Amphibole—Bearing Peridotite Xenoliths from Nushan,Anhui Province：Evidence for Melt Percolation Process in the Upper mantle and Lithospheric uplift

The spinel peridotite xenoliths of Group I in Quaternary basanites from Nushan,Anhui province,can be classified as two suites:a hydrous suite characterized by the ubiquitous occurrence of (Ti-) pargasite and an anhydrous suite.The nineral chemistry reveals that the anhydrous suite and one associated phlogopite-bearing lherzolite are equilibrated under temperature conditions of 1000-1100℃,whereas amplhibole-bearing peridotites display distinct disequilibrum features,indicating partial reequilibration from 1050 to 850℃ and locally down to 750℃. The amplhbole-bearing peridotites were probably the uppermost part of the high temperature anhydrous suite which was modally modifed by fractionating H2O-rich metasomatic agent during regional upwelling.This relatively recent lithospheric uplift event followed an older uplift event recognized from pyroxene unmixing of domains in local equilibrium,as well as the dominant deformation texture in the anhydrous suite.The first thermal disturbance can be linked with the regional extension and widespread basaltic volcanism in Jiangsu-Anhui provinces since Early Tertiary and the formation of the nearby Subei(North Jiangsu) fault-depression basin during the Eocene,while the second event in association with the formation of amphiboles probably indicates the continuation but diminution of upwared mantle flux since Neogene in response to the change in tectonic regime for eastern china.

Amphibole-bearing peridotite xenoliths from Nushan, Anhui Province: Evidence for melt percolation process in the upper mantle and lithospheric uplift

The spinel peridotite xenoliths of Group I in Quaternary basanites from Nushan, Anhui Province, can be classified as two suites: a hydrous suite characterized by the ubiquitous occurrence of (Ti-) pargasite and an anhydrous suite. The mineral chemistry reveals that the anhydrous suite and one associated phlogopite-bearing lherzolite are equilibrated under temperature conditions of 1000–1110°C, whereas amphibole-bearing peridotites display distinct disequilibrium features, indicating partial reequilibration from 1050 to 850°C and locally down to 750°C. The amphibole-bearing peridotites were probably the uppermost part of the high temperature anhydrous suite which was modally modified by fractionating H₂O-rich metasomatic agent during regional upwelling. This relatively recent lithospheric uplift event followed an older uplift event recognized from pyroxene unmixing of domains in local equilibrium, as well as the dominant deformation texture in the anhydrous suite. The first thermal disturbance can be linked with the regional extension and widespread basaltic volcanism in Jiangsu-Anhui provinces since Early Tertiary and the formation of the nearby Subei (North Jiangsu) fault-depression basin during the Eocene, while the second event in association with the formation of amphiboles probably indicates the continuation but diminution of upward mantle flux since Neogene in response to the change in tectonic regime for eastern China. Supported by the Chinese Academy of Sciences and the National Educational Committee.