponds to the Neoarchean magmatism underneath the southwestern Yangtze Block, and the 2200–1770 Ma age group corresponds to the assembly of the Columbia supercontinent with related continental collision. The wide range of zircon cores with the Lu-Hf isotopic data provide strong evidence regarding the assembly and breakup of different stages of the supercontinent, as well as critical information on the evolution of the Yangtze Block in South China.
China has three major Precambrian cratons, named the north China craton (NCC), the south China craton (SCC), and the Tarim craton. Each craton has some billion years of geological history. The authors of this chapter favor an NCC-N Australia connection for the interval between ~1.80 and ~1.32 Ga in the supercontinent Nuna/Columbia and an NCC-NW Laurentia connection between ~1.11 and 0.78 Ga in Rodinia, based on comprehensive analyses of geological and paleomagnetic data. High-quality paleomagnetic data indicate that the SCC had experienced a long journey from the north polar regions to the Equator between ~0.8 Ga and the early Cambrian and it was unlikely once located between Australian cratons and Laurentia in the center of Rodinia in that period. The SCC’s apparent polar wander path may contain a component of true polar wander that needs more precise age constraints. Two possible paleogeographic models, either by placing the Tarim craton against NW Australia or placing it in the center of Rodinia to be the link between Laurentia and the Australia-Mawson craton, were reviewed.
Paleoproterozoic and Archean rocks in the poorly exposed Yangtze Craton provide a unique proxy for understanding early cratonic evolution. In this study, we report the newly discovered Paleoproterozoic granitoids, mafic dikes, and metasedimentary rocks in the Susong area near the northern margin of the Yangtze Craton. The zircon U–Pb analysis results of the Luohanjian granite (hereinafter referred to as LHJ-granite) and mafic dikes yielded ²⁰⁷Pb/²⁰⁶Pb ages of 2020–2002 Ma and 1837 ± 21 Ma, respectively. Metasedimentary strata that were intruded by the mafic dikes yielded detrital zircon ²⁰⁷Pb/²⁰⁶Pb ages of 2.55–2.32 Ga and 2.15–1.93 Ga, suggesting a depositional age of ∼ 1.90–1.85 Ga for the metasedimentary rock. The whole-rock εNd(t) and zircon εHf(t) values of the LHJ-granite were negative and ranged from − 10.4 to − 9.4 and − 11.4 to − 9.0, with corresponding TDM2 model ages of 3.3–3.2 Ga and ∼ 3.1 Ga, respectively. This implies that the granitic magma originated from the reworking of ancient pre-existing crustal components. The granitoids were weakly peraluminous (A/CNK = 1.00–1.18) with high SiO2 concentrations of 71.98–76.00 wt%, LREE enrichment, high (La/Yb)N values of 26.55–100.49, and moderately negative Eu anomalies, characterized by the enrichment of Rb, Ba, Th, U, and Nd, and the relative depletion of Nb, Ta, Sr, P, and Ti. These granite samples exhibited a negative correlation between SiO2 and P2O5 and low Rb/Ba (0.15–0.33) and Rb/Sr (0.30–1.55) ratios. All these features indicate that the LHJ-granite is most likely belongs to I-type granite, which may have formed via the reworking of the TTG gneiss during subduction–collisional events. In combination with the mafic dikes and metasedimentary strata, our study proposes a mid–late Paleoproterozoic geological transition from a compressional to an extensional setting, indicating a tectonic shift from a collision orogeny (2.0 Ga) to a post-collision extensional environment (1.84 Ga) in the Susong region.
