Structure, age, and tectonic development of the Huoshishan-Niujuanzi ophiolitic m茅lange, Beishan, southernmost Altaids
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- 作者：Zhonghua Tian ; Wenjiao Xiao ; Brian F. Windley ; Li'na Lin ; Chunming Han ; Ji'en Zhang ; Bo Wan ; Songjian Ao ; Dongfang Song ; Jianyun Feng
- 关键词：Arc-type ophiolitic mé ; lange ; South-dipping subduction ; Zircon U&ndash ; Pb dating ; Beishan Orogenic Belt ; Altaids
- 刊名：Gondwana Research
- 出版年：March, 2014
- 年：2014
- 卷：25
- 期：2
- 页码：820-841
- 全文大小：6289 K
文摘
The Huoshishan-Niujuanzi ophiolitic m茅lange (HNO) is located near the central part of the Beishan Orogenic Belt in the southernmost Altaids. The HNO consists of ultramafic rocks, cumulate gabbros, gabbros, plagiogranites, diorites, diabases, basalts, andesites, rhyolitic volcaniclastic rocks and siliceous sedimentary rocks, many of which are in a schist matrix (Gongpoquan Group). Geochemical data of the mafic rocks indicate a calc-alkaline or a mixture of calc-alkaline and tholeiitic rocks with negative Nb, Ta and positive Pb, Ba and La anomalies, suggesting formation in an island arc or supra-subduction zone setting. A gabbro from a block in the m茅lange in the Niujuanzi area has a zircon age of 435.0 卤 1.9 Ma and a plagiogranite with an age of 444.3 卤 1.9 Ma, and another gabbro from the Huoshishan area has an age of 410.5 卤 3.7 Ma. The schist matrix has a zircon age of 512 卤 5.3 Ma and contains Silurian, Devonian and Carboniferous fossils, thus the m茅lange formed in the late Carboniferous or later. Our structural analysis of fault planes in the HNO, the crenulation cleavages (S2) of the schist, and fold axial planes of early Permian sandy limestone/quartz veins and late Permian sandstones indicates that the m茅lange underwent a north-to-south compression, and the orientation of stretching lineations, slickensides and fold hinge lines implies that the HNO experienced top-to-the north (or -northwest) movement. The entire planar and linear structural data set suggests that the subduction polarity was probably to the south in the late Paleozoic. The emplacement age of the HNO was probably near the end-Permian based on the age of the youngest rocks in the ophiolitic m茅lange, and by the presence of a late Permian unconformity. From our work, integrated with published regional data, we outline a comprehensive geodynamic model for the central BOC.