摘要
为确定云南省个旧地区晚中生代大规模岩浆活动过程中基性端元的时限、地幔源区特点及大地构造环境，选取贾沙辉长．二长岩体为对象进行年代学和地球化学研究。贾沙辉长．二长岩体位于个旧西区，岩性主要为辉长岩和二长岩。锆石U．Pb同位素测年结果表明，岩石侵位时代为（84．0＋0．6）Ma，属于晚白垩世，与个旧地区花岗岩、碱性岩和煌斑岩形成年代范围一致（76～85Ma）。贾沙岩体的辉长岩和二长岩Si02为47．3％～60．O％，K20＋Na20为7．31％～10．1％。稀土含量较高，轻稀土富集重稀土亏损，Eu异常不明显。相对于原始地幔，贾沙岩体富集轻稀土和大离子亲石元素Rb、K、Pb，亏损高场强元素Nb、Ta、Ti和P。地球化学研究显示贾沙岩体母岩浆起源于与俯冲有关的交代地幔，由石榴子石二辉橄榄岩经历了较低程度的（〈5％）部分熔融形成。原始岩浆在就位过程中经历了广泛的地壳混染和橄榄石、辉石的分离结晶作用。二长岩由辉长岩浆结晶分异作用形成。研究显示，贾沙辉长．二长岩体是晚白垩世滇东南．桂西地区大规模岩浆活动的产物，表明这些岩浆岩形成于统一的岩石圈伸展的动力学背景下。
The Jiasha intrusion, located in the westem Gejiu district, consist of gabbros and monzonites. We conducted geochronological and geochemical studies to understand the timing, mantle source and tectonic environment of the Jiasha intrusion, a basic end-member of the late-Mesozoic magma activities in the Gejiu area. These rocks have zircon U-Pb ages of-84.0 Ma, synchronous with granitic, alkaline and lamprophyric rocks and Sn mineralization in the Gejiu area （76.0-85.0 Ma）. Both gabbros and monzonites have variable SiO2 （47.3%-60.0%） and K20＋Na20 （7.31%-10.12%）. They have high REE contents, and display LREE-enriched chondrite-normalized patterns with slightly Eu anomalies. In the primitive mantle-normalized spidergram, both of them are enriched in LIIE including REE, Rb, K and Pb but depleted in HSFE including Nb, Ta, Ti and P. Our research suggests that monzonites have formed the gabbric magma by fractional crystallization. Geochemical data indicate that the parental magma of the Jiasha intrusion have derived from subduction-related metasomatized mantle, and have formed by low-degree partial melting （〈5.0%） of garnet-lherzolite. The primary magmas have undergone extensive crustal contamination and fractional crystallization of olivine and pyroxene during emplacement. Our study suggests that the Jiasha intrusion has an age similar to the magma activities in the nearby Diandongnan-Guixi area, indicating that production of these magmatic rocks are possibly related to extension of lithosphere.
出处
《地球化学》
CAS
CSCD
2013年第6期523-543,共21页
Geochimica
基金
全国危机矿山接替资源找矿项目(2008186)
中国科学院矿床地球化学国家重点实验室"十二五"项目群(SKLODG-ZY125-02)
关键词
辉长岩
二长岩
锆石U-PB定年
地球化学
伸展环境
云南省
gabbros
monzonites
SIMS U-Pb zircon dating
geochemistry
extensional setting
Yunnan Province