This paper presents some data of the Jiaopingdu gabbro and Caiyuanzi granite at the southwestern margin of the Yangtze Block, on the geochemical compositions, zircon LA–ICP–MS U–Pb ages and Hf isotopic data. The Jiaopingdu gabbro gives the age of 1721 ± 5 Ma, the Caiyuanzi granite 1732 ± 6 Ma and 1735 ± 4 Ma, and the Wenjiacun porphyry granite 1713 ± 4 Ma, suggesting nearly contemporaneous formation time of the gabbro and granite. The bimodal feature is demonstrated by the gabbro SiO2 content of 44.64–46.87 wt% and granite 73.81–77.03 wt%. In addition, the granite has high content of SiO2 and Na2O + K2O, low content of Al2O3 and CaO, enriched in REEs (except Eu) and Zr, Nb, Ga and Y, depleted in Sr, implying it belongs to A‐type granite geochemistry and origin of within‐plate environment. The zircon ∊Hf(t) of the granite and gabbro is at the range of 2–6, which is near the 2.0 Ga evolution line of the crust, implying the parent magma of the gabbro being derived from the depleted mantle and a small amount of crustal material, and the parent magma of the granite from partial melting of the juvenile crust and some ancient crustal material at the same time. Compared with 1.8–1.7 Ga magmatism during breakup of other cratons in the world, we can deduce that the Columbia has initially broken since ca. 1.8 Ga, and some continental marginal or intra‐continental rifts occurred at ca. 1.73 Ga.
A systematic Sm-Nd isotopic study is reported for Paleoproterozoic to Late Paleozoic strata from the Dongchuan area in the southwestern Yangtze Block. The results, combined with the available detrital zircon U-Pb ages and Hf isotope data, constrain the provenances of these sedimentary rocks and further identify three important tectono-magmatic activities. Most of the Paleo-Mesoproterozoic samples (Dongchuan Group) display a wide TDM2 range of 1.92–2.52 Ga with corresponding εNd(t) values of +4.0 to −3.5, suggesting Paleoproterozoic-dominated provenances mixed with mantle-derived materials. This corresponds to the ~1.7–1.5 Ga mafic magmatic activities commonly occurred in the southwestern Yangtze Block, which are related to the early breakup of the Columbia supercontinent. The obvious vale of TDM2 and apex of εNd(t) occurred in the Neoproterozoic strata (~0.8 Ga) of the southwestern margin over the whole Yangtze Block. This is consistent with the widely recognized mantle-derived magmatism around the Yangtze Block related to the breakup of Rodinia. However, the decreases in Nd model ages are different among various regions, indicating that the Neoproterozoic mantle inputs are more profound in the southwestern and central Yangtze Block than the southeastern Yangtze and the Jiangnan orogenic belt. The late Ediacaran to early Cambrian strata from the southwestern Yangtze exhibit a decrease in TDM2 (from 2.00 to 1.67 Ga) and increase in εNd(t) (from −9.0 to −5.2). This is in accordance with the coeval juvenile crustal materials discovered in the northwestern Yangtze, which were probably derived from the assembly of the Gondwana continent. Thus, a Gondwanan affinity is suggested for the southwestern Yangtze Block. Overall, the Nd isotopic studies of the Paleoproterozoic to Late Paleozoic sedimentary strata from the southwestern Yangtze Block identified three major episodes of magmatic activities, late Paleoproterozoic (~1.7 Ga), Neoproterozoic (~0.8 Ga) and late Neoproterozoic-early Cambrian (~0.55 Ga) in the context of Columbia, Rodinia and the subsequent Gondwana supercontinents.
