本溪地区BIF中玄武质围岩的高场强元素特征

辽宁本溪地区条带状铁矿(BIF)与其玄武质火山围岩之间的时空关联非常密切.对于玄武质火山围岩高场强元素(HFSE)的研究表明:wNb/wTa比值(7.00~19.93)表现出明显的分异,而wZr/wHf比值(33.46~38.28)则变化不大;从弓长岭到南芬、歪头山样品的wNb/wTa比值变化具有明显的循序性.这种高场强元素的迁移和分异特征反映出俯冲作用与盆地演化之间的关联.研究区玄武质火山围岩(wNb/wYb)N比值大于1(1.21~18.45,平均2.72),这进一步表明,其形成的构造背景为陆内弧后盆地提供了有利于BIF形成的条件.

HFSE Characteristics of Basaltic Volcanic Wall Rocks Around BIFs in Benxi Area

BIFs have spatial and temporal association with their basaltic volcanic wall rocks in Benxi area of Liaoning Province. Through an analysis on the HFSE (high field-strength element)characteristics of basaltic volcanic wall rocks around BIFs， it was found that their w_○Nb/w_○Ta ratios (7.00~19.93) were remarkably fractionated， but the fractionation of w_○Zr/w_○Hf ratios (33.46~38.28) was not so obvious. In addition， the fractionation of w_○Nb/w_○Ta ratios had regional tendency from Gongchangling to Nanfen and Waitoushan. These migration and fractionation characteristics of HFSE showed a connection between basin evolution and subduction process. Their (w_○Nb/w_○Yb)_N ratios (1.21~18.45， average 2.72) were greater than 1， further suggesting that the tectonic setting for BIFs in the studied area was an intra-continental back arc basin.