Details

Autor(en) / Beteiligte

• Cao, Yu-ting
• Liu, Liang
• Chen, Dan-ling
• Wang, Chao
• Yang, Wen-qiang
• Kang, Lei
• Zhu, Xiao-hui

Titel

Partial melting during exhumation of Paleozoic retrograde eclogite in North Qaidam, western China

Ist Teil von

• Journal of Asian earth sciences, 2017-10, Vol.148, p.223-240

Ort / Verlag

Elsevier Ltd

Erscheinungsjahr

2017

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• [Display omitted] •Felsic veins are identified in retrograde eclogites in the Lvliangshan unit.•The eclogites yielded eclogite-facies age of 440Ma and granulite-facies age of 420Ma.•422Ma felsic veins formed during HP granulite stage of the retrograde eclogites.•Felsic veins were derived from anatexis of the eclogites at the HP granulite stage.•Dehydration of zoisite and sodic-amphibolite triggered melting of the eclogites. Ultrahigh pressure (UHP) rocks are often overprinted by high pressure (HP) granulite-facies metamorphism during exhumation. Here we investigate retrograde eclogite from the Lvliangshan area in North Qaidam which is associated with abundant felsic veins. The eclogite adjacent to the vein shows conversion to garnet amphibolite. Petrographic, mineralogical, geochemical, geochronological data suggest that the eclogite has been experienced peak eclogite facies metamorphism at c. 440Ma, followed by granulite facies retrogression at c. 420Ma, and amphibolite facies overprinting at <420Ma. The retrograde eclogite has microstructural records for partial melting with elongated plagioclase grains occurring as veinlets along the garnet-ilmenite grain boundaries and interspersed in clinopyroxene. Moreover, highly cuspate, wedge–shaped and triangular plagioclase grains are distributed along the garnet boundaries, and banded felsic veins (Pl+Qz) occur along the boundaries of amphibole in garnet amphibolite. Whole-rock geochemistry suggests that the felsic veins have 438.1–1106ppmSr and 2.87–12.18ppm Y with Sr/Y ratios from 81.98–166.2, exhibit pronounced positive Eu anomaly, and depletion of HREE, resembling those of adakitic rocks. Felsic veins contain zircon grains with an U-Pb age of ∼422Ma, similar to the age of HP granulite–facies metamorphism (420Ma) of retrograde eclogite. Combined with the identical Hf isotope compositions between the granulite–facies zircon grains from the host retrograde eclogite and those from the felsic vein, we infer closed system partial melting during HP granulite facies retrogression of the retrograde eclogite. The tonalitic (high Sr/Y ratio and enrichment of LREE) chemical feature, low Rb/Sr and high Ba/Rb ratios of the felsic veins suggest that zoisite and sodic amphibolite dehydration-melting together account for the formation of felsic veins during exhumation from the eclogite–facies to granulite–facies stages.