Geochemical characteristics and geological signifi-cance of Binggounan Formation meta-volcanic rocks on the northern side of Yusupualeketage at the southern edge of the Al-tun Mountains

The Binggounan Formation volcanic rocks on the northern side of Yusupualeketage at the southern edge of the Altun Mountains are a suite of basic volcanic rocks associated with littoral neritic facies terrigenous clastic rocks and carbonate rock. The gneiss rocks are composed mainly of basalt-andesite and andesitic tuff lava. Geochemical analysis shows that the SiO₂ content of the rocks is between 48.28% and 51.98% with an average of 50.31%. The rocks have rich alkal and low titanium. The Rittman index(δ) is 0.33~2.30 and the aluminum saturation index(A/CNK) is 0.45~0.88, suggesting calc-alkaline series.The value of Mg^# is between 40.46 and 56.28, with an average of 50.12. It is shown that the basic volcanic rocks experienced higher crystallization differentiation, suggesting a weaker right-inclined LREE enrichment type. Eu anomaly is not obvious, and δEu is between 0.81 and 1.17. Lithophile elements Rb, Ba, K, Sr and high field strength elements P, Ti, Nb, Hf are depleted, and incompatible elements Th, U are enriched, implying incompatible enrichment type. The trace elements and rare earth elements have the characteristics of intraplate basalt. Ac-cording to the tectonic environment discrimination series diagram and the comprehensive analysis, the basic volcanic rocks were formed in an inner-plate rift environment. The regional plate breakup of the Paleoproterozoic continent occurred from Changcheng period to the early Qingbaikou period, forming basic volcanic rocks. In the late Qingbaikou period, the evolution began to turn to the Rodinia supercontinent squeeze convergence stage.