Provenance of the Laga Formation at the Nixiong Area of the Western Lhasa Terrane: constraints from geochemistry of clastic rocks

Owing to the lack of Late Paleozoic magmatic rocks in the western segment of Lhasa terrane, it is difficult to understand its Late Paleozoic tectonic evolution in terms of magmatism. Here we report the geochemical characteristics of the clastic rocks from Laga Formation in Nixiong area, in order to reveal its tectonic background and provenance. The contents of main and trace elementcs of the First and Second Members of Laga Formation in Nixiong areas are slightly different. The Second Member of Laga Formation show higher CaO, Na₂O and V, Cr, Ni, Co contents, and light rare earth elements than the Second Member of Laga Formation, indicating their different sedimentary sources. The tectonic settings of the Laga Formation are characterized by passive continental margin and active continental margin, and the Second Member is with more features of active continental margin. The clastic rocks of the Laga Formation were mainly derived from the matural continental source areas, and the source materials were from recycling deposition of the basement rocks and the early Paleozoic sedimentary rocks in the northern margin of Gondwana land. The source rocks of the Second Member of Laga Formation comprised a few acid and basic components, which equated with magmatic activities during Pan-African period and Cambrian in the northern margin of Gondwanaland.