Geochemical characteristics and zircon U-Pb isotopic ages of island-arc basic igneous complexes from the Tianshui area in West Qinling
Geochemical characteristics and zircon U-Pb isotopic ages of island-arc basic igneous complexes from the Tianshui area in West Qinling
复制标题
DOI：
10.1007/s11707-007-0008-3
复制
发表时间：
2007-03
影响因子：
2.9
通讯作者：
Pei Xianzhi;Li Zuochen;Hu Bo;Liu Huibin;Liang Gaoyang;Ding Saping;Guo Jun-feng
中科院分区：
文献类型：
--
作者：
Pei Xianzhi;Li Zuochen;Hu Bo;Liu Huibin;Liang Gaoyang;Ding Saping;Guo Jun-feng
天水地区管子镇柳水沟中基性变质火成岩杂岩主要由变质长岩、变质长闪长岩和变质闪长岩组成，白花基性变质火成岩杂岩主要由辉石岩、辉长岩（辉长闪长岩）、闪长岩和石英闪长岩组成。它们形成了一个比较完整的岩浆演化系列。中基性火成岩地球化学特征表明其属于拉斑岩套。它们的球粒陨石归一化稀土元素谱图接近平坦，为lree微富集型，原始地幔归一化和morb归一化的微量元素蜘蛛图基本相似；lles Cs、Ba、Sr、Th、U富集，Rb、K富集，hfse Nb、P、Zr、Sm、Ti、Y富集。这些都表现出岩浆演化和遗传特征。微量元素的构造环境判别表明，这些火成岩杂岩形成于岛弧环境。管子镇地区柳水沟中基性变质火成岩的热电离质谱（TIMS）单粒锆石U-Pb年龄为（507.5±3.0）Ma，代表了这些火成岩杂岩的年龄；表明西秦岭北段岛弧型岩浆岩为晚寒武世，同时也揭示了以关子镇蛇绿岩为代表的古海洋盆地俯冲和由此产生的岛弧型岩浆活动可能发生在晚寒武世至早奥陶世。
The Liushuigou intermediate-basic meta-igneous complex at Guanzizhen, Tianshui area, is mainly composed of metagabbro, metagabbro diorite and metadiorite, while the Baihua basic meta-igneous complex consists mainly of pyroxenite, gabbro (gabbro diorite), diorite and quartz diorite. They form a relatively complete comagmatic evolutionary series. The geochemical characteristics of intermediate-basic igneous rocks indicate that they belong to a tholeiite suite. Their chondrite-normalized REE patterns are nearly flat and are LREE-slightly enriched type, and their primitive mantle-normalized and MORB-normalized trace element spider-grams are generally similar; the LILEs Cs, Ba, Sr, Th and U are enriched, while Rb and K and the HFSEs Nb, P, Zr, Sm, Ti and Y are depleted. All these show comagmatic evolutionary and genetic characteristics. The tectonic environment discrimination by trace element reveals that these igneous complexes formed in an island-arc setting. The Thermal Ionization Mass Spectrometry (TIMS) single-grain zircon U-Pb age for the Liushuigou intermediate-basic meta-igneous rocks in the Guanzizhen area is (507.5±3.0) Ma, representing the age of these igneous complexes, which indicates that island-arc-type magmatite rocks in the northern zone of West Qinling are Late Cambrian and also reveals that the timing of subduction of the paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magmatic activity are probably Late Cambrian to Early Ordovician.