Constraints on the evolution of crustal flow beneath Northern Tibet

Abstract

Crustal flow is an important tectonic process active in continent‐continent collisions and which may be significant in the development of convergent plate boundaries. In this study, the results from multidimensional electrical conductivity modeling have been combined with laboratory studies of the rheology of partially molten rocks to characterize the rheological behavior of the middle‐to‐lower crust of both the Songpan‐Ganzi and Kunlun terranes in the northern Tibetan Plateau. Two different methods are adopted to develop constraints on melt fraction, temperature, and crustal flow velocity in the study area. The estimates of these parameters are then used to evaluate whether crustal flow can occur on the northern margin of the Tibetan plateau. In the Songpan‐Ganzi crust, all conditions are satisfied for topography‐driven channel flow to be dominant, with partial melt not being required for flow at temperature above 1000°C. Further north, the Kunlun fault defines the southern boundary of a transition zone between the Tibetan plateau and the Qaidam basin. Constrained by the estimated melt fractions, it is shown that channel injection across the fault requires temperatures close to 900°C. The composition of igneous rocks found at the surface confirm those conditions are met for the southern Kunlun ranges. To the north, the Qaidam basin is characterized by colder crust that may reflect an earlier stage in the channel injection process. In the study area, at least 10% of the eastward directed Tibetan crustal flow could be deflected northward across the Kunlun Fault and injected into the transition zone defining the northern margin of the Tibetan plateau.

Varying Indian crustal front in the southern Tibetan Plateau as revealed by magnetotelluric data

“…Geochemical data from Jiru Cu deposit located in the Gangdese porphyry Cu belt suggest that the post-collisional Miocene porphyry intrusions were generated by partial melting of the subduction-modified lower crust (Yang et al 2016). Also, the results indicate increasing of water content over 4 wt.% with fractional crystallization (Yang et al 2016) that would actively enhance the conductance and corresponding partial melting (Le Pape et al 2015). Studies of porphyry Cu deposits also suggest that potassic magmas are probably related with partial melting of the thickened juvenile mafic lower crust or delaminated lower crust .…”

“…The conductance of the mid-to lower crust north of the YZS corresponds to a bulk resistivity of 1-8 Ωm. Using Archie's Law, previous studies suggest that a bulk resistivity of 10 Ωm require a melt fraction of 4-9%, while 3 Ωm requires a melt fraction of 10-23% (Le Pape et al 2015;Rippe and Unsworth 2010). Meanwhile, the laboratory measurements suggest that a melt fraction of 5-10% reduces the crustal strength by one order of magnitude under partially melting conditions (Rippe and Unsworth 2010;Rosenberg and Handy 2005).…”

Eocene to late Oligocene history of crustal shortening within the Hoh Xil Basin and implications for the uplift history of the northern Tibetan Plateau

“…Duan et al , , ; Polissar et al , ; Miao et al , ; Sun et al , ]. Along with geophysical and petrological data in the northern Tibetan Plateau [ Owens and Zandt , ; Hacker et al , , ; Ding et al , ; Klemperer , ; Karplus et al , ; Jiang et al , ; Le Pape et al , ], our calculations are supportive of a model in which the modern elevation and crustal thickness of the Hoh Xil Basin were attained via ~24% shortening followed by lower crustal flow.…”

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

“…High conductivity anomalies are widely distributed in the middle to lower crust and upper mantle, and there are various causes of these anomalies in different regions (Xiao et al, 2007(Xiao et al, , 2011Pape et al, 2015;Novella et al, 2017). Hence, it is crucial to comprehensively measure the electrical conductivities of minerals and rocks that are distributed in the deep Earth.…”