P-T-t evolution of garnet amphibolites in the Wutai-Hengshan area, North   China Craton: insights from phase equilibria and geochronology

doi:10.1111/jmg.12186

CORC > 北京大学 > 地球与空间科学学院

	P-T-t evolution of garnet amphibolites in the Wutai-Hengshan area, North China Craton: insights from phase equilibria and geochronology
	Qian, J. H. ; Wei, C. J.
刊名	JOURNAL OF METAMORPHIC GEOLOGY
	2016
关键词	garnet amphibolite North China Craton phase equilibria P-T-t evolution zircon dating PARTIAL MELTING EQUILIBRIA EFFECTIVE BULK-COMPOSITION LOWER CRUSTAL SECTION METAMORPHIC EVOLUTION ZIRCON AGES TECTONIC EVOLUTION MINERAL EQUILIBRIA CENTRAL AUSTRALIA HUTUO-GROUP SYSTEM K2O-FEO-MGO-AL2O3-SIO2-H2O-TIO2-FE2O3
DOI	10.1111/jmg.12186
英文摘要	Garnet amphibolites can provide valuable insights into geological processes of orogenic belts, but their metamorphic evolution is still poorly constrained. Garnet amphibolites from the Wutai-Hengshan area of the North China Craton mainly consist of garnet, hornblende, plagioclase, quartz, rutile and ilmenite, with or without titanite and epidote. Four samples selected in a south-north profile were studied by the pseudosection approach in order to elucidate the characteristics of their metamorphic evolution, and to better reveal the northwards prograde change in P-T conditions as established previously. For the sample from the lower Wutai Subgroup, garnet exhibits obvious two-substage growth zoning characteristic of pyrope (X-py) increasing but grossular (X-gr) decreasing outwards in the core, and both X-py and X-gr increasing outwards in the rim. Phase modelling using THERMOCALC suggests that the garnet cores were formed by chlorite breakdown over 7-9 kbar at 530-600 degrees C, and rims grew from hornblende and epidote breakdown over 9.5-11.5 kbar at 600-670 degrees. The isopleths of the minimum An in plagioclase and maximum X-py in garnet were used to constrain the peak P-T conditions of similar to 11.5 kbar/670 degrees. The modelled peak assemblage garnet + hornblende + epidote+ plagioclase + rutile + quartz matches well the observed one. Plagioclase-hornblende coronae around garnet indicate post-peak decompression and fluid ingress. For the samples from the south Hengshan Complex, the garnet zoning weaken gradually, reflecting modifications during decompression of the rocks. Using the same approach, the rocks are inferred to have suprasolidus peak conditions, increasing northwards from 11.5 kbar/745 degrees, 12.5 kbar/780 degrees to 13 kbar/800 degrees. Their modelled peak assemblages involve diopside, garnet, hornblende, plagioclase, rutile and quartz, yet diopside is not observed petrographically. The post-peak decompression is characterized by diopside + garnet + quartz + melt = hornblende + plagioclase, causing the diopside consumption and garnet compositions to be largely modified. Thus, the pesudosection approach is expected to provide better pressure results than conventional thermobarometry, because the later approach cannot be applied with confidence to rocks with multi-generation assemblages. U-Pb dating of zircon in the Wutai sample records a protolith age of c. 2.50 Ga, and a metamorphic age of c. 1.95 Ga, while zircon in the Hengshan samples records metamorphic ages of c. 1.92 Ga. The c. 1.95 Ga is interpreted to represent the prepeak or peak metamorphic stages, and the ages of c. 1.92 Ga are assigned to represent the cooling stages. All rocks in the Wutai-Hengshan area share similar clockwise P-T morphologies. They may represent metamorphic products at different crustal depths in one orogenic event, which included a main thickening stage at c. 1.95 Ga followed by a prolonged uplift and cooling after 1.92 Ga.; National Natural Science Foundation of China [41172055, 41430207]; SCI(E); EI; ARTICLE; jiahui1987@126.com; cjwei@pku.edu.cn; 5; 423-446; 34
语种	英语
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/437189]
专题	地球与空间科学学院
推荐引用方式 GB/T 7714	Qian, J. H.,Wei, C. J.. P-T-t evolution of garnet amphibolites in the Wutai-Hengshan area, North China Craton: insights from phase equilibria and geochronology[J]. JOURNAL OF METAMORPHIC GEOLOGY,2016.
APA	Qian, J. H.,&Wei, C. J..(2016).P-T-t evolution of garnet amphibolites in the Wutai-Hengshan area, North China Craton: insights from phase equilibria and geochronology.JOURNAL OF METAMORPHIC GEOLOGY.
MLA	Qian, J. H.,et al."P-T-t evolution of garnet amphibolites in the Wutai-Hengshan area, North China Craton: insights from phase equilibria and geochronology".JOURNAL OF METAMORPHIC GEOLOGY (2016).