New constraints on the structure, thermochronology, and timing of the Ailao Shan‐Red River shear zone, SE Asia

Abstract

New structural, petrographic, and 40Ar/39Ar data constrain the kinematics of the ASRR (Ailao Shan‐Red River shear zone). In the XueLong Shan (XLS), geochronological data reveal Triassic, Early Tertiary, and Oligo‐Miocene thermal events. The latter event (33–26 Ma) corresponds to cooling during left‐lateral shear. In the FanSiPan (FSP) range, thrusting of the SaPa nappe, linked to left‐lateral deformation, and cooling of the FSP granite occurred at ≈35 Ma. Rapid cooling resumed at 25–29 Ma as a result of uplift within the transtensive ASRR. In the DayNuiConVoi (DNCV), foliation trends NW‐SE, but is deflected near large‐scale shear planes. Stretching lineation is nearly horizontal. On steep foliations, shear criteria indicate left‐lateral shear sense. Zones with flatter foliations show compatible shear senses. Petrographic data indicate decompression from ≈6.5 kbar during left‐lateral shear (temperatures >700°C). 40Ar/39Ar data imply rapid cooling from above 350°C to below 150°C between 25 and 22 Ma without diachronism along strike. Along the whole ASRR cooling histories show two main episodes: (1) rapid cooling from peak metamorphism during left‐lateral shear; (2) rapid cooling from greenschist conditions during right‐lateral reactivation of the ASRR. In the NW part of the ASRR (XLS, Diancang Shan), we link rapid cooling 1 to local denudations in a transpressive environment. In the SW part (Ailao Shan and DNCV), cooling 1 resulted from regional denudation by zipper‐like tectonics in a transtensive regime. The induced cooling diachronism observed in the Ailao Shan suggests left‐lateral rates of 4 to 5 cm/yr from 27 Ma until ≈17 Ma. DNCV rocks always stayed in a transtensive regime and do not show cooling diachronism. The similarities of deformation kinematics along the ASRR and in the South China Sea confirms the causal link between continental strike‐slip faulting and marginal basin opening.

Zircon U-Pb geochronology and heavy mineral composition constraints on the provenance of the middle Miocene deep-water reservoir sedimentary rocks in the Yinggehai-Song Hong Basin, South China Sea

“…Cenozoic zircon grains with age peak at ca. 35 Ma could be derived from the Red River Fault Zone where several large and small plutonic bodies of this age exist (Sch€ arer et al, 1990;Leloup et al, 1995Leloup et al, , 2001Chung et al, 1997). Sample H29-6 contains numerous grains about 34 Ma suggesting more detritus from the Red River Fault Zone.…”

Provenance of Upper Miocene to Quaternary sediments in the Yinggehai-Song Hong Basin, South China Sea: Evidence from detrital zircon U–Pb ages

“…32 Ma) in different samples imply a source from the Red River Fault Zone in southern Yangtze Craton with the high-grade metamorphic rocks, which have been dated in the range of 20-60 Ma (Fig. 8A) (Zhang and Schärer, 1999;Leloup et al, 2001;Gilley et al, 2003). The age range and extremely narrow distribution of grains are related to melting and exhumation triggered by motion on the Red River Fault Zone (Hoang et al, 2009;Liu et al, 2013).…”

Crustal–lithospheric structure and continental extrusion of Tibet

“…Evidence for larger offsets (c. 400 km) along the Altyn Tagh Fault, however, does appear to be more robust (Yue et al 2003Zhang et al 2001;Cowgill et al 2003). Leloup et al (2001) and Replumaz & Tapponnier (2003) illustrating the continental extrusion model. (c) Plasticine experiments showing plane strain indentation of a rigid Indian indenter into a layered plasticine block with a free boundary on the eastern side, after Tapponnier et al (1982) and Peltzer & Tapponnier (1988).…”

“…This model has been vigorously promoted by many researchers working both in Tibet (e.g. Tapponnier et al 1982Tapponnier et al , 2001bPeltzer & Tapponnier 1988;Armijo et al 1989;Avouac & Tapponnier 1993) and in SE Asia (Leloup et al , 1995(Leloup et al , 2001Lacassin et al 2004a). …”