Discovery of ultrahigh-pressure magnesite-bearing garnet lher- zolite (>3.8 GPa) in the Altyn Tagh, Northwest China

Exsolution microstructures in ultrahigh-pressure rocks: Progress, controversies and challenges

“…The reconstructed precursor supersilicic garnet composition suggested for the first time subduction and exhumation of continental crust rocks to depths greater than 200 km [9] . Since then, similar exsolution microstructures were reported from various UHP terraines one after the other including Erzgebirge massif [44] of German and the northern margin of Caidam [17] and Altyn [45][46][47] of western China. Dobrzhinetskaya et al [48] successfully simulated the exsolution of clinopyroxene from supersilicic garnet by a series of decompression experiments (pressure decreasing to 12 GPa from 14 GPa at constant temperature of 1400℃), demonstrating that the exsolved clinopyroxene "blebs" mainly occur at the sites of triple conjunction of polycrystalline aggregates of supersilicic garnet.…”

Coesite in eclogite from the North Qaidam Mountains and its implications

“…It has been correlated to the south Altyn Tagh HP/UHP metamorphic terrane, and constrains a 400 km offset for the Altyn Tagh fault. Therefore, South Altyn-North Qaidam was considered as a single HP-UHP metamorphic belt truncated by a large strike-slip fault, similar to the case of the Dabie-Sulu HP-UHP metamorphic zone which was truncated by the sinistral Tanlu strike-slip fault in eastern China, and split into the Dabie and Sulu regions [14][15][16][17][18][19][20][21] . However, in contrast to Dabie-Sulu in eastern China, where UHP metamorphic evidence has been commonly recognized in different rock types, evidence of UHP metamorphism is relatively rare in the north Qaidam (NQD) and south Altyn Tagh (SAT) [11,22,23] .…”

Bashikaogong-Shimierbulake granitic complex, north Altun, NW China: Geochemistry and zircon SHRIMP ages

“…Zircon SHRIMP U-Pb dating shows that the quartz diorite has a bigger age than those of other granites, which is 481.6±5.6 Ma for quartz diorite, 437.0±3.0 Ma-433.1±3.4 Ma for grey granite and 443±11 Ma-434.6±1.6 Ma for pink granite, respectively. Combined with regional geology, we think that the quartz diorite formed in tectonic environment related to oceanic crust subduction and the granites in post-collision.The basement of Milanhe-Jinyanshan in the North Altun terrain consists of a suit of Precambrian metamorphic rocks including gneiss, schist and highpressure metapelite [1] . A number of mafic and ultramafic rocks include basalt and pillow lavas, as well as siliceous rocks (tuff and granite) [2] , which is a subduction-collision complex belt characterized by ophiolite, abyssal and bathyal clastic rocks, carbonate rocks and metamorphic rocks.…”

“…It has been suggested to result from subduction of a continental crust to 80 km deep and later exhumation to near surface [3,4] . The basic rocks are mainly transitional MORB-type basalts with minor OIB-type basalts formed at about 508.13±41Ma-524.14±44Ma (Sm-Nd isochron age) [1,2,5] . The granites intruded into the gneissic wall rocks either as relatively large plutons or small-scale veins.…”

“…The basement of Milanhe-Jinyanshan in the North Altun terrain consists of a suit of Precambrian metamorphic rocks including gneiss, schist and highpressure metapelite [1] . A number of mafic and ultramafic rocks include basalt and pillow lavas, as well as siliceous rocks (tuff and granite) [2] , which is a subduction-collision complex belt characterized by ophiolite, abyssal and bathyal clastic rocks, carbonate rocks and metamorphic rocks.…”