Multiple Emplacement and Exhumation History of the Late Mesozoic Dayunshan–Mufushan Batholith in Southeast China and Its Tectonic Significance: 1. Structural Analysis and Geochronological Constraints

Abstract

The South China Block (SCB) experienced a polyphase reworking by the Phanerozoic tectonothermal events. To better understand its Late Mesozoic tectonics, an integrated multidisciplinary investigation has been conducted on the Dayunshan–Mufushan composite batholith in the north‐central SCB. This batholith consists of two major intrusions that recorded distinct emplacement features. According to our structural analysis, two deformation events in relation to batholith emplacement and subsequent exhumation are identified. The early one (D1) was observed mostly at the southern border of the batholith, characterized by a top‐to‐the‐SW ductile shearing in the early‐stage intrusion and along its contact zone. This deformation, chiefly associated with the pluton emplacement at ca. 150 Ma, was probably assisted by farfield compression from the northern Yangtze foreland belt. The second but main event (D2) involved two phases: (1) ductile shearing (D2a) prominently expressed along the Dayunshan detachment fault at the western border of the batholith where the syntectonic late‐stage intrusion and minor metasedimentary basement in the footwall suffered mylonitization with top‐to‐the‐NW kinematics; and (2) subsequent brittle faulting (D2b) further exhumed the entire batholith that behaved as rift shoulder with half‐graben basins developed on its both sides. Geochronological constraints show that the crustal ductile extension occurred during 132–95 Ma. Such a Cretaceous NW–SE extensional tectonic regime, as indicated by the D2 event, has been recognized in a vast area of East Asia. This tectonism was responsible not only for the destruction of the North China craton but also for the formation of the so‐called “southeast China basin and range tectonics.”

Cretaceous Episodic Extension in the South China Block, East Asia: Evidence From the Yuechengling Massif of Central South China

“…Hongzhen‐HZ (Zhu, Xie, et al, ); 13. Dayunshan‐DYS (Ji, Lin, Faure, Chen, et al, ; Ji, Faure, et al, ); 14. Lushan‐LS (Lin et al, ; Liu et al, ; Wang et al, ; Yang et al, ; Zhu, Yang, et al, ); 15.…”

“…In contrast to the northern region, the two‐stage evolution model plays a more important role in those more southerly extensional domes (Figure ), that is, Dayunshan (DYS), Lushan (LS), Hengshan (HS), and Yuechengling (YCL), and dictates different rock deformation patterns in response to the two events. The DYS and HS domes are both characterized by NW‐SE stretching with a top‐to‐the NW shear sense, and the detachments were active between 140 and ~85 Ma (Ji et al, ; Ji, Faure, et al, ; Li et al, , ). Although the possibility of a long‐lived detachment cannot be excluded, the cooling age patterns exhibit a ~20‐Myr interval between the two age peaks (Figure a), implying intermittent movement of the detachments.…”

“…Contemporaneous with the Cretaceous magmatism, detachments or high‐angle normal faults controlled most extensional basins in which continental red beds were deposited (Shu et al, ). Some pretectonic and syntectonic granitic plutons were also deformed under subsolidus conditions by these detachments (Ji, Faure, et al, ; Wei et al, ), but most of the structures can be classified as extensional domes/MCCs (Figure ), including Hengshan (Li et al, ; Wei et al, ), Lushan (Lin et al, ; Zhu, Xie, et al, ), Hongzhen (Zhu, Yang, & Wang, ), Wugongshan (Faure et al, ), and Yuechengling, which were subjected into pervasive ductile deformation. However, two kinematics include NE‐SW and NW‐SE stretching characterize those extensional structures (Ji, Faure, et al, ; Li et al, ; Zhu, Xie, et al, ), indicating a heterogeneous pattern that accommodates the large‐scale crustal extension.…”

“…Despite intermittent short‐lived compression, extensional structures dominated the tectonic framework of the Late Mesozoic SCB, including (half‐) graben basins and brittle normal faults or detachments (Li et al, ; Shu et al, ). Recent studies have reported several detachments within MCCs or extensional domes in this region, and those detailed work on field mapping, structural analysis, and geochronological/thermochronological dating constrain the deformation pattern and episodes of activities of those detachments (Ji et al, ; Li et al, ; Wei et al, ; Zhu, Xie, et al, ).…”

“…To better recover the general history of extension in the SCB, the knowledge of timing, kinematics, exhumation amount and rate, and spatial variation is critical. However, compared with the well‐constrained tectonic evolution of the MCCs in the NCB (Lin et al, ; Lin, Faure, et al, ; Liu et al, ; Wang et al, ; Zhu et al, ), not only variable kinematics has been demonstrated in different MCCs/domes of the SCB (e.g., Faure et al, ; Lin et al, ; Zhu, Xie, et al, ; Li et al, ; Wei et al, ; Ji, Faure, et al, ), but the temporal‐spatial distribution of extensional structures also provides a more complex story that contains episodic deformation with ill‐defined boundaries of this extensional province (Ji et al, ; Figure ). Notwithstanding the complication of the Late Mesozoic tectonics in the SCB, more pieces of evidence are accumulated with the timing, amount, and geodynamic setting of extension than were known before.…”