The Proterozoic evolution of northern Siberian Craton margin: a comparison of U–Pb–Hf signatures from sedimentary units of the Taimyr orogenic belt and the Siberian platform

Identifying the cratonic affinity of Neoproterozoic crust that surrounds the northern margin of the Siberian Craton (SC) is critical for determining its tectonic evolution and placing the Craton in Neoproterozoic supercontinental reconstructions. Integration of new U–Pb–Hf detrital zircon data with regional geological constraints indicates that distinct Neoproterozoic arc-related magmatic belts can be identified within the Taimyr orogen. Sedimentary rocks derived from 970 to 800 Ma arc-related suites reveal abundant Archean and Paleoproterozoic detritus, characteristic of the SC. The 720–600 Ma arc-related zircon population from the younger Cambrian sedimentary rocks is also complemented by an exotic juvenile Mesoproterozoic zircon population and erosional products of older arc-related suites. Nonetheless, numerous evidences imply that both arcs broadly reworked Siberian basement components. We suggest that the early Neoproterozoic (ca. 970–800 Ma) arc system of the Taimyr orogen evolved on the active margin of the SC and probably extended along the periphery of Rodinia into Valhalla orogen of NE Laurentia. We also suggest the late Neoproterozoic (750–550 Ma) arc system could have been part of the Timanian orogen, which linked Siberia and Baltica at the Precambrian/Phanerozoic transition.     

Chronological constraints on the tectonic evolution of the Chinese Tianshan Orogen through detrital zircons from modern and palaeo-river sands

The Chinese Tianshan Orogen marks prolonged and complicated interactions between the southwestern Palaeo-Asian Ocean and surrounding blocks. New and previously published detrital zircon chronological data from modern and palaeo-river sands were compiled to reveal its tectonic evolution. It is characterized by predominant Palaeozoic as well as minor Mesozoic and Precambrian detrital zircon ages with a multimodal characteristic. The oldest Phanerozoic zircon population (peaking at 475 Ma) is a result of subduction and closure of the early Palaeozoic Terskey Ocean. However, the absence of this peak in the Chinese North and southern South Tianshan suggests that subductions of the North and South Tianshan oceans may not have initiated until the Late Ordovician with subsequent 460–390 and 360–320 Ma arc magmatism. Similar to the magmatic suite in classic collisional orogens, the youngest massive 320–270 Ma magmatism is suggested to be post-collisional. The North and South Tianshan oceans therefore probably had their closure to form the Chinese Tianshan Orogen during the late Carboniferous. The weak Mesozoic intra-plate magmatism further rejects a late Permian–Triassic Tianshan Orogen due to a lack of extensive syn- and post-collisional magmatism. Moreover, diverse Precambrian detrital zircon age patterns indicate that the surrounding blocks have distinct evolutionary processes with short-term amalgamation during the Meso- to Neoproterozoic.     

Detrital zircon U–Pb ages and whole-rock geochemistry of the Neoproterozoic Paulistana and Santa Filomena complexes,Borborema Province,northeastern Brazil: implications for source area composition,provenance, and tectonic setting

The Paulistana and Santa Filomena Complexes are situated in the southern part of the Borborema Province (northeastern Brazil), in the Riacho do Pontal Orogen, and represent meta-volcano-sedimentary sequences. We present compositional variations in the metasedimentary rocks and new U–Pb detrital zircon data. Major and trace elements indicate that the metasedimentary rocks from the Paulistana and Santa Filomena Complexes are composed mostly of immature to mature sediments derived from felsic-intermediate sources with moderate to slightly high chemical weathering. The geochemical signatures of the sediment protoliths for both complexes are characteristic of continental magmatic arc settings with minor contribution from recycled sediment sources. The source area for the Paulistana Complex rocks follow the compositional trend between calc-alkaline granites and granodiorites, whereas the Santa Filomena Complex rocks have a more restricted composition trending to more granodioritic sources. For the Paulistana Complex, two main source ages were identified: (1) Tonian (ca. 950 Ma – sample RPE-58) and Tonian–Stenian (ca. 1.0 Ga – sample RPE-103). These data coupled with geochemical information suggest that the Cariris Velhos arc system was the main source area for the Paulistana Complex. Regarding the Santa Filomena metasedimentary rocks, potential source-areas include: (1) Neoarchaean rocks (~2.6 Ga) represented by the adjacent basement rocks of the Riacho do Pontal Orogen; (2) Rhyacian–Orosirian rocks (2.2–2.0 Ga) of the Riacho do Pontal Orogen and the Pernambuco–Alagoas terrain, which include an augen-gneiss with arc-related geochemical signature; (3) Statherian granites (1.7–1.6 Ga); and (4) Cariris Velhos crust (1000–920 Ma). The metasedimentary rocks of the Paulistana Complex were deposited in a rift stage (ca. 900 Ma), which is related to the break-up of the Rodinia supercontinent. The metasedimentary rocks of the Santa Filomena Complex most probably were deposited in another rift stage (ca. 750–700 Ma) and could be correlatives of the rift formation of the Canindé Domain (Sergipano Orogen).     

Petrogenesis and geodynamic setting of the Triassic granitoid plutons in West Qinling,China: insights from LA-ICP-MS zircon U–Pb ages,Lu–Hf isotope signatures and geochemical characteristics of the Zhongchuan pluton

West Qinling is one of the most important parts of the Qinling orogenic belt and includes acidic–intermediate plutons and many types of ore deposits. In this article, we collected geochemical and geochronological data for the Triassic granitoid plutons of West Qinling and found that nearly all plutons share the similar features with the Zhongchuan pluton. We present new laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages, major and trace element geochemistry, and zircon Hf isotope systematics for the granites of the Zhongchuan pluton to elucidate the evolution of granitoid plutons in West Qinling during the Triassic. LA-ICP-MS zircon U–Pb dating indicates that the Xujiaba and Guandigou units formed at 220.1 ± 1.2 and 215.9 ± 0.85 Ma, respectively, reflecting the time of the Late Triassic. The rocks of the Zhongchuan pluton are metaluminous to weakly peraluminous and have a high-K calc-alkaline to shoshonite series with high SiO₂ (63.59–76.22%) and low P₂O₅ (0–0.2%) concentrations, a high K₂O/Na₂O ratio (1.18–17.92), a high differentiation index (78.45–93.04) and a medium A/CNK ratio (0.98–1.69). The zircon Hf isotope dating indicates that the Xujiaba and Guandigou units have an inhomogeneous ε_Hf(t) (?4.425 to 1.067 for Xujiaba and ?4.920 to 2.042 for Guandigou) and two-stage Hf model ages (1123–1531 Ma for Xujiaba and 1115–2342 Ma for Guandigou). The geochemical and isotopic data imply that the granites of each unit share the same origin. They probably derived from the partial melt of metagreywackes and then mixed with the mantle-derived magma. Based on the regional geological history, petrographic characteristics and new geochemical and isotopic data of the Zhongchuan pluton, we suggest that the Triassic magma was derived from the partial melts of metagreywackes and was influenced by the mantle-derived melt during the collision of the Yangtze and Qinling plates.     

Constraining the timing of porphyry mineralization in northwest Iran in relation to Lesser Caucasus and Central Iran; Re–Os age data for Sungun porphyry Cu–Mo deposit

