珲春小西南岔地区白垩纪花岗岩主要有英云闪长岩和花岗闪长岩两种类型。英云闪长岩属于中钾钙碱性系列（Na2 O ／K2 O ＝1．99～2．76），具有高 Al2 O3（15．46％～17．13％）、Sr（559×10－6～731×10－6）、Sr／Y（40～78）、La／Yb（16～21），低 Y（9×10－6～14×10－6）、Yb（0．8×10－6～1．3×10－6）的特征，与埃达克质岩石地球化学特征类似。花岗闪长岩为高钾钙碱性系列，Na2 O／K2 O ＝1．01～1．56，w（Sr）＝312×10－6～410×10－6、w（Yb ）＝1．23×10－6～2．13×10－6、Sr／Y ＝13～32，属正常的高钾钙碱性花岗岩。两类花岗岩的源区均为玄武质下地壳物质，英云闪长质岩浆形成压力较高（＞1．0 GPa），深度大于33 km ，花岗闪长质岩浆形成压力相对较低（0．8～1．0 GPa），岩浆来源深度为26～33 km 。%The Cretaceous granites from Xiaoxinancha in Hunchu area consist predominantly of tonalites and granodiorites .The tonalites belong to sodic calc‐alkaline series (Na2 O/K2 O = 1 .99 2 .76) , and are characterized by high Al2 O3 (15 .46% 17 .13% ) and Sr (559 × 10- 6 731 × 10 - 6 ) ,high Sr/Y (40 78) and La/Yb (16 21) ratios ,but low Y (9 × 10 - 6 14 × 10 - 6 ) and Yb (0 .8 × 10 - 6 1 .3 × 10 - 6 ) , similar to adakites .The granodiorites are high K and calc‐alkaline .Na2 O/K2 O and Sr/Y ratios fall in the ranges of 1 .01 to 1 .56 ,13 to 32 respectively ,Sr and Yb contents are 312 × 10 - 6 to 410 × 10 - 6 , 1 .23 × 10 - 6 to 2 .13 × 10 - 6 respectively ,features of high‐potassium calc‐alkaline I‐type granites .Both tonalites and granodiorites were resulted from partial melting of the basaltic lower crust .The tonalitic magmas were generated under a pressure greater than 1 .0 Gpa and a depth over 33 km ,while the granodioritic magmas were produced under a relatively lower pressure ( 0 .8 1 .0 GPa) and a depth from 26 km to 33 km .
展开▼
