Petrogenesis of Permian Mafic Dikes in Beishan area, Xinjiang: Constraints from Geochemistry

Mafic dikes widely developed in Beishan area of Xinjiang, northeast of Tarim are closely related to cotemporary mafic - ultramafic intrusive bodies. The Permian mafic dikes occur in the Cantoushan, Bijiashan, Baidiwa-Yunihe and other places in Beishan area, Xinjiang. The diabase is an iron mafic rock with SiO2 content ranging from 50.01% to 53.90% and m/f (m/f=(Mg2++Ni2+)/(Fe2++Fe3++Mn2+)) ranging from 1.47 to 1.60. The rocks belong to calc-alkaline series, relatively enriched in LREE and large ion lithophile elements, εNd(t) is +5.5~+6.7 and (87Sr/86Sr)i is 0.704 4~0.704 8, shows the affinity of depleted mantle source metasomatized by fluid. The comprehensive study suggests that the Permian mafic dykes in the Beishan area of Xinjiang were formed in a continental rift environment and were formed by a high degree of partial melting ( 15 %~20 % ) of spinel lherzolite.