Li Zuochen

The LA-ICP-MS zircons U-Pb ages and geochemistry of the Baihua basic igneous complexes in Tianshui area of West Qinling

Baihua meta-igneous complex consists mainly of pyroxenite-gabbro(diorite)-diorite-quartz diorite. They form a complete comagmatic evolutionary series. The geochemical characteristics of basic-intermediate basic igneous rocks indicate that they belong to a tholeiite suite. The REE distribution pattern is nearly flat type and LREE is slightly enriched type, and their primitive mantle-normalized and MORB-normalized trace element spider diagrams are generally similar; the LIL elements (LILE) Cs, Ba, Sr, Th and U are enriched, but Rb, K and the HFSEs Nb, P, Zr, Sm, Ti and Y are relatively depleted. All these show comagmatic evolution and origin characteristics. The tectonics environment discrimination of trace element reveals that these igneous complexes formed in an island-arc setting. The LA-ICP-MS single-zircons U-Pb age of Baihua basic igneous complex is 434.6±1.5 Ma (MSWD = 1.3), which proves that the formation time of the island-arc type magmatite in the northern zone of West Qinling is Late Ordovician or Early Silurian, also reveals that the timing of subduction of paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magmatic activities is probably Middle-Late Ordovician to Early Silurian.

Geochronology, Geochemistry and Tectonic Setting of the Bairiqiete Granodiorite Intrusion (Rock Mass) from the Buqingshan Tectonic Mélange Belt in the Southern Margin of East Kunlun

: This study focuses on the zircon U–Pb geochronology and geochemistry of the Bairiqiete granodiorite intrusion (rock mass) from the Buqingshan tectonic melange belt in the southern margin of East Kunlun. The results show that the zircons are characterized by internal oscillatory zoning and high Th/U (0.14–0.80), indicative of an igneous origin. LA–ICP–MS U–Pb dating of zircons from the Bairiqiete granodiorite yielded an age of 439.0 ± 1.9 Ma (MSWD = 0.34), implying that the Bairiqiete granodiorite formed in the early Silurian. Geochemical analyses show that the rocks are medium-K calc-alkaline, relatively high in Al2O3 (14.57–18.34 wt%) and metaluminous to weakly peraluminous. Rare-earth elements have low concentrations (45.49–168.31 ppm) and incline rightward with weak negative to weak positive Eu anomalies (δ5Eu = 0.64–1.34). Trace-element geochemistry is characterized by negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of Rb, Th and Ba. Moreover, the rocks have similar geochemical features with adakites. The Bairiqiete granodiorite appears to have a continental crust source and formed in a subduction-related island-arc setting. The Bairiqiete granodiorite was formed due to partial melting of the lower crust and suggests subduction in the Buqingshan area of the Proto-Tethys Ocean.

Geochemical Features, Age, and Tectonic Significance of the Kekekete Mafic‐ultramafic Rocks, East Kunlun Orogen, China

: The Kekekete mafic-ultramafic rocks are exposed in the Kekesha-Kekekete-Dawate area, which are in the eastern part of the East Kunlun Orogenic Belt It outcrops as tectonic slices intruding tectonically in the Paleoproterozoic Baishahe Group and the Paleozoic Nachitai Group. The Kekekete mafic and ultramafic rocks is located near the central fault in East Kunlun and lithologically mainly consists of serpentinite, augite peridotite, and gabbro. The LA-ICP-MS zircon U-Pb age of the gabbro is 501 ± 7 Ma, indicating that Kekekete mafic-ultramafic rocks formed in the Middle Cambrian. This rock assemblage is relatively poor in SiO2 and (Na2O+K2O) but rich in MgO and SFeO. The chondrite-normalized REE patterns of the gabbro dip slightly to the right; the primitive mantle and MORB-normalized spidergrams of trace elements show enrichment of large-ion lithophile elements (Cs, Rb, Ba, etc.) and no differentiation of high field strength elements. The general dominance of E-MORB features and the geochemical characteristics of OIB suggest that the Kekekete mafic-ultramafic rocks formed in an initial oceanic basin with slightly enriched mantle being featured by varying degrees of mixing of N-MORB depleted mantle and a similar-OIB-type source. From a comprehensive study of the previous data, the author believes that the tectonic history of the East Kunlun region was controlled by a geodynamic system of rifting and extension in the late stages of the Neoproterozoic to early stages of the Early Paleozoic and this formed the paleo-oceanic basin or rift system now represented by the ophiolites along the central fault in East Kunlun, the Kekekete mafic-ultramafic rocks and Delisitan ophiolite.

