ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00164.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTen metamorphic domains can be distinguished in China, comprising four cratonic, three intracratonic and three intercratonic domains. Each domain contains one or more metamorphic belts, each of which, in turn, contains a characteristic metamorphic facies or facies series that was formed during a distinct metamorphic epoch.The metamorphic domains reflect the tectonic domains and tectonic evolution of China. Ancient continental nucleii in the North China and Tarim–Alxa cratons were probably unified with the Yangtze craton during the Early Proterozoic to form the China Platform. Widespread greenschist facies metamorphism, during the Middle and Late Proterozoic, accompanied by glaucophane–greenschist facies metamorphism, represents a rifting and closure event in the China Platform; a second rifting and closure event in the China Platform occurred during the Caledonian. The China and Siberian platforms were closed during the Hercynian to form the Eurasian Continent. Closure of the ancient Tethys Ocean occurred in the Indosinian epoch, and subduction and collision within Xizang (Tibet) and Taiwan occurred during Mesozoic–Cenozoic time.The distribution in time of types of metamorphism in China suggests cyclical changes of metamorphism known as the Archaean, Proterozoic and Phanerozoic megacycles. Each megacycle since the Archaean consists of a change from progressive, low‐ to intermediate‐grade metamorphism to lower grade, greenschist metamorphism that was superimposed on a general trend in which high‐grade metamorphism became progressively less important with time. The change in metamorphic megacycles shows a general secular decrease in regional heat supply during metamorphism punctuated by episodic high‐grade, progressive metamorphism within o

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00165.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe widespread khondalite series of south‐east Inner Mongolia consists largely of biotite–sillimanite–garnet gneiss and quartzo‐feldspathic gneiss with some marble and mafic granulite layers. It has experienced two metamorphic events atc.2500 and 1900–2000 Ma.A pre‐peak stage of the first metamorphism atT= 600–700°C andP>6–7 kbar is recognized by the relict amphibolite facies assemblage Ky–Grt–Bt–Pl–Qtz and ‘protected’inclusions of biotite, hornblende, sodic plagioclase and quartz in garnet or orthopyroxene. The peak stage, withT=c.800 ± 50°C andP8–10 kbar, is characterized by the widespread granulite facies assemblages Sil–Grt–Bt–Kfs–Pl–Qtz in gneiss and Opx–Cpx–Pl ± Hbl ± Grt in granulite. TheP–T–tpath suggests that the supracrustal sequence was buried in the lower crust by tectonic thickening during D1–D2.The beginning of the second metamorphism is characterized by further temperature rise to 700°C or more at lower pressure. This stage is manifested by the appearance of cordierite after garnet, fibrolite (Sil2) after biotite in gneiss and transformation of Hbl1 into Opx2 and Cpx2 in granulite. Coronas of symplectitic Opx2 + Pl2 surrounding Grt1 and Cpx1 in mafic granulite are interpreted as products of near‐isothermal decompression. TheP–T–tpath may be related tectonically to wani

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00166.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractArchaean and Proterozoic granulite facies complexes of Inner Mongolia differ in lithological association, tectonic style, mineral assemblage and metamorphicP–Tpath. A nearly isobaric cooling path for Archaean high‐grade metamorphic rocks is suggested by reaction textures and geothermobarometry. Early Proterozoic metamorphic rocks show nearly isothermal decompression. Archaean metamorphism may have been caused by magmatic accretion, whereas early Proterozoic metamorphism suggests a major continental thickening event followed by exhumat

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00167.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractRegional metamorphism in central Inner Mongolia has occurred during four different periods: the middle Proterozoic, the early Palaeozoic, the middle Palaeozoic and the late Palaeozoic tectonic cycles. The middle Proterozoic and late Palaeozoic metamorphic events are associated with rifting and are characterized by low‐pressure facies series. The early Palaeozoic metamorphism occurred in two stages: (1) subduction zone metamorphism resulted in paired metamorphic belts in the Ondor Sum ophiolite and Bainaimiao island arc complex; and (2) orogenic metamorphism occurred during the collision of an island arc with the continent. Two types of middle Palaeozoic metamorphism are represented: (1) subduction zone metamorphism, which affected the melange; and (2) orogenic metamorphism that resulted from continent–continent collis

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00168.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo blueschist belts in the North Qilian Mountains occur in Middle Cambrian and Lower Ordovician strata and strike N30–35°W for about 500 km along the Caledonian fold belt on the south‐west margin of the Sino‐Korean plate. The styles of metamorphism and deformation are quite different in the two belts. The Middle Cambrian to Ordovician rocks in the high‐grade belt are mainly blueschists and C‐type eclogites in which six phases of lower and upper crustal deformation have been recognized. The rocks contain glaucophane, phengite, epidote, clinozoisite, chlorite, garnet, stilpnomelane, piedmontite, albite, titanite and quartz. The estimatedP–Tconditions of eclogites are 340 ± 10°C, 8 ± 1 kbar and, of blueschist,>380°C, 6–7 kbar. The Ordovician rocks in the low‐grade belt are characterized by ductile to brittle deformation in the middle to upper crust. The low‐grade blueschists contain glaucophane, lawsonite, pumpellyite, aragonite, albite and chlorite. The estimatedP–Tconditions are 150–250°C and 4–7 kbar.K–Ar and39Ar/40Ar geochronology on glaucophane and phengite from the high‐grade blueschist belt suggest two stages of metamorphism at 460–440 and 400–380 Ma, which may represent the times of subduction and orogeny. The subduction metamorphism of the northern low‐grade blueschist belt took place app

