摘要
秦岭-大别造山带中、新生代中酸性火山岩的地球化学研究表明，该区中酸性火山岩是由幔源基性岩浆与壳源物质的混合物经过多种过程（部分熔融、分离结晶等）综合作用形成的。结合野外地质产状和同位素热年代学资料，作者认为研究区中、新生代火山岩产出于拉张的构造环境中。
A geochemical study, on major, trace and earth elements, of post-collisional intermediate and acid volcanic rocks from the Qinling-Dabie orogen was carried out.SiO2 contents of these volcanic rocks range from 55% to 79%; MgO contents are less than 4%; and Na2O + K2O contents are larger than 6%. Major element oxides versus SiO2 diagram shows an overall negative covariance of Al2O3 and CaO with SiO2. The other oxides are more scattered. In the chondrite-normalized abundance diagram, the acid volcanic rocks have negative slopes with large relative depletions of Nb, P, Ti comparing with the similar compatible elements. As for the intermediate volcanic rocks,no any relative depletion of Nb was found and the relative depletions of P and Ti are smaller than those of the acid volcanic rocks. In the chondrites-normalized REE diagram, trachyandesites, andesites, dacites and trachydacites show parallel patterns and small Eu anomalies. However, rhyolites have irregular patterns and show remarkable Eu anomalies. The origin of the post-collision intermediate and acid volcanic rocks is analyzed based on its geochemical characteristics. Intermediate and acid volcanic rocks in this area were derived from the mixture of the basic magma and crustal material,which experienced multi-proccess evolution. Based on the geochemical characteristics of these volcanic rocks, the thermal chronological data and the geological evidence,the tectonic setting during the formation of these volcanic rocks is constrained. It is believed that during the volcanic eruption, the structural setting in the Qinling-Dabie orogenic belt transferred from compressive to extensive regime.
出处
《地球化学》
CAS
CSCD
北大核心
1998年第6期537-548,共12页
Geochimica
基金
国家自然科学基金!49290102
地质矿产部重大基础项目!8502206
关键词
火山岩
地球化学
构造背景
秦岭-大别
造山带
volcanic rocks, geochemistry, structural setting, Qinling-Dabie orogen