U–Pb Zircon Geochronology and Geochemistry of the Neoproterozoic Liujiaping Group Volcanics in the Northwest Margin of the Yangtze Block: Implications For the Breakup of the Rodinia Supercontinent

petrogenesis 和从 back-Longmenshan 的 Liujiaping 组的暴烈的岩石的锆石的起源的调查在扬采·布洛克的西北边缘的构造的带被 U-Pb 地球年代学和地球化学的分析进行。结果证明选择锆石被内部摆动的 zonings 和高 Th/U 比率(0.43-1.18 ) 描绘，显示火的起源。Liujiaping 组锆石标明日期的 LA-ICP-MS U-Pb 的 Geochronological 结果产出 809 ± 的年龄11 妈(MSWD = 2.2 ) ，暗示暴烈的岩石在迟了的 Neoproterozoic 被形成。岩石是计算碱的 Geochemical 分析表演，在艾尔，和 metaluminous 使过饱和到弱 peraluminous。稀土元素的元素在高集中(96.04-265.48 ppm ) 是在场的并且显示出一个向右坡度和一个中等否定的 Eu 异例，类似于大陆人裂缝流纹岩的。踪迹元素地球化学被 Nb 的明显的否定异例描绘， Ta， P， Th， Ti，内部 alia，和 K 的强壮的否定异例， Rb， Sr，等。我们断定 Liujiaping 组织暴烈的岩石源于典型大陆人外壳来源 petrogenesis 并且在一个大陆人边缘背景被形成，它没有关系到 subduction ，并且这样，由于外壳的变厚的更低的外壳的部分融化的产品在西北的扬采·布洛克由活跃大陆人边缘 subduction 和弧大陆碰撞造山运动引起了并且被 Rodinia supercontinent 的决裂在 Neoproterozoic 期间触发。

Late Cambrian SSZ-type Ophiolites in Acite Zone, East Kunlun Orogen of Northern Tibet Plateau: Insights from Zircon U-Pb Isotopes and Geochemistry of Oceanic Crust Rocks

East Kunlun orogen(EKO) stretching more than 1000 km in E-W extension is located in the western segment of Central Orogen Belt(COB), China(Xu et al., 2006, Li et al., 2014). There outcropped Cambrian ophiolites recording the tectonic evolution history of a Proto-Tethys ocean lying in the northern edge of Gondwana Continent during Early Paleozoic era(Li et al., 2013a,b). * The Acite Ophiolitic mélange is located in the eastern section of EKO, western COB. Detailed geological mapping revealed that Acite Ophiolitic mélange mainly include mantle peritotites, metabasalts, metagabbros, metabasaltic andesites and marbles(originally neritic marine limestone) (Fig. 1a,b), which are crucial for understanding the possible progressive evolution process of supra-subduction zone(SSZ) forearc magmas for Acite ophiolite.

Magma Mixing and Mingling for Xiangjiananshan Granitic batholith at eastern area of the East Kunlun Orogenic Belt

1 Key Laboratory of Western China’s Mineral Resources and Geological Engineering, Ministry of Education, Key Laboratory for the study of Focused Magmatism and Giant Ore Deposits, MLR, Faculty of Earth Science and Resources Chang’an University, Xi’an 710054, Shaanxi China 2 Nanyang Institutte of Technolog, School of Civil Engineeringy, Nanyang 473000, Henan, China 3 School of Earth Science and Resource, China University of Geosciences, Beijing 100083, China