广西清湖二长岩稀土元素地球化学

The REE Geochemistry of Qinghu Monzonite,Guangxi

清湖二长岩是燕山早期源于下部地壳的岩浆在中深成条件下冷凝结晶形成的,属碱性系列的中性岩类,其^(87)Sr/^(86)Sr(磷灰石)=0.70472±0.0004,锆石U-Pb同位素年龄为158.4Ma(不一致线下交点年龄),稀土含量284.69(ppm),∑Ce/∑Y=6.44,δEu=0.88。岩石中稀土元素除小部分在岩浆上侵同化围岩时来源于围岩外,主要来自深部(下部地壳,与岩浆同源),稀土元素在岩浆的结晶分异过程中主要以独立稀土矿物及类质同象替代的含稀土矿物两种形式沉淀下来,其中稀土矿物褐帘石及含稀土矿物角闪石、斜长石和磷灰石是岩石中稀土元素的主要载体,它们决定了岩石在以后的风化分解过程中稀土元素的进一步迁移富集。

The Qinghu monzonite was formed by the cooling and crystallization of themagma derived from the lower crust layer. It belongs to the intermediate rocksof the alkaline series, having 87~Sr/86~Sr (apatite) of 0.70472±0.0004, and U-Pb(Zircon) isotope age of 158.4 Ma. Its REE abundance is 284.69 ppm, ∑Ce/∑Y= 6.40, δEu= 0.88. The majority of the REE of the rock body come from the deep-seatedsourse, i. e. the lower crust layer, although a small Preportion from surroundingrocks. As magma was crystallized and differentiated, REE in it were mainlydeposited as REE mineral orthite, and REE-bearing amphibole, Plagioclase and ??apatite, which are main REE carrier in the rocks, and play an important rolein REE immigrating and gathering in the weathering crust during the weathe-ring and decomposition of the rocks.