New geological evidence of crustal thickening in the Gangdese block prior to the Indo-Asian collision

Active construction of southernmost Tibet revealed by deep seismic imaging

Southernmost Tibet exhibits an anomalously twice the normal thickness of average continental crust. There is no available theory to explain and the driving mechanism remains uncertain. Here, we interpret a north-striking, 180 km-long deep seismic reflection profile traversing the southern Lhasa terrane (SLT) to the central Lhasa terrane (CLT). In addition to reflections showing subducting Indian crust, our results reveal lateral heterogeneity between the SLT and CLT, where north-dipping reflections beneath the CLT outline a tilted crystalline basement, while the non-reflective domain beneath the SLT represents homogeneous juvenile crust. Our integrated analysis leads to models calling upon episodic magmatism onto the southern margin of the basement to result in progressive construction of the SLT. We hypothesize that this crustal thickening via crustal-scale magma accretion contributed to surface uplift of the southern margin of the Tibetan plateau and leading to the development of the vast internal drainage system of Tibet.

Mechanism driving continental growth on modern Earth has long been debated. By interpreting the long deep seismic reflection data across the ongoing India-Eurasia collision zone, the authors report crustal-scale magma accretion onto the south of central Lhasa terrane produced net continental growth.

Early Cretaceous Gangdese retroarc foreland basin evolution in the Selin Co basin, central Tibet: evidence from sedimentology and detrital zircon geochronology

The Selin Co basin in the northern Lhasa terrane includes more than 3000 m of upward coarsening Lower Cretaceous strata, and the sedimentary sequence from the flysch to the molasse indicates the evolution of a foreland basin. Petrographic analysis shows that sandstones are rich in volcanic and sedimentary lithics and most of them fall into recycled orogen and magmatic arc.

Uranium–lead (U–Pb) ages were determined for 435 detrital zircons from the Lower Cretaceous strata in the Selin Co basin. Relative probability of detrital zircon ages shows the Eshaerbu Formation was rich in zircon grains with the age of 125–140 and 160–180 Ma, and the Duoni Formation was dominated by one main age cluster of 125–150 Ma. Analysis of the potential provenances suggests the Early Cretaceous zircon grains were primarily derived from the Gangdese magmatic arc to the south. The youngest zircon ages in the lowermost exposure of the Eshaerbru Formation are c. 130 Ma, providing a maximum depositional age of sediments in the Selin Co basin.

Collectively, our studies, together with previously documented Cretaceous thrusting in the Lhasa terrane, suggest the Lower Cretaceous Selin Co basin was deposited in a retroarc foreland basin. From 145–90 Ma, a retroarc foreland basin was presumed to develop in the Lhasa terrane, migrating from the south to the north. Crustal thickening, likely associated with the evolution of the retroarc foreland basin, was speculated to start in the Early Cretaceous in the Lhasa terrane.

Synthesis of a series of 4-pyridyl-1,2,4-triazole-containing cadmium(ii) luminescent complexes

Using two 4-substitued triazole ligands, 4-(pyrid-2-yl)-1,2,4-triazole (L(1)) and 4-(pyrid-3-yl)-1,2,4-triazole (L(2)), a series of novel triazole-cadmium(II) complexes varying from zero- to three-dimensional have been prepared and their crystal structures determined via single-crystal X-ray diffraction. [Cd(2)(micro(2)-L(1))(3)(L(1))(2)(NO(3))(mu(2)-NO(3))(H(2)O)(2)](NO(3))(2).1.75H(2)O (1) is a binuclear complex containing bidendate, monodedate and free nitrate anions. When the bridging anions SCN(-) and dca (dca = N(CN)(2)(-)) were added to the reaction system of 1, one-dimensional (1D) [Cd(L(1))(2)(NCS)(2)](n) (2) and two-dimensional (2D) [Cd(L(1))(2)(dca)(2)](n) (3) were isolated, respectively. When L(2) instead of L(1) was used, [Cd(L(2))(2)(NCS)(2)(H(2)O)(2)] (4) and 1D [Cd(L(2))(2)(dca)(2)](n) (5) were obtained. When the ratio of Cd to L(2) was changed from 1:2 to 1:1 in the reaction system of 5, three-dimensional (3D) {[Cd(3)(micro(2)-L(2))(3)(dca)(6)].0.75H(2)O}(n) (6) with 1D microporous channels along the a direction was isolated. Further investigations on other Cd(ii) salts and the L(2) ligand in a Cd to L(2) ratio of 1:1, an unexpected complex [Cd(mu(2)-L(2))(mu(3)-SO(4))(H(2)O)](n) (7) with a 3D open framework was obtained. All of the complexes exhibit strong blue fluorescence emission bands in the solid state at ambient temperature, of which the excitation and emission maxima are red-shifted to longer wavelength as compared to those in water. Powder X-ray diffraction and thermal studies were used to investigate the bulk nature of the 3D coordination polymers 6 and 7.