The Early Precambrian magmatism in the Archean–Palaeoproterozoic basement Yudongzi Complex is critical for understanding the early crustal formation and evolutionary history of the Yangtze Block in the South China Craton. In this paper, combined zircon UPb geochronological, zircon Hf isotopic, and whole‐rock geochemical studies are carried out on the granitoid gneisses from the Yudongzi Complex, north‐western Yangtze Block. The magmatic zircons from the granitoid gneiss yield a UPb upper intercept age of 2,477±18 Ma, interpreted as the crystallization age of the granitoid gneiss. The granitoid gneiss samples are characterized by high Al2O3 contents, moderate to high Sr/Y, (La/Yb)N and Na2O/K2O ratios, no obvious Eu and Sr anomalies, and depleted Nb, Ta, and Ti values that are similar to those of Archean trondhjemite–tonalite–granodiorite (TTG) suites, indicating that the investigated rocks belonging to TTG‐series rocks. They display pronounced enriched‐LREE patterns with high La/Yb values and relatively high Zr/Sm and Eu/Eu* but low Nb/Ta and Dy/Yb ratios, implying that these rocks were formed by partial melting within amphibolite‐facies conditions with mainly residual amphibole, garnet, and accessory rutile in the magma source. These rocks also display apparently low MgO, Mg#, Ni, and Cr contents, suggesting derivation from partial melting of thickened ancient lower crust. Zircon εHf(t) values from the granitoid gneiss sample vary from −10.1 to −6.9 with TDM2 of ca. 3.59–3.40 Ga, what demonstrates their crustal source nature as well. Thus, taking all these factors together, we propose that the ca. 2.48 Ga granitoid gneisses in the Yudongzi Complex might have been produced by partial melting of ancient crust material under amphibolite‐facies conditions, with primarily residual assemblages of amphibole, garnet, and attached rutile. Taking together our new data and such from previous studies, the Yangtze Block has been probably involved into a significant reworking of ancient crust event during the Early Palaeoproterozoic time.
The Paleoproterozoic era was an interval of major changes in Earth, whereas the Mesoproterozoic era comprised the “boring billion” due to the paucity of changes, especially in life forms, from 1.7 to 0.75 Ga. By the end of the Paleoproterozoic era, most of the continents were adjoined to form the Columbia or Nuna supercontinent. A series of Statherian to Calymmian rift, intracratonic, and passive margin basins developed in the Columbia recording the major accretionary and extensional events with dominant older ages rather stratigraphic depositional ages. These basins are dominated by siliciclastic successions with high abundance of red bed sandstones, but subordinate carbonate sequences are also preserved. The Paleoproterozoic‐Mesoproterozoic transition is recognized in carbonate successions of Australia, China, India, and Laurentia, which are characterized by negative δ13C values (down to −6‰) and slightly δ34 Sulfate positive anomalies (up to 30‰) close to the boundary (1650–1600 Ma). Between 1600 and 1400 Ma, carbonate platforms in these basins exhibit relatively uniform 87Sr/86Sr values around 0.705, low concentration of V and Mo, very regular and flat carbon isotope signature (mostly δ13C equals 0 ± 2‰), and the first occurrence of complex organisms (eukaryotes), suggesting low organic productivity and stable paleoclimate in these periods.
The Yinachang Fe-Cu-Au-U-REE deposit is located in the Kangdian region at the southwestern margin of the Yangtze Block. This contribution presents petrological, geochronological, whole rock geochemical, and Rare Earth Elements (REE) geochemistry of zircons of gabbro and diorite dykes associated with the Yinachang Fe-Cu-Au-U-REE deposit, aiming to constrain the age of the mineralisation and help refine our understanding of the tectonic setting of the region. Zircons from diorite have a Palaeoproterozoic U-Pb age of 2014 ± 30 Ma, and zircons from the gabbro could not be dated because they are metamict, having a high concentration of uranium. The ca. 2014 Ma age of the zircons in the diorite indicates that the southwestern part of the Yangtze Block is partly synchronous with the Columbia Supercontinent. Geochemically, the diorite and gabbro are enriched in large-ion lithophile elements (LILEs) such as Rb and U, and depleted in high-field-strength elements (HFSEs) such as Nb, P, Ti, Ba, and Sr. The diorite is enriched in light REEs (LREEs) and has a slight to negligible Eu anomaly, which are characteristic of ocean-island basalts containing mantle-derived high potassic calc-alkaline rocks. In contrast, the gabbro is weakly enriched in LREEs and has a slightly negative Eu anomaly similar to those of potassic calc-alkaline enriched mid-ocean-ridge basalt. The average combined REE content of zircons from the gabbro is 19401 ppm and is significantly higher than that of the zircons from the diorite averaging 1020 ppm. This indicates that the gabbro is closely related with the REE mineralisation at the deposit. The geochemistry of the diorite indicates that it formed at the continental margin of a volcanic-arc. It also indicates that the magmatic rocks in the region have a possible mantle plume origin contaminated by crustal material and located at a transitional zone between a rift and an ocean-continent tectonic setting.
