摘要
广东从化恶鸡脑碱性正长岩岩体是广东乃至华南地区唯一已知的中生代含副长石及碱性暗色矿物的碱性正长岩岩体。岩石含有霞石、白榴石及岩浆成因的方钠石。碱性正长岩体侵入到燕山期第三期的佛冈岩体之中，岩体侵位年龄为127.5Ma(角闪石Ar-Ar法)。岩体富大离子亲石元素，贫Sr和Ba,具有明显的铕负异常，富Nb和Zr等高场强元素。εNd(t)为近于零的负值（－0.66～－1.6）,模式年龄tDM较小（0.91～0.99Ga）,钕同位素组成显示出其成岩物质主要源于富集的上地幔源区。造山后准铝质A型花岗岩[(158±17)Ma]-非造山A型花岗岩(～132Ma)-碱性正长岩(127.5Ma)的构造岩浆组合，是侏罗纪中国东南部由挤压造山向拉张伸展转变的产物,表明华南地区岩石圈拉张作用应始于晚侏罗世。具有铕负异常的碱性正长岩的产出,标志着早白垩世造山作用的结束、山根消失及大规模拉张构造事件的开始。
The Ejinao alkali syenite, Conghua, Guangdong Province, is the only later Mesozoic alkali syenite known in SE China which contains feldspathoid minerals. The alkali syenite contains nepheline, leucite and magmatic sodalite which forming eutectic texture with potash feldspar. The characteristics of trace and rare earth elements of the Ejinao alkali syenite are comparable to those of the Fugang biotite granite, which implies a probable successive petrogenetic evolution. The alkali syenite is enriched in large ion lithophile elements, high field strength elements (i.e., Nb, Zr), and depleted in Sr and Ba. The syenite shows significant negative Eu anomalies. Regarding its Nd isotopic composition, ε Nd(t) ranges from － 0.66 to － 1.6, and t2DM = 0.91～0.99 Ga, indicating the alkali syenite should derive mainly from fertilized upper mantle sources and was contaminated by the crustal material (Fugang granites ?). The tectonic- magmatic association of the Fugang post- organic metaluminous A type granite, Nankunshan anorogenic A type granite, alkali syenite and alkali basalt association emplaced from Jurassic Period to Cretaceous Period within the Enping- Xinfeng fault belt was recognized. This association indicates that the orogenic belt collapsed in later Jurassic Period and the continental root vanished and large- scale extension started from early Cretaceous Period.
出处
《地球化学》
CAS
CSCD
北大核心
2000年第5期462-468,共7页
Geochimica
基金
广东省自然科学基金!(950685)
关键词
微量元素
碱性正长岩
地球动力学
广东
地球化学
trace element
Sr- Nd isotope
alkali syenite
geodynamics
Guangdong Province
