Geochemical characteristics and LA- ICP-MS age of zircons from the Luohanshi Formation mafic volcanic rocks, North Qinling: Evidence for Paleozoic subduction-accretion Process in the Qinling Orogen

Content Provider	Semantic Scholar
Author	Chen, Leiming Ji＇an Zheng, Shu Zhang, Xin
Copyright Year	2010
Abstract	The Shangdan Ophiolitic Tectonic Mélange zone is an important plate subduction-accretion zone that is located in the southern margin of the North Qinling Belt. Luohanshi Formation as one key elements occurs along the south frank of the Shangdan Ophiolitic Tectonic Mélange zone and comprises fine-grained sandstones with interbeds of volcanic and volcaniclastic rocks and carbonates. Locally, wedgeshaped deposits, which contain conglomerate-bearing sandstones, sand conglomerates and conglomerates, develop. It exhibits the fault contact with the Danfeng Group to the north and Liuling Group to the south. In this study, wholerock major-trace elements and zircon U-Pb isotope compositions are presented for mafic volcanic rocks from the Luohanshi Formation in the North Qinling Belt. Two selected samples yield zircon U-Pb ages of 389.4Ma (MSWD = 0.31) and 397.7Ma (MSWD = 1.4), implying the Luohanshi Formation form at Devonian. Geochemically, these mafic rocks have SiO2=49.59~50.64, Al2O3!15.5, K2O/Na2O= 0.90~1.03, K2O=1.50~3.08, typical of shoshonite series. In addition, they are characterized by continental arc-like patterns of trace element distribution, with enrichment in strong and medium incompatible elements (except for element Sr) but depletion in weak incompatible elements such as Sm, Y and Yb on N-MORB normalized diagrams. Their REEs patterns are also similar to those of continental arc, characterized by low ,REE varying from118.43ppm to 125.84 ppm, fractionated REE patterns ((La/Yb)n ranging from 8.34 to 9.73), and weak to no Eu anomalies (Eu/Eu* = 0.97 ~ 1.01). Integrated with the regional geological features, we can infer that the Luohanshi Formation volcanic rocks probably are interpreted as an accretion arc. In this case, subduction during late-Palaeozoic would give rise to the volcanic rocks of the Luohanshi Formation. Therefore, the Devonian mafic rocks provide the important petrological record of subduction-accretion processes during the latePalaeozoic North Qinling Orogen.
File Format	PDF HTM / HTML
Alternate Webpage(s)	https://goldschmidtabstracts.info/2010/170.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article