The Neoproterozoic amalgamation and timing of collision between the Yangtze and Cathaysia sub-blocks along the Jiangnan Orogen in South China remain disputed. With a view to constrain the crustal evolution in this major orogen, here we present new results from petrology, geochemistry, zircon U-Pb chronology and Lu-Hf isotopes, on a suite of meta-sedimentary rocks from the Shuangqiaoshan Group and tuffaceous rock from the Liantuo Formation in the Jiuling terrane of central Jiangnan Orogen. Magmatic zircon grains in meta-sedimentary and sedimentary samples from the bottom to top part of the lower and upper Shuangqiaoshan groups constraints the deposition during 863–820 Ma and 797–780 Ma, respectively. The unconformities were formed during 820–797 Ma, reflecting the final amalgamation of Yangtze with Cathaysia sub-blocks along the central Jiangnan Orogen. Our data also identify four major events at 1000–800, 1500–1900, 1900–2200, 2300–2600 Ma. The Neoproterozoic detrital zircons in the lower Shuangqiaoshan Group possess variable εHf(t) values of −44.0 to +13.4. Combined with the geochemical features, these data suggest that the lower Shuangqiaoshan Group was deposited in a back-arc basin with a mixed provenance of granitic and felsic volcanic components, whereas the upper Shuangqiaoshan Group was formed in a rift basin with more granitic or felsic components in the source region. Integrating the results presented in this study with those from previous works, a five-stage crustal evolution model is proposed for the Neoproterozoic Jiangnan Orogen involving (1) intra-oceanic subduction beneath the Huaiyu oceanic island arc (1000–880 Ma), (2) collision between Huaiyu arc and Yangtze Sub-block (880–860 Ma), (3) back-arc extension beneath the Yangtze Sub-block (860–830 Ma), (4) collision between Cathaysia and Yangtze sub-blocks (830–800) and (5) intracontinental rifting throughout South China Block (800–750 Ma).
Zircon U–Pb dating and Hf isotopic analyses are performed on clastic rocks, sedimentary tuff of the Dongchuan Group (DCG), and a diabase, which is an intrusive body from the base of DCG in the SW Yangtze Block. The results provide new constraints on the Precambrian basement and the Late Paleoproterozoic to Mesoproterozoic tectonic evolution of the SW Yangtze Block, South China. DCG has been divided into four formations from the bottom to the top: Yinmin, Luoxue, Heishan, and Qinglongshan. The Yinmin Formation, which represents the oldest rock unit of DCG, was intruded by a diabase dyke. The oldest zircon age of the clastic rocks from the Yinmin Formation is 3654 Ma, with εHf(t) of −3.1 and a two-stage modeled age of 4081 Ma. Another zircon exhibits an age of 2406 Ma, with εHf(t) of −20.1 and a two-stage modeled age of 4152 Ma. These data provide indirect evidence for the residues of the Hadean crustal nuclei in the Yangtze Block. In combination with the published data, the ages of detrital zircons from the Yinmin Formation yielded three peak ages: 1.84, 2.30 and 2.71 Ga. The peaks of 1.84 and 2.71 Ga are global in distribution, and they are best correlated to the collisional accretion of cratons in North America. Moreover, the peak of 1.84 Ga coincides with the convergence of the global Columbia supercontinent. The youngest age of the detrital zircon from the Yinmin Formation was 1710 Ma; the age of the intrusive diabase was 1689 ± 34 Ma, whereas the weighted average age of the sedimentary tuff from the Heishan Formation was 1414 ± 25 Ma. It was presumed that the depositional age for DCG was 1.71–1.41 Ga, which was in accordance with the timing of the breakup of the Columbia supercontinent. At ~1.7 Ga, the geochemical data of the diabase were characterized by E-MORB and the region developed the same period A-type granites. Thus, 1.7 Ga should represent the time of the initial breakup of the Yangtze Block. Furthermore, the Yangtze Block continues to stretch and breakup until ~1.4 Ga, which is characterized by the emergence of oceanic island, deep-sea siliceous rock and flysch, representing the final breakup. In brief, the tectonic evolution of the Yangtze Block during the Late Paleoproterozoic to Mesoproterozoic coincided with the events caused by the convergence and breakup of the Columbia supercontinent, because of which, the Yangtze Block experienced extensive magmatic activity and sedimentary basin development during this period.
