Transition of UHP eclogites to gneissic rocks of low-amphibolite facies during exhumation: evidence from the Dabie terrane, central China

Zhang, Ru Y.; Liou, J. G.; Zheng, Yong Fei; Fu, Bin

doi:10.1016/s0024-4937(03)00102-6

Cited by 92 publications

(59 citation statements)

References 36 publications

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“…We conclude that initial intermineral isotopic equilibrium relationships were either destroyed by fluid-induced recrystallization and isotope transport, or that disequilibria reflect incomplete mixing between rock-derived and isotopically different, fluid-advected Sr. Similar patterns of fluid-induced, arrested retrogression and correlated isotopic disequilibria are well known also from O-H isotope and from combined O isotope/RbSr studies (Zhang et al 2003, Chen et al 2007). It appears that the mobility of trace elements is, as a rule, limited by that of the structure-forming major elements (cf.…”

Section: Temperature Fluids Metamorphic Reactions: What Moves Sr Issupporting

confidence: 68%

Geochronology of fluid-induced eclogite and amphibolite facies metamorphic reactions in a subduction–collision system, Bergen Arcs, Norway

Glodny

Kühn

Austrheim

2007

Contrib Mineral Petrol

119

100

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Rb-Sr multimineral isochron data for metamorphic veins allow to date separate increments of the mineral reaction history of polymetamorphic terranes. Granulite facies rocks of the Lindås nappe, Bergen Arcs, Norway, were subducted and exhumed during the Caledonian orogeny. The rocks show petrographic evidence for two distinct events of local fluid infiltration and vein formation, along fractures and shear zones. The first occurred at eclogite facies (15-21 kbar, 650-750 °C) and a later one at amphibolite facies conditions (8-10 kbar, 600°C). The presence of fluids enabled local metamorphic equilibration only near fluid pathways. In fluid-absent domains, preexisting assemblages were metastably preserved. This resulted in a heterogeneity of metamorphic signatures on m-to µm-scales. Well-preserved granulite facies rocks preserve their Proterozoic Rb-Sr mineral ages, as does the U-Pb system of zircon in most lithologies. Six Rb/Sr multimineral isochron ages for eclogite facies veins and their immediate wallrocks date the fluid-induced eclogitization at 429.9 ± 3.5 Ma (2σ, weighted average, MSWD = 0.39). An eclogite facies vein has yield metamorphic zircon with concordant U-Pb ages of 429 ± 3 Ma, identical to the U-Pb age of 427.4 ± 0.9 Ma for zircon xenocrysts in an amphibolite facies vein. Seven Rb/Sr mineral isochron ages date amphibolite-facies fluid infiltration at 414.2 ± 2.8 Ma (MSWD = 1.5), an age value testifying to residence of the rocks in the deep orogenic crust at temperatures >600°C for nearly 15 Ma. The new data show that Rb-Sr mineral isochron ages effectively date fluid-induced (re)crystallization events rather than stages of cooling. The direct link between isotopic ages and distinct petrographic equilibrium assemblages aids to constrain the evolution of rocks in the P-T-reaction-time space, which is essential for understanding exhumation histories and the internal dynamics of orogens in general.

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Section: Temperature Fluids Metamorphic Reactions: What Moves Sr Issupporting

confidence: 68%

Geochronology of fluid-induced eclogite and amphibolite facies metamorphic reactions in a subduction–collision system, Bergen Arcs, Norway

Glodny

Kühn

Austrheim

2007

Contrib Mineral Petrol

119

100

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“…Completely retrograded eclogites with similar assemblages and textural features from the Dabie UHP terrane have also been reported by R. Y. Zhang et al (2003), and the transformation from quartz eclogite to gneiss was attributed to fluid infiltration and metasomatism along grain boundaries and fractures during the retrograde stage.…”

Section: Completely Retrograded Eclogitesupporting

confidence: 69%

“…The Sulu belt consists of amphibolite-facies granitic orthogneiss, paragneiss, amphibolite, and marble, in which abundant coesite-bearing eclogite, kyanite quartzite, and UHP garnet peridotite/pyroxenite occur as lenses, layers, or blocks (Hirajima et al, 1990;Yang et al, 1993;R. Y. Zhang et al, , 1995R. Y. Zhang et al, , 2003Liou et al, 1995;Cong et al, 1996;Yang and Jahn, 2000).…”

