LA-ICP-MS Zircon U-Pb Geochronology of Volcanic Rocks in the Shuangqiaoshan Group at Anhui-Jiangxi Boundary Region and Its Geological Implication
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The low-grade metamorphic andesite, rhyolite and tuff are found in the Shuangqiaoshan Group in the Qimen-Pingli area at the Anhui-Jiangxi border region. In this study, we present LA-ICP-MS U-Pb zircon dating and geochemical analysis results for the volcanic rocks found in the Shuangqiaoshan Group. The LA-ICP-MS zircon U-Pb dating shows that these volcanic rocks were formed at (822.4±6.0) Ma, (821.2±4.6) Ma and (830.4±4.9) Ma, which indicates an early Neoproterozoic age of the Shuangqiaoshan Group. In geochemical composition, these volcanic rocks are mainly moderately potassium calc-alkaline, relatively LREE enriched, HREE and HFSE high field strength elements (Nb, Ta and Ti) depleted, and likely were formed in the island arc environment. Whole rock Nd isotope study shows that the andesite was derived by partial melting of subducted oceanic crust and mantle-derived materials contributed to generation of rhyolite and tuff. Combining with the regional geological information, we believe that the volcanic rocks in the Shuangqiaoshan group at the Anhui-Jiangxi border region geodynamically coincide with freguently occurred magmatic activities in South China for the same period (838 Ma-820 Ma). Another word, these volcanic rocks were the results of island arc magmatism at that time.Keywords:
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Precise in situ zircon U-Pb dating and Lu–Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr–Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE(e.g. Th, U, Pb and La) and depletion of HFSE(e.g. Nb, Ta, Ti, Zr and Hf). Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr(0.703457 to 0.708218) and eNd(t)(-2 to 5.8) indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-eNd(t) diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon eHf(t) values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores(2616±39 Ma and 1297±22 Ma). The mineralization of the Tongyu copper deposit shows syn-volcanic characteristics such as layered orebodies interbedded with the volcanic rock strata, thus, the zircon U-Pb age of the volcanic host rocks can approximately represent the mineralization age of the Tongyu copper deposit. Both the Meigou pluton and the volcanic host rocks were formed during the ca. 440 Ma northward subduction of the Paleo-Qinling Ocean when high oxygen fugacity aqueous hydrothermal fluid released by dehydration of the slab and the overlying sediments fluxed into the mantle wedge, triggered partial melting of the mantle wedge, and activated and extracted Cu and other ore-forming elements. The magma and ore-bearing fluid upwelled and erupted, and consequently formed the island arc volcanic rock suite and the Tongyu VHMS-type copper deposit.
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The early Devonian strata in Malasu area is a set of littoral-neritic facies volcanic sedimentary rocks. This paper reports the zircon age and geochemical characteristics of the volcanic rocks. A lot of Neo-Archean and middle Neo-Proterozoic zircons indicate that this area contains ancient continental crust material. According to the values of major elements(Si O252.38%~69.6%, Na2 O 2.80%~4.85%, K2 O 0.16%~0.96%, Ti O20.5%~1.96%, Al2O314.62%~18.18%, Mg O 1.08%~5.75%) and the values of Mg#(22.92~38), the volcanic rocks of Malasu area are characterized by high content of sodium and low content of potassium, and thus belong to low-potassium tholeiite series and calc-alkaline series. The volcanic rocks have significant negative Eu anomalies(0.83~0.83), total rare earth element values of 73×10-6~115×10-6, and LREE/HREE values of 2.66~3.25. The geochemical characteristics of basaltic andesite samples are similar to those of typical volcanic arc basalts, being rich in large ion lithophile elements K, Rb, Ba, Sr and depleted in the high field strength elements Nb, Ta, Zr, Hf. The same characteristics of enrichment of LILE and depletion of HFSE for dacite por-phyry samples reflect the addition of lots of crust-derived materials. The chondrite-normalized REE and primitive mantle-normalized alteration-resistant trace element patterns for the dacite porphyry are similar to the patterns of basaltic andesite, which suggests that they belong to the comagmatic evolutionary series. Comprehensive research shows that the volcanic rocks have the characteristics of island arc volcanic rocks, and were formed in the volcanic island arc environment in the process of plate subduction.
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Research Article| August 01, 1991 Magmatism along the southeast margin of the Yangtze block: Precambrian collision of the Yangtze and Cathysia blocks of China Chen Jiangfeng; Chen Jiangfeng 1Department of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China Search for other works by this author on: GSW Google Scholar K. A. Foland; K. A. Foland 2Department of Geology and Mineralogy, Ohio State University, Columbus, Ohio 43210 Search for other works by this author on: GSW Google Scholar Xing Fengming; Xing Fengming 3Anhui Institute of Geological Sciences, Hefei, Anhui 230001, China Search for other works by this author on: GSW Google Scholar Xu Xiang; Xu Xiang 3Anhui Institute of Geological Sciences, Hefei, Anhui 230001, China Search for other works by this author on: GSW Google Scholar Zhou Taixi Zhou Taixi 1Department of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China Search for other works by this author on: GSW Google Scholar Author and Article Information Chen Jiangfeng 1Department of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China K. A. Foland 2Department of Geology and Mineralogy, Ohio State University, Columbus, Ohio 43210 Xing Fengming 3Anhui Institute of Geological Sciences, Hefei, Anhui 230001, China Xu Xiang 3Anhui Institute of Geological Sciences, Hefei, Anhui 230001, China Zhou Taixi 1Department of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1991) 19 (8): 815–818. https://doi.org/10.1130/0091-7613(1991)019<0815:MATSMO>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Chen Jiangfeng, K. A. Foland, Xing Fengming, Xu Xiang, Zhou Taixi; Magmatism along the southeast margin of the Yangtze block: Precambrian collision of the Yangtze and Cathysia blocks of China. Geology 1991;; 19 (8): 815–818. doi: https://doi.org/10.1130/0091-7613(1991)019<0815:MATSMO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The time and the environment of formation of igneous rocks along the southern margin of the Yangtze continental block in southern Anhui Province and northeastern Jiangxi Province, China, are discussed. Sm-Nd dating for samples from two ophiolite suites give ages of about 1 Ga. Late Proterozoic granodiorites in the study area have ages of about 0.9 Ga and have normal intrusive relations against Banxi Group metamorphic country rocks. Trace element abundances and initial Nd isotope ratios for ophiolite and Proterozoic granodiorites are consistent with formation in an island-arc environment. In contrast, Sr and Nd isotopes for Mesozoic granitoids of the region suggest that they are products of remelting of crustal sources similar to the basement of the Yangtze block. These relations do not support a recently proposed Mesozoic overthrust tectonic model for southeast China, but rather favor a late Precambrian collision history for the Yangtze and Cathysia blocks. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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