The Geochemistry Of The Yinggezui Ophiolitic Mélange In The West Northern Qinling Belt, And Its Tectonic Implications

Yinggezui Ophiolitic Melange (YGOM) is situated in Meixian county, and overthrusted into the west part of the Shangdan suture zone. It represents the early Paleozoic relics of the suture zone between the North China Block (NCB) and Yangtze Block (YZB). It is a key to understand the tectonic evolution of the paleo-ocean extension, and the subduction, collision between the NCB and YZB. Based on the combined studies on the structural geology and geochemistry, and contrast with the Erlangping ophiolite and Danfeng, ophiolite, the property, tectonic setting and implications of the YGOM has been discussed in this paper,1 The YGOM can be divided into southern and northern parts, which is mainly of ophiolotic assemblage and volcanic-sedimentary assemblage, respectively. The ophiolitic assemblage is composed of basic lavas, gabbros, peridotites and serpentinites. While, the volcanic-sedimentary assemblage includes of basaltic andesites, intermediate-acidic volcanic and clastic rocks, with a miner of basalts.2 The geochemistry of the basalts from the ophiolitic suite is characterized by depleted in LREE, low ZREE and unfractionation in HFSE, which is similar to that of MORB. It is indicate that the basalts were derived from a depleted mantle in an extending tectonic setting. The intermediate lava of the northern assemblage is characterized by enriched in LREE, LILE and depleted in HFSE, especially depleted in Nb and Ta. These geochemical characteristics suggest that its magma source was influenced by inputs of the subduction components. All above evidence suggests that the Yinggezui ophiolitic melange was formed in a tectonic setting related to the subduction between the NCB and YZB.3 Yinggezui ophiolitic melange include not only the ophiolite with typical geochemistry similar to MORB, but also the intermediate-acidic volcanic rocks andclastic rocks which is related to the subduction event.4 Based on the comprehensive studies on geology and geochemistry of the collected geochemistry data of Danfeng volcanic rocks which is situated in Heihe, Shangxian, Danfeng, Shangnan, et region, the geochemistry of the Danfeng Basalt was studied, which suggests that the Danfeng volcanic rocks was formed in an island-arc setting related to the subduction between the NCB and YZB.5 On the Bases of the study on the collected the geochemical data of Erlangping volcanic rocks from western of the Henan province, the Erlangping volcanic rocks are identified that formed in a back-arc basin setting.6 Contrast with the regional geology, it is indicated that Yinggezui ophiolitic melange is formed in a back-arc basin setting, which is similar to Erlangping ophiolite. Volcanic-sedimentary assemblage of the northern melange was formed in the early stage of the expanding of the back-arc basin.