Geochemical Characters and Geological Implications of Volcanic Rocks from Maoniushan Formation in Amunick Mountain of Northern Qaidam

A large area of volcanic rocks is dispersed in Maoniushan Formation of Amunick area, northern Qaidam basin. In this paper, the rock association and geochemical characters of these volcanic rocks have been studied. The results show that these volcanics mainly consist of medium-acidic volcanic rocks, with columnar joints, belonging to typical continental volcanic rocks.The Rittman indexes of these volcanics vary from 1.45 to 4.54, with great range of ALK content, and their ACNK ratios change from 0.66 to 1.19, showing the geochemical characters of volcanics with two sources (S-type and I-type) and the mixed source evolution. The LREE of these volcanic rocks are enriched, while their HREE are depleted, with obvious U loss. The structural environment of these volcanic rocks belongs to island environment. The Zircon ages is classified into Middle to Late Devonian, showing the uplifting of Amunik Mountain in this period. And then, the marine sedimentary rocks had appeared in this area during Late Devonian to Early Carboniferous, explaining that the Paleo-Tethys Ocean was opened again and the marine sedimentary was began.