摘要
本文报道了新获得的南秦岭南缘勉略构造带张儿沟新元古代变安山岩锆石U-Pb年代学、主量和微量元素研究成果,并讨论了秦岭板块和扬子板块西北缘新元古代构造演化历程。张儿沟变安山岩LA-ICP-MS锆石U-Pb测年结果为840±5.4 Ma(MSWD=0.44,n=20)和847±5.7Ma(MSWD=0.45,n=19)。张儿沟变安山岩属准铝质钙碱性系列,具富硅(Si_2O=58.42%～63.57%)、富钠(Na_2O/K_2O=2.02～14.94)、富铝(Al_2O_3=16.80%～17.64%)和低镁(Mg O=1.87%～2.11%)的主量元素地球化学特征,强烈富集Sr(541.42×10^(-6)～674.80×10^(-6)),亏损重稀土元素Y(9.25×10^(-6)～10.11×10^(-6))和Yb(1.10×10^(-6)～1.16×10^(-6)),具有较高的Sr/Y值(56.22～67.17),表现出弱的正铕异常(δEu=1.02～1.07),符合Adakite(高锶低钇中酸性岩,亦译埃达克岩)特征,为俯冲洋壳部分熔融的产物,熔融源区残留相可能为含10%～25%石榴子石角闪岩。张儿沟变安山岩是新元古代勉略洋盆北向俯冲阶段的产物,为Rodinia超大陆聚合事件在该地区的岩浆响应。
This paper presents new results on zircon U-Pb dating, trace and major element analyses of Neoproterozoic Zhangergou metamorphic andesitic rocks in the Mianxian—Lüeyang Tectonic Zone of southern margin of South Qinling Orogen, and the Neoproterozoic tectonic evolution in the junction area between the South Qinling Plate and northwestern Yangtze Plate is also discussed. Zircon U Pb dating determined using laser ablation inductively coupled plasma mass spectrometry from Zhangergou metamorphic andesitic rocks samples yielded weighted mean^206Pb/^238U ages of 840 5.4Ma and 847 5.7Ma. The Zhangergou metamorphic andesitic rocks are high silica （Si2O=58.42～63.57）, Na rich （Na2O/K2O=2.02～14.94）, A lrich （Al2O3= 16.80%～17.64%）, Mg poor （MgO=1.87%～2.11%） calc alkaline rocks, and possess the adakite trace element characteristics such as high Sr （541.42×10^-6～674.80×10^-6）, high Sr/Y ratios （56.22～67.17）, positive Eu anomaly （δEu=1.02～1.07）, low Y （9.25×10^-6～10.11×10^-6） and Yb （1.10×10^-6～1.16×10^-6）. The Zhangergou metamorphic andesitic rocks formed by slab melting in subduction zones, and the source residues likely contained 10%～25% garnet—hornblende. Combining the regional tectonic data, we conclude that the Zhangergou metamorphic andesitic rocks are the product of north trend subduction of Neoproterozoic Mianxian—Lüeyang Ocean and the magmatic response of Rodinia supercontinent.
出处
《地质论评》
CAS
CSCD
北大核心
2016年第2期434-450,共17页
Geological Review
基金
中国地质调查局地质调查项目(编号:1212011120161)
国家自然科学基金项目(编号:41472191、41172186、40972136、40572121)
高等学校博士学科点专项科研基金项目(编号:20110205110004)
中央高校基本科研业务专项基金项目(编号:CHD2011TD020、2013G1271092、2013G1271091)的成果~~
关键词
新元古代
变安山岩
张儿沟
勉略构造带
南秦岭南缘
RODINIA
聚合
Neoproterozoic
metamorphic andesitic rocks
Zhangergou
Mianxian--Ltieyang tectonic zone
southern margin of South Qinling
Rodinia
amalgamation.
