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Qin X.,Guilin University of Technology | Qin X.,China Institute of Mineral Resources | Wang Z.,China Institute of Mineral Resources | Hu G.,Guangxi Institute of Regional Geological Survey | And 2 more authors.
Acta Petrologica Sinica | Year: 2013

The Hudong gneissic composite pluton is located in the junction of Guangdong and Guangxi provinces and is composed mainly of gneissic tonalite, granodiorite and monzonitic granite. LA-ICFMS U-Pb dating result of zircon from a gnessic granodiorite sample yields an emplacement age of 443. 1 ± 2. OMa. The gneissic tonalites and granodiorites are metaluminous ( A/CNK =0. 83 ∼ 0. 93 ) and belong to medium-K amphilx)le calc-alkaline granitoids (ACG) with relatively low SiO2 (62. 92% ∼67. 54% ) and K2O+ Na20 (3. 98% ∼5. 17% ). In contrast, the gneissic monzonitic granites are metaluminous to weakly peraluminous ( A/CNK =0. 92 ∼ 1.05) and belong to high K calc-alkaline granites ( KCG) with higher SiO 2(71.55% ∼ 72. 78% ) and K20 + Na20 ( 6.65% ∼ 7. 57% ). Rocks from the Hudong gneissic composite pluton are characterized by relative enrichment in LILEs (e. g. , U, Ba, Kb and Th) and LKEEs and pronounced depletion in HESEs (e.g. , Nb, Ta and Ti) and HKEEs, highly radiogenic Sr (87 Sr/86 Sr(i)= 0. 71268 ∼0.71482) and Pb (e. g. , 206Pb/204Pb (i)=18.17 ∼18.36), and nonradiogenic Nd (εNd(t) = - 9. 4 ∼2.6) isotopic compositions. Such geochemical features are typical of subduction-related arc magmatic rocks. In combination with the regional tectonic evolution, we consider that the Hudong gneissic composite pluton was most likely produced related to the southward subduction of the ocean floor and collision between the Yangtze and Cathaysian blocks. Asthenospheric upwelling followed by the oceanic subduction provided enough heat supply to melt both the overriding lithospheric mantle and the overlying recycled fertile crust of the Yunkai massif and ultimately to form the hybrid magma. This hybrid magma experienced different degrees of fractional crystallization to produce the wide compositional range of the Hudong gneissic composite pluton. We therefore conclude that the Hudong gneissic composite pluton was an important record of the oceanic subduction and subsequent continental collision in the northern margin of Yunkai massif during Early Paleozoic time. Source

Wu H.,Wuhan University | Zhang Y.-H.,Wuhan University | Ling W.-L.,Wuhan University | Bai X.,Wuhan University | And 4 more authors.
Precambrian Research | Year: 2016

Here we report a new study of a gabbroic suite and its associated dioritic and monzogranitic plutons situated in the Yangtze continental interior, the unique continental core in South China, by means of integrated U-Pb dating and Hf isotope analysis of zircon and whole rock Sr-Nd isotope and elemental geochemistry. These intrusive suites are parts of a large batholith (~970 km2) known as the Neoproterozoic Huangling intrusive complex, which is emplaced in the Archean to Paleoproterozoic high-grade terrain. The gabbro and diorite are dated at 812 ± 3 Ma and 816 ± 6 Ma, respectively, whereas the monzogranite is dated at 801 ± 6 Ma. Trace element geochemistry of magmatic clinopyroxene, peritectic hornblende and petrography of the gabbro suggest that the mafic suite formed by anhydrous melt that had undergone the early stages of crystalline fractionation of plagioclase, clinopyroxene and/or garnet. Zircon Hf isotope and whole-rock Sr-Nd isotopic and elemental compositions infer that the gabbro was sourced by slightly enriched lithospheric mantle modified by previous subduction; the diorite is likely to have been derived from ~850 Ma igneous rocks by anatexis and admixing variably with mantle-derived melt, whereas the monzogranite was dominantly sourced by the crystalline basement rocks. It is thus suggested that the associated igneous suites formed in a rift-related setting, and underplating of mantle-derived melt and mantle input had played a significant role during the magmatism. This plutonism event is synchronous with the initial deposition of widespread rift-basins in South China, which was succeeded by huge volumes of mid-late Neoproterozoic to Paleozoic sedimentary successions. These findings hence attest that the magmatism took place in a within-plate environment and a consecutively rift-related event was likely initiated at ~850 Ma. In the interior of the Yangtze block, which is also widely recorded along its northern, western and northeastern margins and in the Cathaysia block. © 2016 Elsevier B.V. Source

