柴北缘阿木尼克山牦牛山组火山岩地球化学特征及其地质意义

柴北缘阿木尼克地区分布有大面积的牦牛山组火山岩,通过对火山岩岩石组合、地球化学、锆石测年等研究。研究结果表明该区岩性组合以中-酸性火山岩为主，发育柱状节理，为典型陆相火山岩。里特曼指数（δ）为1.45~4.54，全碱（ALK）含量变化范围较大，铝饱和指数为0.66~1.19，具2种来源地球化学特征的火山岩（S和I型），显示混源演化，轻稀土富集，重稀土亏损，铀亏损明显。构造环境均显示为岛弧，锆石年龄为中-晚泥盆世，表明阿木尼克山一带在该时期主体处于隆升状态，而到了晚泥盆世-早石炭世时期则出现了海相沉积岩，说明古特提斯洋重新打开，拉开了该区海相沉积帷幕。

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.