Structural mapping and special structural analysis allow the recognition of a previously unidentified tectonic boundary between two distinct metamorphic terrains in the eastern Qinling mountains. The boundary crops out in the northern part of the Xixia and Neixiang, Henan Province in a WNW-trending zone roughly 100 km long and 2 km wide that narrows to wards northwest. The Proterozoic Qinling Group gneisses and marbles are separated from the Paleozoic lowmetamorphic volcanic rocks and turbidite sequence by the boundary. The boundary which can be called the Junmahe-Matiwan Fault Belt is a major ductile thrust zone. It is marked by mylonitic rocks and straight gneisses. Thick marble units in this zone invaribly have the form of tectonic melange, full of rotated and flattened blocks or fragments of various types of granites, silicalites, dolomites, etc. in a mylonitic matrix. The mylonitic foliation within this zone dips gently to the south. It is folded and truncated by younger ductile or brittle shear zones. The kinematic evidence afforded by the major ductile shear zone leads to a model for development of the eastern Qinling mountains through a process of stacking of crustal segments, with translation northward along lo-wangle ductile shear zones originating at considerable depth. The boundary is actually a basal ductile defomation zone, along which the reworked Proterozoic metamorphic belt has been thrusted to the north on the Paleozoic metamorphic belt before emplacement of the Mesozoic granitoids. Thus these new data are clearly favorable to the intracontinental shearing model.
Suo Shutian,Zhong Zengqiu,Hu Yuhua. TECTONIC BOUNDARY BETWEEN PROTEROZOIC AND PALEOZOIC TERRAINS IN THE NORTHERN PART OF THE XIXIA AND NEIXIANG, HENAN PROVINCE[J]. Chinese Journal of Geology, 1990, (1): 12-21.