Crustal Density Structure, Lithosphere Flexure Mechanism, and Isostatic State Throughout the Qinling Orogen Revealed by In Situ Dense Gravity Observations

Abstract

Gravity and GPS hybrid measurements were conducted at 385 stations throughout the Qinling Orogen, China, to update Bouguer gravity anomalies and free‐air gravity anomalies of the area. The crustal density structure, lithosphere flexure mechanism, and isostatic state of the Qinglin Orogen were studied in detail via these in situ observations. Bouguer gravity anomalies in the study area are mainly negative, ranging from −410 mGal in the Tibetan Plateau to −100 mGal in the eastern Qinglin Orogen. The estimated crustal thickness ranges from 56 to 35 km and thins eastward along the Qinling Orogen. The optimal effective elastic thickness (Te) of the study area is 14 km, and the loading comes from the Earth's surface, the interface between the upper and lower crust, and the Moho. Vertical tectonic stress borne by the lithosphere varies observably in the study area. Downward stress reaches a peak of −14 MPa in the Liupanshan Mountains, whereas the highest value of upward stress (8 MPa) is attained in the middle Qinling Orogen. Considering distributions of crustal density structures and vertical tectonic stress of the lithosphere, in addition to the distinct loading ratios of the eastern and western Qinling Orogen, a piecewise combination model was developed to interpret the uplift of the Qinling Orogen. This model shows that the eastern part of the Orogen is thickened by the upward migration of mantle materials under the thrusting of the South and North China Blocks, whereas uplift of the western part results from lower crustal flow derived from the Tibetan Plateau.

A global reference model of the lithosphere and upper mantle from joint inversion and analysis of multiple data sets

“…A comparison with higher-resolution density models in different parts of the world (e.g. Kozlovskaya et al 2004;Yegorova et al 2013;Hasterok & Gard 2016;Gradmann et al 2017;Sippel et al 2017;Alghamdi et al 2018;Wang et al 2018) shows a close agreement with our crustal density values.…”

Uplift Mechanism of the Highest Mountains at Eastern Himalayan Syntaxis Revealed by In Situ Dense Gravimetry

“…The observation and data procedure methods follow our previous studies (Fu et al, 2014; Fu & She, 2017; Wang et al, 2018). Two Burris gravimeters (B105 and B115) were used to carry out the data on gravity.…”

“…Hu and Yao (2018) compared their Vs velocity results with the resistive structure from the magnetotelluric data (Lin et al, 2017) and found that the tomography and magnetotelluric results are totally the same. The conversion relationship between density and Vs is from Wang et al (2018). The initial Moho depths are based on the results of receiver function (Wang et al, 2019).…”

Gravity analysis of the offset between crustal structure and topography in the Liupan Shan, northeast Tibetan Plateau

“…To the south of the study area is the Qinling Orogen, whose eastern and western parts have been uplifted by subduction of the North and South China Blocks and lower crustal flow from the Tibetan Plateau, respectively. The Qinling Orogen is relatively complex because it is situated at the conjunction zone of three main tectonic blocks (Wang et al 2018).…”

“…Gravity and GPS data used in this study were obtained from in situ observations conducted in 2014 and 2017 (Wang et al 2018). Normal correction, free-air correction, Bouguer correction, and terrain correction were performed on the adjusted gravity data to obtain complete BGA (Fig.…”