Formation age, sedimentary environment and source rock characteristics of the Kunyang Group are problems of considerable controversy. In order to identify the provenance and tectonic setting of the Kunyang Group in central Yunnan, the authors analyzed the sedimentary assemblage and sedimentary facies of the Kunyang Group, and conducted LA-ICP-MS detrital zircon U-Pb dating of 3 metamorphic sandstone samples from the Kunyang Group, which yielded different youngest concordant ages for Huangcaoling Formation, Heishantou Formation and Meidang Formation, being 984.0 Ma, 945.0 Ma and 954.0 Ma respectively. Age spectrum of these detrital zircons reveals a wide age range from Archean to Neoproterozoic with prominent peak at ?1.0 Ga, ?1.35 Ga and ?1.73 Ga and the second peak at ?2.44 Ga, mainly concentrated on ?1.35 Ga and ?1.73 Ga. It is inferred that the Kunyang Group source area mainly experienced 1, 1.35 and 1.73-2.44 Ga tectonic thermal events, and the age of the Dahongshan Group in southwest Yangtze Block is about 1.7Ga. The period of tectonic thermal event in Greenvillian is from 1.0 Ga to 1.3Ga. The authors also analyzed the geochemical characteristics of 20 extremely low-grade metamorphic rocks from Kunyang Group. The result shows that source rocks of Kunyang Group are quartzose cyclic sediments, felsic rocks and some mafic rocks formed in active continental margin or continental island arc. It is concluded that, from late Mesoproterozoic to early Neoproterozoic (0.95-1.0 Ga), the Kunyang Group was formed in the foreland basin with its provenance mainly from the Dahongshan Group in southwestern Yangtze block and Grenville-aged island arc.
The Mesoproterozoic terranes are mainly distributed at the northern and western margin of the Yangtze Block and can be discerned into 2 major stages, early Pt2 (1.8–1.5 Ga) and late Pt2 (1.5–1.0 Ga), according to the formation time. The sequence of early Pt2 stage is present as the Dahongshan, Dongchuan, and Hekou Groups at the southwestern margin of the Yangtze Block, consisting of sandstone, siltstone, slate, phyllite, dolomitic marble, and marble, with volcanic intercalation in which usually produce the Fe–Cu deposits. In addition, some magmatic rocks of early Pt2 stage occur as stocks and dykes intruding the early Pt2 sequence in the area. The magmas can be subdivided into two events: the early ca 1.7 Ga dominated by dolerites and the late ca 1.5 Ga gabbro stocks and dykes. The sequence of late Pt2 stage crop out as the Kunyang, Huili Groups at the southwestern margin and the Shennongjia Group at the northern margin of the Yangtze Block. Magmatic events are obviously manifested in the period (1.1–1.0 Ga) in the block, but magmatic rocks (including the eruptives and intrusives) in different areas vary in formation setting according to their association and geochemical features. While in the Cathaysian Block and Jiangnan orogenic belt, the Mesoproterozoic terranes are only rarely exposed, such as the 1.5–1.4 Ga Baoban Group (including part of the Shilu Group) in Hainan Island of the Cathaysian Block, and the Tianli schist and Tieshajie Formation of Late Mesoproterozoic in the eastern segment of the Jiangnan belt.
The major advances in the study of Mesoproterozoic isotopic geochronology in the aspects of stratigraphy and thermo -tectonic events as well as their geological significance since the 3rd Stratigraphic Congress of China held in 2000 are described in this paper. It is pointed out that the establishment of a type stratiraphic section of the upper Mesoproterozoic and the revision of the Mesoproterozoic time scale of China are the main new key problems at present.