Mo J.,Natural History Museum of Guangxi | Zhou F.,Guangxi Institute of Regional Geological Survey | Li G.,Guangxi Institute of Regional Geological Survey | Huang Z.,Guangxi Institute of Regional Geological Survey | Cao C.,Guangxi Institute of Regional Geological Survey
Acta Geologica Sinica | Year: 2014

A new large-bodied theropod dinosaur, Datanglong guangxiensis gen. et sp. nov., was recovered from the Lower Cretaceous Xinlong Formation of the Datang Basin, Guangxi. It is unique in several features including: posteriormost dorsal vertebra with teardrop-shaped pneumatic foramen confined by enlarged pcdl, acpl and the centrum; posteriormost dorsal with well-developed, horizontal prpl; posteriormost dorsal with a parapophysis projecting more laterally than the diapophysis; brevis fossa shallow with short, ridge-like medial blade; and iliac pubic peduncle with posteroventrally expanded margin. Cladistic analysis supports the idea that this new taxon Datanglong guangxiensis is a primitive member of the Carcharodontosauria in possessing two unambiguous synapomorphies: large external pneumatic foramina and internal spaces present in the lateral surface of ilium, and a peg-and-socket ischiac articulation with the ilium. The presence of the new taxon from Guangxi further confirms that Carcharodontosauria were cosmopolitan large-bodied predators during the Early-mid Cretaceous. © 2014 Geological Society of China. Source

Qin X.,Guilin University of Technology | Qin X.,Chinese Academy of Geological Sciences | Wang Z.,Chinese Academy of Geological Sciences | Zhang Y.,Chinese Academy of Geological Sciences | And 3 more authors.
Acta Geologica Sinica | Year: 2012

The Napo-Qinzhou Tectonic Belt (NQTB) lies at the junction of the Yangtze, Cathaysia and Indochina (North Vietnam) Blocks, which is composed of five major lithotectonic subunits: the Qinzhou-Fangcheng Suture Zone (QFSZ), the Shiwandashan Basin (SB), the Pingxiang-Nanning Suture Zone (PNSZ), the Damingshan Block (DB) and the Babu-Lingma Suture Zone (BLSZ). On the basis of geochemical compositions, the Permian mafic igneous rocks can be divided into three distinct groups: (1) mafic igneous rocks (Group 1) from the Longjing region in the PNSZ and Hurun region in the BLSZ, which are characterized by intermediate Ti, P and Zr with low Ni and Cr contents; (2) mafic igneous rocks (Group 2) from the Naxiao and Chongzuo region in the DB, characterized by low-intermediate Ti, P and Zr with high Ni and Cr concentrations; and (3) mafic igneous rocks (Group 3) from the Siming region in the Jingxi carbonate platform of the northwestern margin of the NQTB, with intermediate-high Ti, P and Zr and low Ni and Cr contents. The Group 1 rocks yield a weighted mean 206Pb/ 238U age of 250.5±2.8 Ma and are geochemically similar to basalts occurring in back-arc basin settings. The Group 2 rocks exhibit geochemical features to those basalts in island arcs, whereas the Group 3 rocks show geochemical similarity to that of ocean island basalts. All three groups are characterized by relatively low ε Nd(t) values (-2.61 to +1.10) and high initial 87Sr/ 86Sr isotopic ratios (0.705309-0.707434), indicating that they were derived from a subduction-modified lithospheric mantle and experienced assimilation, fractional crystallization, and crustal contamination or mixing during magmatic evolution. Accordingly, we propose the existence of an arc-back arc basin system that developed along the NQTB at the border of SW Guangxi Province (SW China) and northern Vietnam, and it was formed by continued northwestward subduction of the Cathaysian (or Yunkai) Block under the Yangtze Block, and northeastward subduction of the Indochina Block beneath the Yangtze Block during Permian time. © 2012 Geological Society of China. Source

Yang L.-Z.,Guangxi Institute of Regional Geological Survey | Liu R.-T.,Guangxi Institute of Regional Geological Survey | Bai Y.-P.,Guilin University of Technology
Geological Bulletin of China | Year: 2011

According to the field geological characteristics and petrology of the Taima rock body (now known as Taima rockdome) which is the main body of Shiwandashan rock belt, the authors consider that the Taima rock body consist of porphyroclastic lavas and is an eruptive facies but not an intrusive phases of granite porphyries. Combined with the surrounding volcanic rocks, intrusive rocks and strata, the Taima rock body is considered as a dome of the central part of the central fissure type volcanic structure. Therefore, the Shiwandashan rock belt is a volcanic-intrusive complex rocks belt, and the Taima porphyroclasts lava is one of the phases in that belt. Source

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