Did the Indo-Asian collision alone create the Tibetan plateau?

Abstract

It is widely believed that the Tibetan plateau is a late Cenozoic feature produced by the Indo-Asian collision. However, because Tibet was the locus of continental accretion and subduction throughout the Mesozoic, crustal thickening during that time may also have contributed to growth of the plateau. This portion of the geologic history was investigated in a traverse through the central Lhasa block, southern Tibet. Together with earlier studies, our mapping and geochronological results show that the Lhasa block underwent little north-south shortening during the Cenozoic. Rather, our mapping shows that ~60% crustal shortening, perhaps due to the collision between the Lhasa and Qiangtang blocks, occurred during the Early Cretaceous. This observation implies that a significant portion of southern Tibet was raised to perhaps 3-4 km elevation prior to the Indo-Asian collision. INTRODUCTIONAlthough it has long been recognized that Tibet was the locus of continental collision and accretion since the early Mesozoic (Allégre et al., 1984;Sengör, 1984;Searle et al., 1987), the style and intensity of deformation produced by each accretional event remain poorly documented (e.g., Tibetan Bureau of Geology and Mineral Resources [TBGMR], 1982). To address this issue, we conducted systematic mapping of the Coqin area in the northcentral part of the Lhasa block ( Fig. 1), during which three thrust systems were documented (Gugu La, Shibaluo, and Emei La) along a 132-km-long north-south traverse (Fig. 2). None of these thrusts appear to have involved metamorphic basement, and thrusts in their hanging walls are cut by plutons that are in turn overlain by essentially flat-lying tuff deposits. Although the ages of sedimentary sequences in the mapped area have been broadly constrained as Paleozoic and Mesozoic by using index fossils (Tibetan Bureau of Geology and Mineral Resources, 1982), the igneous rocks were not previously dated. In this paper we briefly summarize the structural relationships and age constraints for the three thrusts and, in conjunction with allied data, conclude that the southern Tibetan plateau had begun to form during the Early Cretaceous and remained elevated until the Indo-Asian collision began. GUGU LA THRUST SYSTEMThe north-dipping Gugu La thrust places Cretaceous strata (Gugu La sequence) over Cretaceous (?) conglomerate and volcaniclastic rocks (Burial Hill sequence; Fig. 2a). The thrust has a maximum stratigraphic throw in its central part. Fault slickensides indicate a S10°-20°W transport direction.The lower part of the hanging wall consists of ~1-km-thick volcanic breccias and volcaniclastic sandstones. Paleocurrent measurements of crossbeds in the sandstone indicate a north-directed paleoflow. The top of the lower section (~800 m thick) is marked by a laterally extensive limestone layer, which contains abundant Early Cretaceous rudist bivalves (TBGMR, 1982). Above it is an ~500-m-thick sequence of fluvial sandstone that records a change upsection from north-directed to south-directed paleoflow. We inter...

Crustal–lithospheric structure and continental extrusion of Tibet

“…There is an increasing body of evidence that substantial crustal thickening and, by inference, surface uplift of Tibet may have occurred prior to the India-Asia collision (England & Searle 1986;Searle 1995;Murphy et al 1997;Kapp et al 2005Kapp et al , 2007aSpurlin et al 2005). Crustal thickening, folding and thrusting along the Bangong suture across central Tibet occurred during Early Cretaceous times.…”

“…Models for the growth of the Tibetan Plateau range from early, pre-India-Asia collision thickening and uplift in the Lhasa and southern Qiangtang blocks and Karakoram terrane (England & Searle 1986;Murphy et al 1997;Hildebrand et al 2001;Kapp et al 2005;Searle et al 2010a) through gradual uplift following the India-Asia collision (50-0 Ma) to sudden uplift at c. 7-8 Ma . The India-Asia collision itself must have been a continuing process since the Late Cretaceous-Early Palaeocene obduction of ophiolites onto the Indian passive continental margin and initial contact between Indian and Asian crust, through to final withdrawal of the Tethyan Ocean with ending of marine sedimentation in the Indus-Yarlung Tsangpo suture zone.…”

Large‐scale crustal deformation of the Tibetan Plateau

“…lision [Murphy et al, 1997] or that rapid uplift of most of the plateau is Pliocene-Quaternary in age [Che, 1986;Pan et al, 1990;Li, 1996]. In section 3 we describe a quantitative approach that we have developed to model the evolution of orogenic systems in three dimensions.…”

Geochemical variations in Miocene adakitic rocks from the western and eastern Lhasa terrane: Implications for lower crustal flow beneath the Southern Tibetan Plateau

“…It is generally accepted that the BNS formed during the Late JurassicMiddle Cretaceous (Yin and Harrison, 2000) and that the IYS formed during the Late Cretaceous-Early Paleogene (Dewey et al, 1988). The IYS marks the closure of the Tethys, and lies immediately south of an extensive Andean-type calc-alkaline magmatic center (Linzizong volcanics and Gangdese batholith) in the Lhasa terrane (e.g., Coulon et al, 1986;Mo et al, 2008;Murphy et al, 1997;Scharer et al, 1984). Since its collision with Asia at 50 Ma, the ongoing northward movement of India has led to thickening of the Tibetan crust, which is now twice the thickness of normal crust (Owens and Zandt, 1997;Zhao and Nelson, 1993).…”