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藏北羌塘桃形湖地区出露有一套变质基性岩,主要岩石类型有变质超基性岩、变质堆晶辉长岩、变质辉长岩(辉绿岩)、变质玄武岩和斜长花岗岩等,局部可见有残留的堆晶(层状)结构.变质堆晶辉长岩的锆石SHRIMP定年和Hf同位素研究表明其时代为(467±4)Ma,这是目前羌塘地区时代最老、最可靠的岩浆岩年龄.变质堆晶辉长岩锆石176Hf/177Hf比值介于0.282615～0.282657之间,εHf(t)加权平均值为5.02±0.28,反映其岩浆源区为亏损型地幔.变质基性岩地球化学特征与大洋中脊玄武岩类似,它很可能是古洋壳的残片.桃形湖变质基性岩代表羌塘中央隆起地区早古生代蛇绿岩残片.
A series of metamorphic basement rocks are exposed in the Taoxue Lake area of Qiangtang, northern Tibet. The main types of rocks are metamorphic ultrabasic rocks, metamorphic conglomerate gabbro, metamorphic gabbro (diabase), metamorphic basalts and plagiogranite Etc. The zircon SHRIMP dating and Hf isotopic study of the metamorphic retrograde gabbro indicate that the epoch was (467 ± 4) Ma, which is the oldest in the Qiangtang region , And the most reliable age of magmatic rocks.The 176Hf / 177Hf ratios of metamorphic retrograde metamorphic gabbro range from 0.282615 to 0.282657, and the weighted mean value of εHf (t) is 5.02 ± 0.28, indicating that the magmatic source area is a depleted mantle. The metamorphic basement geochemistry is similar to that of the mid-oceanic basalts, and it is likely to be a fragment of the paleo-oceanic crust. The Taoyuan Lake metamorphic basement rocks represent the Paleozoic ophiolite fragments in the central uplift of the Qiangtang area.