甘肃白银厂矿田早—中寒武世火山岩形成的构造环境

甘肃白银厂矿田早—中寒武世火山岩形成的构造环境

王金荣1, 郭原生1, 翟新伟1, 李双文1, 孟桂生2, 杨永钧2

1. 兰州大学资源环境学院地质系，兰州730000; 2. 白银公司小铁山矿，白银730900

收稿日期:2003-03-20 修回日期:2003-03-20 出版日期:2003-03-20 发布日期:2003-03-20

Tectonic Setting for Formation of the Early-Middle Cambrian Volcanic Rocks from Baiyin Mining Field，Gansu Province

WANG Jin-rong1, GUO Yuan-sheng1, ZHAI Xin-wei1, LI Shuang-wen1, MENG Gui-sheng2, YANG Yong-jun2

1. Department of Geology, Resource and Environmental School of Lanzhou University, Lanzhou 730000, China; 2. Xiaotieshan Mine, Baiyin Nonferrous Metal Company, Baiyin 730900, China

Received:2003-03-20 Revised:2003-03-20 Online:2003-03-20 Published:2003-03-20

摘要/Abstract

摘要： 白银厂矿田早－中寒武世火山岩主要由钙碱性玄武岩和流纹岩及少量的安山岩组成，被认为是大陆裂谷环境下的产物。本文的地球化学分析结果显示：玄武岩具有低Ti,Nb和Ta负异常、富集LREE，相对亏损HFSE，Th/Ta比值高（介于9－15），La/Nb>1.4，低Ni,Th/La为0.32-0.56；低Zr/Nb(<16),(^87Sr/^86Sr)i为0．704－0．707，εNd(t)=-6.46,δEu≈1的地球化学特点；流纹岩同样具有低Ti,Nb和Ta负异常，Th/Ta为6－12，低Ti/Zr比值（介于6.1-53)之间；稀土元素配分为MREE负异常，δEu为0.5-1.1,(^87Sr/^86Sr)i为0．7026－0．7048，εNd(t)为＋5.60-+6.14。综合两类岩石的地球化学特征，可以推测它们是陆缘弧岩浆作用的产物，但并非同源岩浆演化的结果。玄武岩源于富集的岩石圈地幔，在岩浆上升过程中发生明显的陆壳混染作用，而流纹岩应为镁铁质下地壳部分熔融与地幔物质混合作用的产物。

Abstract: The early-middle Cambrian volcanic rocks from Baiyin mining field are composed mainly of calc-alkaline basalts，rhyolites and minor andesites． They were considered to be resulted from magmatism of continental rift．The results of the geochemial characteristics show that，compared with oceanic ridge basalt (MORB)，the basalts of study area are characterized by low Ti and Ni(Ni<25 at Mg’=40)，obviously negative anomaly of Nb-Ta，enrichment of LREE。re1ative depletion of HFSE，high ratios of Th／Ta(9～15)，Th／La(0.32-0.56) and La／Nb(>1.4)，highly variable range of Ce／Zr，La／Zr and Nb／Zr，and with low Zr／Nb ratio(<16)．(87Sr／86Sr)i=0.704～0.707， Nd(t)= -6.46 and δEu≈ 1.0．However，the rhyolitic rocks have (87Sr／86 Sr)i=0.7026～0.7048，εNd(t )=+5.60～ +6.14，δEu = 0.5～ 1.1，Th／Ta =6～12 and Ti／Zr 6.1～53．Their REE distribution patterns have a negative anomaly of MREE． indicating the presence of amphibole as a residual phase in the mafic lower crust(pre－existing island arc basalts)． According to the geochemistry of the volcanic rocks，it can be inferred that the basalts and rhyolites were resulted from the ma gmatism in normal continental margin arc， but with different sources． The basalts stemmed from enriched sub-continental lithospheric mantleand the mantle-derived magma was strongly contaminated by continental crust． However, the rhyolitic rocks were resulted from mixing of mafic lower crust generated by partial melting of depleted mantle wedge and subduction-related mantle-derived underplating magmas at the same tectonic episode

王金荣, 郭原生, 翟新伟, 李双文, 孟桂生, 杨永钧. 甘肃白银厂矿田早—中寒武世火山岩形成的构造环境[J]. J4.

WANG Jin-rong1, GUO Yuan-sheng1, ZHAI Xin-wei1, LI Shuang-wen1, MENG Gui-sheng2, YANG Yong-jun2. Tectonic Setting for Formation of the Early-Middle Cambrian Volcanic Rocks from Baiyin Mining Field，Gansu Province[J]. J4.