Structural anatomy of the exhumation of high‐pressure rocks: constraints from the Tongbai Collisional Orogen and surrounding units

Abstract

The Tongbai Collisional Orogen and associated units, located between the Qinling and Dabie orogens, can be divided into nine lithotectonic units. From north to south, these are the southern tectonic unit of the North China Plate-the Maoji Group, the Erlangping tectonic unit, the Qinling Complex unit, the Guishan and Nanwan slice, the Xiaojiamiao mélange unit, the northern high-pressure (HP) unit, the Tongbai highgrade Complex, the southern HP unit and the Suizhou tectonic belt. Based on structural analysis and available geochronological data, five principal episodes of deformation (D 1 -D 5 ) are distinguished in this area following the Mesozoic HP metamorphism. The first two episodes of deformation developed in various tectonic units to the south of the Xiaojiamiao mélange unit, and the subsequent episodes of deformation developed in all the units of this area. The D 1 deformation is correlated to ca. 255-238 Ma generating regional penetrative foliation and WNW-trending stretching lineation, and leading to the initial stage of eastward oblique extrusion of the HP rocks. The D 2 event is characterized by top-to-the-SSW thrusting which contributed to the further vertical uplift of the HP rocks sometime around 230-215 Ma. The D 3 event is defined by WNW-trending open folds, and must have taken place earlier than Lower Jurassic. The D 4 event is characterized by ductile strike-slip shearing, and during this episode the Tongbai high-grade Complex was extruded to the east at ca. 131-119 Ma. The D 5 event probably took place at ca. 100-80 Ma, and is marked by the NW and NE trending brittle faults which overprint all of the above mentioned structures. The exhumation of the Tongbai HP rocks illustrates the process of gradual extrusion and uplift, controlled by several episodes of deformation.

Intracontinental deformation in a frontier of super-convergence: A perspective on the tectonic milieu of the South China Block

“…1) and the nearly east-west-trending West KunlunEast Kunlun-West Qinling-East Qinling-Tongbai-Dabie-Sulu Orogen (also called the Central China Orogen, CCO in Fig. 1, Li et al, ,b, 2010aLiu et al, 2011a). The first quadrant is the North China Craton (also called the North China Block), the second quadrant is the Tarim Block or Basin and related basin-mountain system, and the third quadrant is the central-southern part of the Qinghai-Tibet Plateau and the fourth quadrant is the South China Block (Fig.…”

“…To the south of the Qinling Orogen, a near E-W-striking, narrow foreland accretionaly prism was formed through the collision between the South China and the North China blocks along the Dabie-Sulu Orogen. The earliest time of northward subduction of the South China Block is earlier than 244 Ma, while the collision time is 226 Ma Liu et al, 2011a;. Because the northern part of the Yangtze Block was proximal to the collisional belt, the effect of the collision was much pronounced, dominated by near E-W-striking structures.…”

Diachroneity of continental subduction and exhumation: Constraints from the Permian-Triassic HP metamorphic terrane in the Tongbai orogen, central China

“…The metamorphic volcanic-sedimentary rocks with a better sequence in this zone may represent surficial rocks deposited on the northern margin of the South China Block. These rocks structurally show south-dipping in the Hong'an orogen [4] and top-to-the-south thrusting in the Tongbai orogen [43]. Therefore, the blueschist-greenschist zone was regarded as a large-scale nappe extruded from the northern suture in our tectonic model [5,38].…”

Tectonic evolution of the Tongbai-Hong’an orogen in central China: From oceanic subduction/accretion to continent-continent collision

“…The strike-slip directions of the shear zones are opposite, being dextral for the southern boundary, and sinistral for the northern boundary. On the eastern end of the complex, a south-north stretching thrust ductile shear zone occurs (Webb et al, 1999(Webb et al, , 2001Liu X et al, 2011;Cui et al, 2012). Therefore, the Tongbai Complex is actually surrounded by a huge ductile shear zone streching alone the orogen.…”