The Neo-Tethyan subduction in Iran is characterized by the Urumieh–Dokhtar magmatic arc (UDMA), formed by northeast-ward subduction of the oceanic crust beneath the central Iran. This belt coincides with the porphyry copper metallogenic belt that comprises several metallogenic zones, including Ahar–Jolfa in northwest Iran. The Ahar–Jolfa metallogenic zone encompasses two main batholiths of Qaradagh and Sheyvardagh and numerous intrusive bodies of Cenozoic, which have produced many base and precious metal deposits and prospects. The former is considered as continuation of the Meghri–Ordubad pluton in South Armenian Block (SAB), which also hosts porphyry copper deposits (PCDs). The Sungun PCD is the largest occurrence in northwest Iran. Rhenium-Osmium ages of Sungun molybdenites are early Miocene and range between 22.9 ± 0.2 and 21.7 ± 0.2 Ma. Comparison of the ages obtained here with published ages for mineralization across the region suggests the following sequence. The earliest porphyry Cu–Mo mineralization event in northwest Iran is represented by Saheb Divan PCD of late Eocene age, which is followed by the second epoch of middle Oligocene, including the Cu–Mo–Au mineralization at Qarachilar and the Haftcheshmeh PCD. Mineralization in Sungun, Masjed Daghi, Kighal and Niaz deposits corresponds to the third mineralization event in northwest Iran. The first epoch in northwest Iran postdates all Eocene mineralizations in SAB, while the second epoch is coeval with Paragachay and the first-stage of Kadjaran PCDs. Its third epoch is younger than all mineralizations in SAB, except the second stage in Kadjaran PCD. Finally, the Cu mineralization epochs in northwest Iran are older than nearly all PCDs and prospects in Central Iran (except the Bondar Hanza PCD), altogether revealing an old to young trend along the UDMA and the porphyry Cu belt towards southeast, resulted from diachronous, later closure of the Neo-Tethyan oceanic basin in central and SE Iran.     

Subduction-related 200 Ma Talun metagranite,SE Taiwan: an age constraint for palaeo-Pacific plate subduction beneath South China Block during the Mesozoic

Various tectonic models have been proposed to account for the widely distributed igneous activities in the southeastern part of the South China Block (SCB) during the Triassic–Jurassic period. One of the major contending debates is on the timing of initiation of the palaeo-Pacific plate subduction under the SCB, due to lack of unequivocal evidence for arc magmatism during the period in this region.

The 191 ± 10 Ma (N = 5, MSWD = 12) calc-alkalic high-K I-type Talun metagranite occurs in the southern Tailuko belt of the Tananao metamorphic complex, Taiwan. In terms of age, this metagranite belongs to the Early Yanshanian igneous activity in the southeastern part of the SCB. However, its geographic position does not accord with the well-known general oceanward younging trend of the Yansnanian igneous rocks. In view of the large age uncertainty reported, this metagranite is redated in this study. Some zircons of this metagranite are high in U content and are metamict. Zircons with low U contents are analysed by SHRIMP yielding a more precise age of 200 ± 2 Ma (N = 10, MSWD = 4). In particular, the εHf(t) of these dated zircons ranges from +4.5 to +12.9. The metagranite mainly consists of quartz, K-feldspar, plagioclase, with minor amounts of garnet, biotite, zircon, apatite, and pyrrhotite. Chlorite and calcite are secondary phases overprinted by the later tectonic event(s). Its initial Sr isotope compositional range is 0.70473–0.70588, and εNd(t), +2.4 to +3.6. The results demonstrate that the genesis of this metagranite could be attributed to the assimilation-fractionation of a depleted mantle-derived basaltic magma, which was most likely related to arc magmatism. The present study therefore offers key evidence that during the Mesozoic, the palaeo-Pacific plate subduction underneath the SCB would have taken place no later than the very early Jurassic.     

新疆北部青河县阿斯喀尔特铍矿区花岗质岩石年代学及地球化学特征

新疆北部青河县阿斯喀尔特铍矿床的形成与岩浆活动密切相关,是中国花岗岩型铍矿床的典型代表。对矿区斑状二云母二长花岗岩进行LA-ICP-MS锆石U-Pb年龄测试,获得其加权平均年龄为(216.7±2.8)Ma(MSWD=0.48),表明该岩体形成时代为晚三叠世,据此限定阿斯喀尔特铍矿床成矿时代略晚于216 Ma,为晚三叠世—早侏罗世。岩石具有高硅(w(Si O2)=70.86%~76.34%)、富碱(ALK=5.54~9.30)、富铝(w(Al_2O_3)=13.00%~14.74%,A/CNK=0.99~1.23)、低钛(w(Ti O2)=0.02%~0.18%)和镁(w(Mg O)=0.02%~1.21%)特征,为过铝质中钾-高钾岩石系列。稀土元素配分型式显示LREE的相对弱富集,HREE较平坦以及Eu弱-中等的负异常(δEu=0.37~0.90),呈略右倾型。微量元素Ba、Sr、Hf、Ti等具负异常,Rb、Th、K、Nb、Ta、La、Ce、Nd、Sm等具正异常,Rb/Sr比值较高(9.34~26.81),显示出S型花岗岩特征。结合区域资料,认为阿斯喀尔特铍矿矿区印支期花岗岩形成于后造山构造阶段,可能是上地壳含砂泥质岩石部分熔融的产物。     