Late Mesoproterozoic to early Neoproterozoic igneous rocks (ca. 1100 Ma to >860 Ma) are sparse in the southwestern Yangtze Block, hindering our understanding of South China's position during the late Mesoproterozoic to early Neoproterozoic assembly of the supercontinent Rodinia. We report here Cameca secondary ion mass spectrometry (SIMS) zircon U–Pb ages, geochemistry, and Nd–Hf isotopic data for mafic dykes that intruded in the lower Tianbaoshan Formation, and that of intermediate to felsic volcanic rocks from the upper Tianbaoshan Formation of the Huili Group in southwestern Yangtze Block. The mafic dykes were formed at 1023 ± 6.7 Ma. The volcanic rocks were dated at 1025 ± 13 Ma and 1021 ± 6.4 Ma, contemporaneous to the mafic dykes. The mafic dykes show weakly positive ɛNd(t) values (+0.41 to +1.6) and positive ɛHf(t) values (+7.0 to +10.3). They are characterized by slightly LREE-enriched and HREE-depleted patterns and the trace element patterns with typical depletion of Nb and Ta and slightly enrichment of Th relative to La. The parental magma for the mafic rocks exhibits affinity of low-Ti tholeiitic basaltic magma generated by melting of a depleted asthenospheric mantle source. The primary magma of these mafic rocks likely underwent variable degrees of the fractional crystallization and crustal contamination. The intermediate to felsic volcanic rocks in the Tianbaoshan Formation are characterized by significantly LREE-enriched and slightly HREE-depleted patterns, showing negative Nb–Ta, Eu, Sr, P and Ti anomalies in the primitive mantle-normalized multi-element plot. In addition, the volcanic rocks display variably elevated Ga, Rb, Zr, REE, and Y concentrations, and high Ga/Al ratios (2.31–2.64), consistent with the geochemical characteristics of A2-type granites. The volcanic rocks exhibit negative ɛNd(t) values (−5.1 to −7.1) and variable ɛHf(t) values (−0.67 to +3.9). They give two-stage Nd model ages (TNd2DM) and two-stage Hf model ages (THf2DM) of 1.83–1.99 Ga and 1.62–1.91 Ga, respectively. The Nd–Hf isotopic signatures indicate that the primitive magma for the Tianbaoshan intermediate to felsic volcanic rocks was probably derived from partial melting of the granulite-facies lower crust driven by underplating of mafic magmas, and underwent extensive fractional crystallization during emplacement. The studied 1.02 Ga felsic volcanic rocks and mafic dykes at Huili are interpreted to have formed in an impactogen setting during the initial stage of collision between the Yangtze and Cathaysia blocks prior to the Sibao Orogeny.
