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摘要:
本文报道了聂荣微陆块中新发现的高压麻粒岩锆石U-Pb定年结果及其围岩花岗片麻岩中黑云母Ar-Ar同位素年代学结果。高压麻粒岩中的锆石可分为两类，第一类具有核-边显微结构，核部残留锆石具典型岩浆结晶锆石特征，锆石U-Pb年龄541±8Ma~834±11Ma；第二类锆石具典型的变质锆石成因的结构特征，锆石U-Pb谐和年龄为179.0±1.7Ma。花岗片麻岩中黑云母Ar-Ar坪年龄为166.7±1.1Ma。年代学资料显示麻粒岩与其围岩均具有泛非期的年龄信息，麻粒岩的原岩经历了晚元古代-早古生代造山作用，并于早-中侏罗世发生了峰期高压变质作用改造，该变质事件可能代表着聂荣微陆块与羌南板块的碰撞拼合。伴随着早-中侏罗世的岩浆作用，麻粒岩及其围岩迅速抬升，抬升的时间跨度在13Myr左右，于166.7Ma左右抬升至地壳浅层部位或近地表。
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关键词:
- 高压麻粒岩 /
- 锆石U-Pb定年 /
- 40Ar-39Ar测年 /
- 聂荣微陆块 /
- 青藏高原
Abstract:This paper reports the results of LA-ICP-MS U-Pb dating of the zircon in newly discovered high-pressure granulite, and the Ar-Ar isotopic dating of biotite in granitic gneiss of the surrounding rock of high-pressure granulite on Nyainrong microcontinent. There are two types of zircon in high-pressure granulites, the first type is a core-edge microstructure, the zircon residualed cores with typical features of magmatic zircon, zircon U-Pb age is 541±8Ma~834±11Ma; the second zircon with typical structural characteristics of the causes metamorphic zircon, zircon U-Pb age is 179.0±1.7Ma. In granite gneiss the biotite Ar-Ar plateau age of 166.7±1.1Ma. Age data show both granulite and its surrounding are with the Pan-African age information, granulite protolith experienced a Late Proterozoic-Early Paleozoic orogeny, and in the Early-Middle Jurassic occurred peak high-pressure metamorphic role in transformation, the metamorphic event may be related to a major role in collision which occurred in Bangong Co-Nujiang River suture zone in region it may represent the Nyainrong microcontinent and Qiangnan plate put together. With the Early-Middle Jurassic magmatism, granulite and its surrounding rapidly exhumation, exhumation of the time span is about 13Myr and at about 166.7Ma uplift to shallow parts of the crust or near the surface.
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图 1
藏北安多地区构造简图及聂荣岩群分布图
Figure 1.
Tectonic map of the Amdo area, northern Tibet, showing the distribution of the Nyainrong Group-complex
图 2
安多高压麻粒岩剖面
Figure 2.
Geological cross-section showing high-pressure granulite in the Amdo area
图 3
安多高压麻粒岩野外产状和显微镜照片
Figure 3.
Occurrence and micrographs of high-pressure granulite in the Amdo area, northern Tibet
图 4
安多高压麻粒岩典型锆石CL图像和分析点位
Figure 4.
Representative CL images of the analyzed zircons of high-pressure granulite from Amdo showing the spots
图 5
安多高压麻粒岩锆石U-Pb谐和图
Figure 5.
Zircon U-Pb concordia diagram of high-pressure granulite from Amdo
图 6
锆石稀土元素球粒陨石标准化配分模式(标准化值据Sun and McDonough, 1989)
Figure 6.
Chondrite-normalized REE patterns for the zircons (normalization values after Sun and McDonough, 1989)
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