Geochemical and Nd-Sr-Pb isotopic composition of Mesozoic volcanic rocks in the Songliao basin, NE China
Geochemical and Nd-Sr-Pb isotopic composition of Mesozoic volcanic rocks in the Songliao basin, NE China
复制标题
DOI：
10.2343/geochemj.40.149
复制
发表时间：
2006-04
影响因子：
0.8
通讯作者：
P. Wang;Fukun Chen;Shumin Chen;W. Siebel;M. Satır
中科院分区：
文献类型：
--
作者：
P. Wang;Fukun Chen;Shumin Chen;W. Siebel;M. Satır
松辽盆地中生界火山岩是盆地充填物的主要组成部分，是重要的油气储集岩。然而，由于缺乏足够的化学和同位素数据，对这些火山岩的成因及其构造背景知之甚少。这些火山岩覆盖了从玄武粗安岩到高硅流纹岩的广泛成分谱。可分为上侏罗统火石岭组（157 - 146 Ma）和下白垩统营城组（136 - 113 Ma），前者以深灰色安山岩为主，后者以淡黄色流纹岩为主。在成分上，这些岩石是过铝质到变铝质，高钾到中钾，钙碱性。它们富含大离子亲石元素和轻稀土元素，亏损高场强和重稀土元素，普遍表现出Nb、Ti和P的负异常。这些火山岩的初始87 Sr/ 86 Sr比值和初始eNd值分别为0.7034 ~ 0.7106和-3.4 ~5.3。δ 18 O值为3.2‰ ~ 14.8‰。初始206 Pb/ 204 Pb和207 Pb/ 204 Pb比值的范围分别为17.65至18.22和15.52至15.57。Nd和Sr同位素组成特征可能表明富集的类MORB物质与地壳成分的混合。侏罗系和白垩系火山岩的原生岩浆均来源于交代富集的类MORB源，但白垩系流纹岩普遍表现为地壳同化，表现为高的初始87 Sr/ 86 Sr比值和低的初始eNd值。松辽盆地火山岩的形成是与蒙古-鄂霍次克缝合带碰撞后的背景有关，还是与西太平洋板块俯冲有关，还有待讨论。
Mesozoic volcanic rocks exposed in the Songliao basin form a major part of the basin fill and are the important petroleum reservoir rocks. Petrogenesis of these volcanic rocks and their tectonic setting, however, are poorly understood due to lack of sufficient chemical and isotopic data. These volcanic rocks cover a wide compositional spectrum ranging from basaltic trachyandesite to high-silica rhyolite. They can be divided into two formations, the upper Jurassic Huoshiling formation (157‐146 Ma) with dominant dark gray andesite and the lower Cretaceous Yingcheng formation (136‐113 Ma) with dominant yellowish rhyolite. Compositionally, these rocks are peraluminous to metaluminous, high-K to medium-K, calc-alkaline. They are enriched in large-ion lithophile and light rare earth elements, depleted in high field strength and heavy rare earth elements, and commonly display negative anomalies of Nb, Ti and P. Initial 87 Sr/ 86 Sr ratios and initial eNd-values of these volcanic rocks range from 0.7034 to 0.7106 and from ‐3.4 to 5.3, respectively, and their δ 18 O values vary from 3.2‰ to 14.8‰. Initial 206 Pb/ 204 Pb and 207 Pb/ 204 Pb ratios have ranges of 17.65 to 18.22 and 15.52 to 15.57, respectively. The characteristic in Nd and Sr isotopic composition probably indicates a mixing of enriched MORB-like material and crustal component. Primary magmas for both the Jurassic and Cretaceous volcanic rocks could be derived from metasomatized enriched MORB-like sources, but the Cretaceous rhyolites commonly show crustal assimilation indicated by high initial 87 Sr/ 86 Sr ratios and low initial e Nd values. Whether the volcanic rocks in the Songliao basin formed related either to the post-collisional setting of the Mongolia-Okhotsk suture or the subduction of the western Pacific plate remains to be discussed.