Combined rutile-zircon thermometry and U-Pb geochronology: New constraints on Early Paleozoic HP/UHT granulite in the south Altyn Tagh, north Tibet, China

doi:10.1016/j.lithos.2014.05.006

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	Combined rutile-zircon thermometry and U-Pb geochronology: New constraints on Early Paleozoic HP/UHT granulite in the south Altyn Tagh, north Tibet, China
	Zhang, J. X.5; Mattillson, C. G.; Yu, S. Y.; Li, Y. S.
刊名	LITHOS
	2014
卷号	200 页码:241-257
关键词	HP/UHT granulite South Altyn Tagh Rutile-zircon thermometry U-Pb geochronology
ISSN号	0024-4937
DOI	10.1016/j.lithos.2014.05.006
英文摘要	HP granulite and garnet peridotite constitute a HP metamorphic unit in the south Altyn Tagh, northern Tibet. Previous data suggest that HP granulites experienced high pressure, ultrahigh-temperature metamorphism (870-1050 degrees C, 19-25 kbar), followed by a medium pressure granulite facies overprint (780-820 degrees C, 9.5-12 kbar). Previous zircon U-Pb geochronology of HP granulites gave an age of ca. 500 Ma, but it is unclear if this age reflects the metamorphic peak, or the post-peak overprint. In this contribution, new SHRIMP analyses indicate that the zircons associated with the peak metamorphic assemblage in HP felsic granulite are characterized by flat heavy REE patterns and 30-62 ppm Ti, yielding a temperature of 892-1002 degrees C by Ti-in-zircon thermometry, suggesting that the growth of the zircons occurred under or close to peak ultrahigh-temperature conditions rather than under post-peak conditions. These zircons gave a SHRIMP U-Pb age of 495 +/- 4 Ma, representing the age of peak metamorphism. In contrast, oscillatory zoned zircon cores yield magmatic REE patterns, Ti-in-zircon temperatures of 720-820 degrees C, and Neoproterozoic U-Pb ages (936 +/- 22 Ma). This indicates that the protoliths of the felsic granulites were formed in the early Neoproterozoic and were taken to extreme temperatures and pressures during the early Paleozoic orogenic event. In situ LA-ICPMS and EMP analyses indicate that rutiles are characterized by broad scatter and bimodal distribution in both Zr concentration and U-Pb age, which are interpreted as a result of recrystallization or growth rather than volume diffusion. The first rutile U-Pb age cluster is at ca. 485 Ma with a Zr concentration of ca. 3000 ppm, yielding ca. 950 degrees C at 20 kbar, implying that they grew at or near the peak metamorphic conditions. The second rutile U-Pb age cluster is at ca. 450 Ma with a Zr concentration of ca. 1000 ppm, corresponding to a temperature around 780 degrees C at 10 kbar, which is related to post-peak reheating under medium pressure/medium temperature granulite facies conditions. These results demonstrate that HP granulites in the south Altyn Tagh experienced a peak ultrahigh temperature and high pressure metamorphism at ca. 495 Ma, followed by medium pressure/medium temperature granulite facies overprint before ca. 450 Ma. (C) 2014 Elsevier B.V. All rights reserved.
学科主题	变质岩岩石学
WOS关键词	HIGH-PRESSURE GRANULITES ; BOHEMIAN MASSIF ; NW CHINA ; GEOLOGICAL SIGNIFICANCE ; NORTHWESTERN CHINA ; WESTERN SEGMENT ; CRUSTAL ROCKS ; GREENLAND CALEDONIDES ; METAMORPHIC TERRANE ; MOLDANUBIAN ZONE
WOS研究方向	Geochemistry & Geophysics ; Mineralogy
语种	英语
出版者	ELSEVIER SCIENCE BV
WOS记录号	WOS:000338810700017
内容类型	期刊论文
源URL	[http://119.78.100.197/handle/2HKVOGP0/40475]
专题	中国地质调查局
作者单位	1.[Zhang, J. X. 2.Yu, S. Y. 3.Li, Y. S.] CAGS, Inst Geol, Beijing 100037, Peoples R China 4.[Mattillson, C. G.] Cent Washington Univ, Dept Geol Sci, Ellensburg, WA 98926 USA 5.中国地质科学院地质研究所
推荐引用方式 GB/T 7714	Zhang, J. X.,Mattillson, C. G.,Yu, S. Y.,et al. Combined rutile-zircon thermometry and U-Pb geochronology: New constraints on Early Paleozoic HP/UHT granulite in the south Altyn Tagh, north Tibet, China[J]. LITHOS,2014,200:241-257.
APA	Zhang, J. X.,Mattillson, C. G.,Yu, S. Y.,&Li, Y. S..(2014).Combined rutile-zircon thermometry and U-Pb geochronology: New constraints on Early Paleozoic HP/UHT granulite in the south Altyn Tagh, north Tibet, China.LITHOS,200,241-257.
MLA	Zhang, J. X.,et al."Combined rutile-zircon thermometry and U-Pb geochronology: New constraints on Early Paleozoic HP/UHT granulite in the south Altyn Tagh, north Tibet, China".LITHOS 200(2014):241-257.