The Yunkai terrane had always been considered as an important part of the Precambrian basement outcropped in southwestern South China Block (SCB), but the understanding of basement compositions has been controversial. This study presents a suite of geochemical and zircon U-Pb-Hf isotopic data of the basement metamorphic rocks in the Yunkai terrane. Analytical results show that the Yunkai basement is mainly composed of meta-sedimentary rocks deposited in Late Neoporoterozoic-Early Paleozoic. These sedimentary rocks with moderate composition maturity show high SiO2 and low Al2O3, CaO, Na2O relative to the average upper crust composition. Their trace element characteristic are similar to those of post-Archean Australian shales (PAAS), with exception of strong depletion in Sr, Cr, Ni, slightly depletion in high field-strength element (e. g. Nb, Ta) and weakly enriched in Zr, Hf, Th, U, suggesting that provenances of these sedimentary rocks have more felsic components with minor mafic components. The geochemical characteristics and detrital zircon dating results indicate that these sedimentary rocks were deposited in a passive continental margin setting and derived from both the recycled old crust and some unmodified Neoproterozoic magma material. Integrating our data with previous data, it is suggested that the basement rocks in Yunkai terrane can be divided into two groups. First group samples were formed early (<850 - 522Ma), and show affinity with those in the Nanling area. Four major magmatic events (2600 - 2350Ma, 2000 - 1750Ma, 1700 - 1500Ma and 900 - 750Ma) occurred in their source, all of which involve both the reworking of older crust and the growth of juvenile crust. The most important juvenile crust generation took place in Neoarchean and Grenvillian. Second group samples were deposited after 517Ma and have the same components as those in the southern Yangtze Block, suggesting their affinity relation. Four different episodes of magmatism (2600 - 2350Ma, 2000 - 1750Ma, 1700 - 1500Ma, 900 - 750Ma) occurred in the source of second group samples. Late Neoarchean-Early Paleoproterozoic magmatism mainly involved the reworking of older crust. Minor juvenile crust was generated in Late Paleoproterozoic-Early Mesoproterozoic, and most intense juvenile crust generation was brought about in Neoproterozoic. The change of detritus in different episodes of sedimentary rocks manifests that the Yunkai terrane basin probably suffered the influence of a tectonic event at <522Ma to 517Ma, leading to provenance variation from the Cathaysia Block to the Yangtze Block. This event probably is initial stage of Early Paleozoic orogeny in the Cathaysia. According to our data and other lines of evidence, we think that the Yunkai terrane belongs to the Cathaysia Block, and the boundary between the Yangtze Block and the Cathaysia Block is likely located between Pingle and Pingnan in the north of Yunkai terrane.
The Yinachang Fe-Cu-REE ore deposit is hosted in the Paleoproterozoic Yinachang Formation of the Lower Kunyang Group in the Kangdian iron-copper metallogenic province, SW China. The main minerals in the Yinachang ore bodies consist of chalcopyrite, magnetite, quartz and calcite. As the host rocks of the deposit had experienced intensively alternation and metamorphism, the age and origin of the Yinachang deposit are still a matter of hot debate. U-Pb ages of detrital zircons from the volcanic tuff and breccia in the Yinachang Formation have been used to identify the provenance and evaluate the age of the Yinachang Formation of the Lower Kunyang Group. Most analyzed zircon grains show oscillatory zoning and have high Th/U ratios (>0. 4), suggesting that they were mainly derived from igneous rocks. A total amounts of about 200 detrital zircons exhibit U-Pb age populations at 1. 75 ∼1. 88Ga, 1. 90 ∼2. OOGa, 2. 02 ∼2. 20Ga and 2. 30 ∼2. 40Ga, with the oldest 207Pb/ 206Pb age of ∼3. OGa and the youngest age of ca. 1750Ma. The dating results provide a maximum deposition age of ca. 1. 7Ga for the Yinachang Formation, and suggest the possible existence of older basement. Rhenium-osmium dating for six chalcopyrite samples from the Yinachang Fe-Cu-REE deposit was conducted to constrain the timing of sulfide mineralization. Direct Re-Os dating for chalcopyrite of ore minerals yields an isochron age of 1690 ±99 Ma (MSWD=9.0) and a weighted mean of 1685 ±37Ma (MSWD =3. 0), respectively, indicating the main ore-forming age of about 1. 7Ga. In addition, the major ore types exhibit significantly positive Eu anomaly and LREE enrichment, similar to those of modern submarine hydrothermal fluids. The above dating results reveal that the ore-forming age of the deposit is nearly contemporaneous with the deposition timing of the Yinachang Formation, and the characteristics of fluid deduced from REE indicate that the ore formation was related to submarine hydrothermal fluids activity. It is therefore suggested that the Yinachang Fe-Cu-REE deposit is a volcanic exhalation-hydrothermal sedimentary deposit. Several recent studies showed the occurrence of relatively widespread magmatism at ca. 1.7Ga and large numbers of synchronous Fe-Cu deposits, suggesting that the magmatism is probably the crucial factor for the formation of deposits in this region. Furthermore, the Fe-Cu deposits in the Kangdian region may be related to the breakup of the Columbia supercontinent at about 1. 7Ga.
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