摘要
利用LA-ICPMS对采集自汉诺坝大麻坪玄武岩中的两个143Nd/144Nd比值最低[εNd(0)=-26.8～-29.5]的中性麻粒岩包体的单颗粒锆石U-Pb年代学进行了研究,获得了2444Ma和2494Ma的上交点年龄和88Ma的下交点年龄,反映它们是新太古代形成的受到中生代岩浆底侵-热变质作用影响的下地壳麻粒岩。这些包体与周坝玄武岩中～1.9Ga的长英质麻粒岩包体共同确证了华北克拉通北缘目前的下地壳中仍然残留有前寒武纪下地壳岩石。结合区域构造演化历史和DMP-70的层状堆晶特征,推断其原岩形成于～2.5Ga岩浆底侵事件。
Zircons recovered from two intermediate granulite xenoliths are highly discordant with upper intercepts of 2.4～2.5 Ga and lower intercepts of 88 Ma, thus showing evidence for an Archean protolith that was severely overprintedby the Mesozoic magmatic underplating and metamorphism. These two xenoliths have very low unradiogenic Nd isotopic compositions with εNd(0)=-26.8～-29.5. The 2.4～2.5 Ga intermediate granulites from Damaping together with the ～1.9 Ga felsic granulite xenoliths from Zhouba confirm that there are still Precambrian lower crustal rocks in the present day lower crust of the North China craton. Combined with the geologic setting, the layered cumulating structure of DMP 70 suggests that they could be formed by the 2.4～2.5 Ga magmatic underplating. Their geochemical compositions indicate that the magma could be derived frompartial melting of a mantle metasomatized by slab melt.
出处
《地球化学》
CAS
CSCD
北大核心
2004年第3期261-268,共8页
Geochimica
基金
国家自然科学基金(40133020
40003004)
国家"973"项目(2003CB716501)
西北大学地质系大陆动力学教育部重点开放实验室基金