江苏仑山金矿床流体包裹体、稳定同位素和成矿年代学研究

仑山金矿床位于宁镇矿集区东端。成矿期分为沉积成矿期和热液成矿期,后者可进一步划分为热液Ⅰ阶段和热液Ⅱ阶段。流体包裹体研究表明,热液Ⅰ阶段石英中的气液两相流体包裹体均一温度多集中在330~366℃之间,盐度w(Na Cl_(eq))变化于4.96%~6.74%之间,热液Ⅰ阶段方解石中气液两相流体包裹体均一温度多集中在150~240℃之间,w(Na Cl_(eq))变化于0.71%~9.80%之间,成矿流体为中高温低盐度流体;热液Ⅱ阶段石英、方解石和萤石的流体包裹体均一温度变化于124~260℃,盐度w(Na Cl_(eq))变化于1%~8%之间,成矿流体为中温低盐度流体。氢、氧同位素研究表明,热液Ⅰ阶段成矿流体为岩浆流体,热液Ⅱ阶段成矿流体以大气降水占主导,但仍有少量岩浆流体。硫同位素研究表明,仑山金矿床沉积成矿期硫除来源于三叠系青龙群膏盐层外,有机质也参与了沉积成矿期中金矿的形成。热液Ⅰ阶段硫来源于沉积成岩阶段黄铁矿的活化迁移和富集,岩浆硫也提供了成矿物质。萤石Sm-Nd测年分析表明,仑山金矿床热液Ⅱ阶段成矿年龄为(93.7±3.1)Ma,推断主成矿阶段形成于晚白垩世。仑山金矿床的形成代表着长江中下游成矿带最晚期的成矿作用。     

赣西北大雾塘钨矿区地质特征及Re-Os同位素年代学研究

通过对大湖塘钨矿田的大雾塘钨矿区辉钼矿Re-Os同位素年代学的研究,测得辉钼矿的w(Re)为0.3368×10~(-6)~8.256×10~(-6),获得的5个模式年龄比较一致,介于(136.6±2.2)Ma~(138.4±2.4)Ma,加权平均年龄为(137.7±2.7)Ma(MSWD=0.07)。将5个模式年龄进行等时线年龄计算,获得一条相关性较好的~(187)Re-~(187)Os等时线,计算得到辉钼矿Re-Os等时线年龄为(137.9±2.0)Ma(MSWD=0.20),与加权平均年龄一致,可代表辉钼矿的形成年龄。结合石门寺和狮尾洞矿区典型矿床地质、地球化学特征和成岩作用时空关系,认为大雾塘矿床的形成是大湖塘钨矿田的第二期次(140 Ma)大规模成矿作用的产物,2期成矿作用可能是大湖塘钨矿田巨量成矿元素堆积的重要原因之一。     

海南省新村钼矿床LA-ICP-MS锆石U-Pb和辉钼矿Re-Os年龄及其地质意义

新村钼矿床是海南省近年来发现的具中型规模的钼矿床。文章对赋矿二长花岗岩进行LA-ICP-MS锆石U-Pb同位素测年,获得~(206)Pb/~(238)U年龄加权平均值为(102.0±1.5)Ma(MSWD=2.3);对辉钼矿进行Re-Os同位素定年,获得5件样品的模式年龄范围为(97.29±1.43)Ma~(98.52±1.55)Ma,加权平均年龄为(97.84±0.64)Ma,等时线年龄为(98.90±3.40)Ma,成岩年龄与成矿年龄在误差范围内一致。辉钼矿的Re含量和锆石Hf同位素特征指示新村钼矿的成岩成矿物质来自于壳幔混源。新村钼矿床的成岩成矿年龄与海南岛最重要的钼成矿期(95~105 Ma)一致,属中国东部早白垩世晚期—晚白垩世早期钼成矿事件的一部分,与该时期岩石圈大规模拉伸减薄、软流圈上涌及强烈壳-幔作用密切相关。