浙西新路盆地晚白垩世钾玄岩的厘定及其地质意义  

Chronology and Geochemical Characteristics of the Diabase in Xinlu Basin of Western Zhejiang and Their Significance

作　　者：王正其[1] 李子颖[2] 范洪海 汤江伟 

机构地区：[1]东华理工大学放射性地质与勘探技术国防重点学科实验室,江西抚州344000 [2]核工业北京地质研究院,北京100029 [3]浙江省核工业269大队,浙江金华321000

出　　处：《地球学报》2013年第2期139-153,共15页Acta Geoscientica Sinica

基　　金：国家自然科学基金项目(编号:41040019)资助

摘　　要：对浙西新路火山盆地发育的辉绿岩进行了激光显微探针40Ar-39Ar定年和系统的岩石地球化学特征研究。研究表明,新路盆地辉绿岩成岩时代为(93±3)Ma,属晚白垩世产物;岩石中辉石有单斜辉石和斜方辉石两个种属,斜长石为拉长石;SiO2含量介于44.00%～50.09%之间,具有富碱(平均为5.15%)、高钾(K2O/Na2O平均为1.08)、低TiO2含量(平均为1.15%)等特征;岩石具有原生岩浆特点,显示典型的钾玄岩特征。钾玄岩富集LREE、大离子亲石元素和强不相容元素,无Eu亏损;锶初始值(Isr)介于0.70707～0.70870之间,(143Nd/144Nd)i介于0.512338～0.512407之间;Δ7/4Pb为6.0～9.2、Δ8/4Pb为48.5～68.0、Sr为70.73～87.04,均表现出富集地幔特征。认为新路盆地钾玄岩的厘定对该区域岩石圈与构造岩浆演化的深入研究具有重要意义;钾玄岩形成与造山带后碰撞期的热点活动相关;钾玄岩侵位年龄基本限定了新路地区岩石圈大规模减薄的时限;推测热点活动导致岩石圈减薄的动力学演化过程及其壳幔作用源区可能对火山岩型铀成矿起着重要的制约作用。The laser microprobe 40Ar-39Ar dating and detailed study of petrogeochemical characteristics of the diabase developed in Xinlu volcanic basin of western Zhejiang were carried out. The results indicate that the diabase was formed in Late Cretaceous with an ~rge of （93_＋3） Ma. The diabase contains two kinds of pyroxenes （clinopyroxene and orthopyroxene）, the plagioclase is labradorite, and the content of SiO2 is between 44.00% and 50.09%, characterized by rich alkali, （5.15% on average）, high K （K20/Na20 1.08）, and low Ti （TiO2 1.15%）. Its petrological and geochemical characteristics show typical shoshonite. The shoshonite is enriched in LREE, LILE and incompatible elements, without Eu depletion, （875r/86Sr）i and （143Ndlla4Nd）i are in the ranges of 0.70707 to 0.70870 and 0.512338 to 0.512407 respectively, A7/4Pb=6.0~9.2, A8/4Pb=48.5~68.0, and ASr=70.73~87.04, showing relatively enriched mantle signatures. It is concluded that the shoshonite in Xinlu basin is the product of lithospheric thinning combined with hotspot activity in the post-collision period of the orogenic zone. The age of shoshonite fundamentally restricts the time limit of the large-scale lithospheric thinning in Xinlu area, and suggests that dynamic processes of lithospheric thinning was affected by hotspot and the sources of crust-mantle interaction migtht have played an important role in controlling volcanics-type uranium mineralization.

关 键 词：钾玄岩 40Ar-39Ar定年 岩石地球化学 岩石圈减薄 新路火山盆地 

分 类 号：P588.136[天文地球—岩石学] P597.2[天文地球—地质学]