嵩山路家沟花岗岩地球化学特征

Geochemistry of the Lujiagou Trondhjemite Pluton in Songshan

嵩山是前寒武纪地质研究的典型地区,路家沟片麻状奥长花岗岩体分布于嵩山君召乡北路家沟一带。该岩体富Na_2O、贫铁、镁质氧化物,Al_2O_3含量平均为13.78%,显示贫铝特征;重稀土强烈亏损,轻重稀土强烈分异,Eu出现轻微负异常,高Sr含量和高Sr/Y比值,Cr、Yb、Y含量较低,与新生代高硅埃达克岩地球化学特征相似;岩石Nb、Y、Rb、Th、La和Yb之间的关系特征和岛弧火山岩相似。地球化学特征表明路家沟岩体形成于岛弧或俯冲环境,因此推测是由新生的玄武质洋壳俯冲部分熔融而成。

The Lujiagou gneissic trondhjemite pluton is exposed in Junzhao,Songshan,Henan with grayish white color,fine-grained texture,gneissic texture and banded texture.The rock contains 2.96-3.66%Na2O,70.36-75.76%SiO2,12.69-15.52%Al2O3(average of 13.78%<15%)and is poor in Fe,Mg oxides.It is similar to Si-rich Cenozoic adakite withΣREE of 27.02-177.53 ppm,depletion in HREE and enrichment in LREE,weak negative Eu anomaly,high Sr,high Sr/Y ratio,low Cr,Yb,Y.The Nb,Y,Rb,Th contents and La/Yb ratio are similar to those of island arc volcanic rock.These indicate that the Lujiagou trondhjemite pluton was emplaced in subducting oceanic crust setting.