Crustal contamination and magmatic evolution of the Bijiashan basic–ultrabasic intrusion belt in the Beishan Terrane, northeastern Tarim Craton (NW China)

• Published in: Geological journal (Chichester, England) Vol. 53; no. S2; pp. 30 - 43
• Main Authors: Xia, Zhaode, Du, Wei, Xia, Mingzhe, Jiang, Changyi, Yang, G.
• Format: Journal Article
• Language: English
• Published: Liverpool Wiley Subscription Services, Inc 01.07.2018
• Subjects: Aluminum oxide; basic–ultrabasic rocks; Composition; Contamination; Cratons; crustal contamination; Crystallization; Dunite; Earth; Evolution; Field strength; Fractional crystallization; Gabbro; Intrusion; Lava; Magma; magma source; magmatic evolution; Magnesium oxide; Niobium; Olivine; parental magma; Plagioclase; Ratios; Rock; Rocks; Rubidium; Strontium 87; Strontium isotopes; Tantalum; Trace elements; Uranium; Zirconium
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.3219

The Bijiashan intrusion belt, one of the basic–ultrabasic intrusion belts in the Beishan Terrane, northeastern Tarim Craton, is composed of the Hongshishan, Hongshishanxi, Xuanwoling, Bijiashandong, and Bijiashan intrusions. These intrusions are mainly composed of dunite, troctolite, olivine gabbro, and gabbro. Magma evolution of the intrusions was strongly controlled by fractional crystallization, and the crystallization sequence was mainly olivine → plagioclase → pyroxene. This is evidenced by whole‐rock MgO contents that are positively correlated with TFe2O3 and negatively correlated with Al2O3, CaO, and Na2O and an increase in total rare‐earth element and trace elements contents from ultrabasic to basic rocks. Most of the basic–ultrabasic rocks are enriched in large ion lithophile elements (Cs, Rb, Sr, and U) and depleted of high field strength elements (Zr, Hf, Nb, Ta, and Ti). The variable and relatively low Ce/Pb (0.17–7.3) and Nb/U (0.13–10.1) ratios, variable Th/Yb (0.02–4.1) ratio, initial 87Sr/86Sr ratios (0.7033 to 0.7094) and εNd (t) (7.54 to −4.25), suggest less than 6% crustal contamination. Based on the maximum Fo value of olivine (Fo90), whole‐rock average composition and olivine–liquid compositional relationships, the parental magma is of high‐Mg basaltic magma containing 13.4 wt.% MgO. According to rare‐earth element contents and Sr–Nd isotopic compositions, the parental magma was originated from partial melting of depleted sub‐continental lithospheric mantle.