The thickness and structural characteristics of the crust across Tibetan plateau from active-sources seismic profiles

Abstract

The Tibetan plateau as one of the youngest orogen on the Earth was considered as the result of continent-continent collision between the Eurasian and Indian plates. The thickness and structure of the crust beneath Tibetan plateau is essential to understand deformation behavior of the plateau. Active-source seismic profiling is most available geophysical method for imaging the structure of the continental crust. The results from more than 25 active-sources seismic profiles carried out in the past twenty years were reviewed in this article. A preliminary cross crustal pattern of the Tibetan Plateau was presented and discussed. The Moho discontinuity buries at the range of 60−80 km on average and have steep ramps located roughly beneath the sutures that are compatible with the successive stacking/accretion of the former Cenozoic blocks northeastward. The deepest Moho (near 80 km) appears closely near IYS and the crustal scale thrust system beneath southern margin of Tibetan plateau suggests strong dependence on collision and non-distributed deformation there. However, the ~20 km order of Moho offsets hardly reappears in the inline section across northern Tibetan plateau. Without a universally accepted, convincing dynamic explanation model accommodated the all of the facts seen in controlled seismic sections, but vertical thickening and northeastern shorten of the crust is quite evident and interpretable to a certain extent as the result of continent-continent collision. Simultaneously, weak geophysical signature of the BNS suggests that convergence has been accommodated perhaps partially through pure-shear thickening accompanied by removal of lower crustal material by lateral escape. Recent years the result of Moho with ~7 km offset and long extend in south-dip angle beneath the east Kunlun orogen and a grand thrust fault at the northern margin of Qilian orogen has attract more attention to action from the northern blocks. The broad lower-velocity area in the upper-middle crust of the Lhasa block was once considered as resulted from partially melted rocks. However the low normal v P /v S ratio and the Moho stepwise rise fail to support significant partial melting in the middle-lower crust of the central-northern Tibetan plateau. Furthermore, the lower-velocity of crust occasionally disappears, and/or local thinned exhibits their non-stationary spatial distribution.

Lithospheric Structure of Eastern Tibetan Plateau from Terrestrial and Satellite Gravity Data Modeling: Implication for Asthenospheric Underplating

“…We get similar values for the western part of the Tibetan plateau in our gravity models. All the values match the crustal thicknesses suggested by Li et al [130]. Apart from slight differences in Moho depth around the ITSZ, we do not see crustal thinning close to the collision zone.…”

An overview of the crustal structure of the Tibetan plateau after 35 years of deep seismic soundings

“…(Molnar and Deng, 1984;Molnar et al, 1983Molnar et al, , 1987Besse et al, 1984;Besse and Courtillot, 1991;Le Pichon et al, 1992;Avouac and Tapponnier, 1993;Holt et al, 1995;Peltzer and Saucier, 1996;England and Molnar, 1997;Royden et al, 1997;Larson et al, 1997Larson et al, , 1999Yang et al, 1998Yang et al, , 2001Wang et al, 2001;Yang, 2002;Replumaz and Tapponnier, 2003). The thickening of the Tibetan crust to about twice the normal thickness occurred by northward migration, north-south shortening and vertical stretching of Asia by India in the course of the Middle Eocene to the Early Miocene (Zeng et al, 1996;Li et al, 2009). Since this epoch the northward movement of India has been accommodated principally by north-south shortening in the north and south of Tibet.…”

Constraining the Jurassic extent of Greater India: Tectonic evolution of the West Australian margin

“…Seismic data show that the Himalayas are composed of stacked continental crust [ Searle et al , 1987] approximately 65–80 km thick [ Hirn , 1988; Li et al , 2009; Teng , 1987], while the Indian crust south of the Himalayas is only about 35 km thick [ Zhang et al , 2007]. Models that derive crustal shortening estimates from balancing lithological cross‐sections from the India‐Eurasian collision zone, between Himalaya and Tibet, often result in the smallest estimates for the minimal extent of Greater India, such as 536 km [ Ratschbacher et al , 1994].…”