鲁西地区角闪石岩地球化学、矿物学特征及其地质意义

Geochemical and Mineralogical Characteristics of Hornblende in Western Shandong and Their Geological Significance

基性-超基性岩脉群通常形成于伸展构造背景,是示踪地幔源特征以及大陆和超大陆破裂的重要标志。鲁西地区角闪石岩为研究古元古代岩浆源和构造演化提供了一个窗口。本文对鲁西地区角闪石岩进行了岩相学、全岩地球化学及角闪石、黑云母电子探针原位分析。角闪石岩具板内构造环境,来自富集地幔。通过角闪石、黑云母成因分析,均具有幔源成因,角闪石结晶温度为702~781℃;结晶压力为29.8~228.8MPa,结晶深度1~7.5km,结晶时氧逸度变化范围在NNO+2.68到NNO+3.35之间。结合本次获得角闪石岩磷灰石U-Pb年龄为(1817±35) Ma,认为鲁西地区(1817±35) Ma处于板内拉伸环境,存在幔源岩浆上侵,已进入大陆裂解阶段。

Dike groups are formed under extensional background and are an important indicator for tracking mantle source characteristics, and continental and supercontinental rupture. Hornblende rocks in western Shandong enable the evaluation of Paleoproterozoic magma source and tectonic evolution. In the present study, petrographic,whole-rock geochemical, and in situ analyses of amphibole and biotite in the western Shandong area were carried out. Hornblende rocks with intraplate tectonic setting from enriched mantle were employed. According to an analysis of the origin of hornblende and biotite, both were of mantle origin. The crystallization temperature of hornblende was 702~781 ℃. Further, hornblende had a crystallization pressure of 29.8~228.8 MPa,crystallization depth of approximately 1~7.5 km, and its oxygen fugacity varied from NNO+2.68 to NNO+3.35 during crystallization. As the U-Pb age of hornblende apatite was(1817±35) Ma,(1817±35) Ma in the western Shandong area was considered to be in the in-plate tensile environment, where mantle derived magma transgression occurs, and the stage of continental cracking is entered.