Structures, Evolution And Tectonic Implications Of The Erlangping Group In North Qinling

Structures, evolution and tectonic implication of the Erlangping Group in North Qinling tectonic belt, central China, were systematically studied on the basis of plate tectonics through such modern techniques as microtectonics, c-axis petrafabrics of deformational quartz, electron microprobe microanalysis on muscovite composition, 40Ar/39Ar geochronological analysis, etc. Some new points were attained here.1. The alternative nature of strong and weak deformation is shown through three profiles across the Erlangping Group. Three tectonic slabs with distinct constituents, metamorphic assemblages and deformation structures and bounded by high strain zones are figured out and named the Erjingou slab, the Huoshenmiao slab, and the Baoshuping slab from north to south, respectively.2. The Xiaozhai-Erlangping and the Damiao-Wantan shear zones are discovered inside the Erlangping Group. The Xiaozhai-Erlangping shear zone has a two stage history, an earlier high angle pure shear shortening in N-S direction and a later WNW-ESE dextral shear no later than 110 Ma. The Damiao-Wantan shear zone has also experienced two events, including an earlier pure shear shortening in N-S direction and a later mid- to high temperature and high pressure dextral slip in WNW-ESE direction occurred no later than 100 Ma.3. The Zhuyangguan-Xiaguan and the Waxuezi-Qiaoduan shear zones on both sides of the Erlangping Group are investigated. The Zhuxia shear zone experienced two tectonic events, including an earlier mid- to high temperature shortening in N-S direction and a later medium temperature dextral shear no later than 104.7±0.5Ma in WNW-ESE direction. The Waxuezi-Qiaoduan shear zone also underwent two periods of ductile deformation, an earlier high temperature and a later mid- temperature high pressure dextral slip in WNW-ESE direction occurred no later than 120 Ma.4. The importance of dextral ductile shearing and the tectono-magmatic event in Mesozoic in North Qinling were emphasized. A Ar-Ar plateau age of muscovite grains(from Qinkou, north to Xixia) reveals that the Shangdan ductile shearing occurred no later than 319±1.4Ma. The Ar-Ar plateau age with 104.7±0.5Ma of biotite grains (from Matiwan) give close to the final stage of NWW-SEE dextral slip along the Zhuxia ductile shear zone.5. The amalgamation of the three slabs are discussed. During the Yanshanian period in Mesozoic, these three slabs are amalgamated to form its prestent configuration by clockwise shearing along shear zones.