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00169.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Shangdan fault in the Qinling Orogenic Belt of China is an important boundary between the Caledonian North Qinling Fold Belt and the Hercynian South Qinling Fold Belt. In the Danfeng area, the fault zone strikes WNW–ESE and comprises four strongly deformed zones and three weakly deformed domains parallel to each other. The fault zone has a complex history of multiple deformation and each domain has a different tectonic style that was formed at different stages of the deformation.The rocks exposed in the weakly deformed domains belong to the Qinling, Danfeng and Liuling Groups. In this paper, the mineral chemistry and mineral assemblages are used to infer the metamorphic conditions and theP–Tpaths of these units. The metamorphic units in and near the fault zone have different metamorphic conditions and histories that are correlated with the tectonic evolution of the fault zone. Caledonian–Hercynian uplift and southward thrusting of the Proterozoic Qinling Group, over the Danfeng and the Liuling Groups, produced the main metamorphic and tectonic features of the fault zone. Folding of both the Liuling Group and the thrust faults during the Hercynian–Indosinian was accompanied by northward th

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00170.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe metamorphic history and tectonic evolution of the Qinling Complex is divided into formation and modification stages. During the Proterozoic formation stage, three deformational sequences are recognized. Andalusite–muscovite, sillimanite–muscovite and sillimanite–K‐feldspar zones of amphibolite facies regional metamorphism are earlier than, or synchronous with the first or second phase of folding. Ductile shear zones were formed and Caledonian granites were emplaced during the modification stage. The granites superimposed contact aureoles (garnet–K‐feldspar zone) on the regional metamorphic fabric.Metamorphic reactions,P–Tconditions of metamorphism andP–T–tpaths were estimated by analysis of mineral textures and standard thermobarometric techniques. TheP–T–tpath of the Proterozoic tectonometamorphic cycle shows prominent clockwise decompression. TheP–T–tpath of the Caledonian tectonometamorphic cycle is characterized by an early rise of pressure and temperature, followed by isothermal decompression (rapid uplift) and finally with isobaric cooling.TheP–T–tpaths of the two tectonometamorphic cycles reflect two major stages of collision and uplift in the evolution of the Qinling orogenic belt during the Proterozoic and Caledonian–

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00171.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Qinling–Dabie accretionary fold belt in east‐central China represents the E–W trending suture zone between the Sino‐Korean and Yangtze cratons. A portion of the accretionary complex exposed in northern Hubei Province contains a high‐pressure/low‐temperature metamorphic sequence progressively metamorphosed from the blueschist through greenschist to epidote–amphibolite/eclogite facies. The ‘Hongan metamorphic belt’can be divided into three metamorphic zones, based on progressive changes in mineral assemblages: Zone I, in the south, is characterized by transitional blueschist–greenschist facies; Zone II is characterized by greenschist facies; Zone III, in the northernmost portion of the belt, is characterized by eclogite and epidote–amphibolite facies sequences. Changes in amphibole compositions from south to north as well as the appearance of increasingly higher pressure mineral assemblages toward the north document differences in metamorphicP–Tconditions during formation of this belt. PreliminaryP–Testimates for Zone I metamorphism are 5–7 kbar, 350–450°C; estimates for Zone III eclogites are 10–22 kbar, 500 ± 50°C.The petrographic, chemical and structural characteristics of this metamorphic belt indicate its evolution in a northward‐dipping subduction zone and subsequent uplift prior to and during the final collision between

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00172.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractWidespread ultra‐high‐Passemblages including coesite, quartz pseudomorphs after coesite, aragonite, and calcite pseudomorphs after aragonite in marble, gneiss and phengite schist are present in the Dabie Mountains eclogite terrane. These assemblages indicate that the ultra‐high‐Pmetamorphic event occurred on a regional scale during Triassic collision between the Sino‐Korean and Yangtze cratons. Marble in the Dabie Mountains is interlayered with coesite‐bearing eclogite and gneiss and as blocks of various size within gneiss. Discontinuous boudins of eclogite occur within marble layers. Marble contains an ultra‐high‐Passemblage of calcite/aragonite, dolomite, clinopyroxene, garnet, phengite, epidote, rutile and quartz/coesite. Coesite, quartz pseudomorphs after coesite, aragonite and calcite pseudomorphs after aragonite occur as fine‐grained inclusions in garnet and omphacite. Phengites contain about 3.6 Si atoms per formula unit (based on 11 oxygens). Similar to the coesite‐bearing eclogite, marble exhibits retrograde recrystallization under amphibolite–greenschist facies conditions generated during uplift of the ultra‐high‐Pmetamorphic terrane. Retrograde minerals are fine grained and replace coarse‐grained peak metamorphic phases. The most typical replacements are: symplectic pargasitic hornblende + epidote after garnet, diopside + plagioclase (An18) after omphacite, and fibrous phlogopite after phengite. Ferroan pargasite + plagioclase, and actinolite formed along grain boundaries between garnet and calcite, and calcite and quartz, respectively.The estimated peakP–Tconditions for marble are comparable to those for eclogite: garnet–clinopyroxene geothermometry yields temperatures of 630–760°C; the garnet–phengite thermometer gives somewhat lower temperatures. The minimum pressure of peak metamorphism is 27 kbar based on the occurrence of coesite. Such estimates of ultra‐high‐Pconditions are consistent with the coexistence of grossular‐rich garnet + rutile, and the high jadeite content of omphacite in marble. The fluid for the peak metamorphism was calculated to have a very lowXCO2(<0.03). TheP–Tconditions for retrograde metamorph

ISSN:0263-4929    

DOI:10.1111/j.1525-1314.1993.tb00173.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY