SIMS zircon U-Pb geochronology and Sr-Nd isotopes of Ni-Cu-Bearing Mafic-Ultramafic Intrusions in Eastern Tianshan and Beishan in correlation with flood basalts in Tarim Basin (NW China): Constraints on a ca. 280 Ma mantle plume

Abstract

Zircon SIMS U-Pb dating of the Poshi, Hongshishan, Bijiashan, and Huangshan Ni-Cu-bearing and Xiangshan Ni-Cu-Ti-Fe-bearing mafic-ultramafic intrusions in the Eastern Tianshan and Beishan Rift yields a relatively restricted range of 278.6 Ma to 284.0 Ma. The histogram of compiled age data of basalts in the Tarim Basin and mafic-ultramafic intrusions in the Eastern Tianshan and Beishan Rift has a peak of 280 Ma, which probably represents the time of mantle plume activity. The basalts have lower ε~Nd~(t) values in the range of −9.2 ∼ −1.7 and Mg# of \<50, and higher TiO~2~ contents (\>2 wt.%), indicating that they were generated directly from a peripheral zone of the mantle plume by low degree of melting. The mafic-ultramafic intrusions have higher ε~Nd~(t) of −1.3 ∼ 11.2 and Mg# of 33 ∼ 90, and lower TiO~2~ \< 1.8 weight percent, suggesting that their parental magmas were produced from lithospheric mantle source by high degree of melting due to higher temperature of the mantle plume head. A possible mantle plume model beneath lithospheric mantle of the Tarim Basin, Tianshan and Beishan and its spatial framework is suggested.