Discovery of coesite in the North Qaidam Early Palaeozoic ultrahigh pressure (UHP) metamorphic belt, NW China

Yang, Jingsui; Xu, Zhiqin; Song, Shuguang; Zhang, Jianxin; Wu, Cailai; Shi, Rui; Li, Haibing; Brunel, Maurice

doi:10.1016/s1251-8050(01)01718-9

Cited by 61 publications

(79 citation statements)

References 8 publications

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“…These K -Ar ages pertain to the later stage of metamorphism, i.e., after the UHPM. These ages of ~ 500 Ma are comparable with the UHPM ages of the Kokchetav and of the North Qaidam (Katayama et al, 2001;Yang et al, 2001;Rumble et al, 2005).…”

Section: Occurrence Of Coesite and Coesite-pseudomorph And K-ar Agesupporting

confidence: 73%

Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

Tagiri

Takiguchi²,

Ishida

et al. 2010

Journal of Mineralogical and Petrological Sciences

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Coesite occurs in garnets from quartz schists and pelitic schists in the Makbal Complex of Kyrgyzian TienShan. The thick quartz schists interbedded with pelitic schists are the transitional facies after coesite schists. Quartz -pseudomorph after coesite also appears widely in pelitic schists and quartz schists, but is rare in eclogitic rocks. The growth zoning of garnets and Na -Ca amphiboles in eclogites and the garnet -omphacite geothermometry indicate that the metamorphic P -T paths of eclogites are different from each. Ultra -high (UHP) pressure metamorphic rocks of the Makbal Complex are mainly composed of pelitic and quartz schists. All eclogite lenses are included in the host UHPM rocks, although most of them do not contain UHP metamorphic (UHPM) evidences. The K -Ar ages of phengite in a host pelitic schist and of paragonite in an eclogite are approximately 500 Ma, while those of biotite and phengite in a biotite -bearing mica schist and of winchite in a winchite schist are approximately 769 -717 Ma and 881 Ma, respectively. The evidence indicates that this complex is a tectonic mélange. These geological relationships suggest that the ascending substances must be pelitic and quartz schists. The UHPM rocks in the ascending material capture many exotic blocks as xenoliths during intrusion into the upper crust.

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Section: Occurrence Of Coesite and Coesite-pseudomorph And K-ar Agesupporting

confidence: 73%

Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

Tagiri

Takiguchi²,

Ishida

et al. 2010

Journal of Mineralogical and Petrological Sciences

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“…The existence of UHP paragneisses [6,7,27,28] indicates that continent deep subduction occurred along the present north Qinling-north Qaidam-Altun HP/UHP metamorphic belt, and that the north Qinling (Qinling Group), Qaidam and some other micro-continents had been collided and assembled at ~500 Ma.…”

Section: Implication and Discussionmentioning

confidence: 99%

Electron microprobe chemical ages of monazite from Qinling Group in the Qinling Orogen: Evidence for Late Pan-African metamorphism?

Chen

Wang

et al. 2006

CHINESE SCI BULL

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Electron microprobe chemical dating was carried out on monazites enclosed in two generations of mineral paragenesis of St + Ky + Grt and Sil + And + Grt + St, respectively, from the Qinling Group. Two different ages, 520±23 Ma and 435±9 Ma, were obtained from these monazites. This indicates that the Qinling Group experienced a metamorphism during the Early Cambrian, which is probably in response to the Late Pan-African subduction-accretion tectonothermal event.

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“…Over the past ten years, a new HP/UHP metamorphic terrane has been confirmed along the north Qaidam Mountains in western China [1][2][3][4][5][6][7][8][9][10][11][12][13] . It has been correlated to the south Altyn Tagh HP/UHP metamorphic terrane, and constrains a 400 km offset for the Altyn Tagh fault.…”

Section: Coesite and Its Pseudomorphs Have Not Been Found In Eclogitementioning

confidence: 99%

“…On the basis of spatial relations, rock associations and metamorphic evolution of eclogites and associated rocks, two subbelts, namely, the South Dulan Belt (SDB) and the North Dulan Belt (NDB), are recognized [3,11] . These two sub-belts are separated by the Yematan granitic pluton.…”

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confidence: 99%

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Coesite in eclogite from the North Qaidam Mountains and its implications

Zhang

Meng

et al. 2009

Sci. Bull.

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Coesite provides direct evidence for ultrahigh pressure metamorphism. Although coesite has been found as inclusions in zircon in paragneiss of the north Qaidam Mountains, it has never been identified in eclogite. In this contribution, based on petrographic observations and in situ Raman microprobe spectroscopy, coesite was identified as inclusions in garnet of eclogite from the Aercituoshan, Dulan UHP metamorphic unit, north Qaidam Mountains. Coesite is partly replaced by quartz, showing a palisade texture. This is the first report on coesite in eclogite from the north Qaidam Mountains, and is also supported by garnet-omphacite-phengite geothermobarometry (2.7-3.25 GPa, 670-730℃). Coesite and its pseudomorphs have not been found in eclogites and associated rocks of other units of the north Qaidam Mountains. Further studies are required to confirm if all metamorphic units in the north Qaidam Mountains underwent the ultrahigh-pressure metamorphism.North Qaidam Mountains, Dulan, eclogite, coesite, Ultrahigh pressure metamorphismThe ultrahigh-pressure (UHP) metamorphism refers to the metamorphism above the coesite-quartz transition. Therefore, although a number of mineralogical indicators have been considered as evidence for UHP metamorphism, coesite is still one of the most direct indicators for UHP metamorphism.Over the past ten years, a new HP/UHP metamorphic terrane has been confirmed along the north Qaidam Mountains in western China [1][2][3][4][5][6][7][8][9][10][11][12][13] . It has been correlated to the south Altyn Tagh HP/UHP metamorphic terrane, and constrains a 400 km offset for the Altyn Tagh fault. Therefore, South Altyn-North Qaidam was considered as a single HP-UHP metamorphic belt truncated by a large strike-slip fault, similar to the case of the Dabie-Sulu HP-UHP metamorphic zone which was truncated by the sinistral Tanlu strike-slip fault in eastern China, and split into the Dabie and Sulu regions [14][15][16][17][18][19][20][21] . However, in contrast to Dabie-Sulu in eastern China, where UHP metamorphic evidence has been commonly recognized in different rock types, evidence of UHP metamorphism is relatively rare in the north Qaidam (NQD) and south Altyn Tagh (SAT) [11,22,23] . Up to now, coesite was only reported as inclusions in zircons of amphibolite-facies paragneiss in the Dulan area, eastern NQD. This high-pressure silica polymorph has never been positively identified in eclogite from the NQD and SAT. Although polycrystalline quartz inclusions in garnet and omphacite in the Jianggelesayi eclogite of SAT and Dulan eclogite of NQD were interpreted as pseudomorphs after coesite, the polycrystalline aggregates cannot be simply the result of a transformation from coesite because they contain small amounts of K-feldspar [24,25] .Recently, detailed field work and petrographic observations have led to the first discovery of coesite inclusions in garnet of eclogite in the northern slope of Aercituoshan, southern Dulan HP/UHP metamorphic unit, north Qaidam Mountains.

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Discovery of coesite in the North Qaidam Early Palaeozoic ultrahigh pressure (UHP) metamorphic belt, NW China

Cited by 61 publications

References 8 publications

Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

Electron microprobe chemical ages of monazite from Qinling Group in the Qinling Orogen: Evidence for Late Pan-African metamorphism?

Coesite in eclogite from the North Qaidam Mountains and its implications

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