Section: Geological Setting and Ccsd Sample Locationmentioning

confidence: 99%

Assemblages and Textural Evolution of UHP Eclogites from the Chinese Continental Scientific Drilling Main Hole

Tong

Jahn

Iizuka

et al. 2007

International Geology Review

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Coesite-bearing eclogite samples from the Chinese Continental Scientific Drilling main hole (100-2000 m) were examined. Three major evolutionary stages are distinguished from mineral assemblages and textural relations.(1) The pre-peak stage is indicated by inclusion assemblages in rutile eclogite such as amphibole and paragonite, with pre-peak P-T conditions of ~13 kbar and 910ºC. (2) The peak ultrahigh-pressure (UHP) metamorphic stage is characterized by the mineral assemblage garnet-omphacite-phengite-rutile-apatite-coesite/quartz pseudomorph ± kyanite; P-T conditions reached ~910ºC and ~37 kbar for rutile eclogite, and ~850ºC and ~35 kbar for phengite eclogite. (3) The retrograde stage produced decompression textures via back reactions, such as thin coronas of amphibole or zoisite on garnet, fine-grained amphibole-plagioclase symplectites on omphacite and biotite-plagioclase, or K-feldspar-albite on phengite, ilmenite or titanite on rutile, at P-T conditions of 530-560ºC and 7-9 kbar. The presence of K-feldspar-albite symplectite on phengite and minor interstitial K-feldspar implies that post-peak decompressional partial melting occurred locally during rapid exhumation of the subducted UHP slab.Two alternative P-T paths may be constructed: (1) the first possesses a different pre-peak stage but similar peak UHP to post-peak decompression cooling for rutile and phengite eclogite; (2) the second shows a consistent evolution from a pre-peak stage via peak UHP stage to a post-peak stage of near-isothermal decompression, followed by near-isobaric cooling for both rutile and phengite eclogite. We prefer the first P-T path, because the inferred paths show a clear increase in pressure and temperature from near-peak to peak UHP stage, and this may be associated with subductionrelated tectonism as a result of continental collision between the North China and Yangtze blocks. Rapid subduction and fast retrograde exhumation is likely responsible for preservation of some pre-peak inclusion assemblages and prograde mineral growth zoning.

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“…18 O values like associated eclogites (Zheng et al, 1998(Zheng et al, , 2004Fu et al, 1999;Zhang et al, 2003), indicating significant 18 O depletion before plate subduction at Triassic.…”

Section: Geological Backgroundmentioning

confidence: 88%

Protolith age and exhumation history of metagranites from the Dabie UHP metamorphic belt in east-central China: A multi-chronological study

Wang

Fang

et al. 2004

Geochem. J.

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Metagranites (granitic orthogneisses) constitute one of the important lithologic units in the Dabie ultrahigh pressure metamorphic belt. They often display direct contact with paragneisses and eclogites. TIMS zircon U-Pb dating on the metagranites reveal that their protolith was crystallized as granitoids in Neoproterozoic ages of 755 to 611 Ma and thus correspond to rift magmatism associated with breakup of the Rodinia supercontinent in the northern margin of the Yangtze Block. Zircon U-Pb age and Ar-Ar ages of amphibole and biotite indicate that the granitoids experienced eclogite-facies metamorphism in Early Mesozoic with rapid exhumation at cooling rates of 8.7 to 10.2°C/Ma from 225 ± 6 to 181 ± 3 Ma in response to amphibolite-facies retrogression. Fission track ages of sphene, zircon and apatite indicate that the metagranites experienced slow exhumation with cooling rates of 0.88 to 1.25°C/Ma in Late Mesozoic. It is possible that in the first period of exhumation, the metagranites were uplifted from the mantle depth to lower crustal level at ca. 225 Ma, then rapidly reached middle to upper crustal levels between 204 Ma and 180 Ma. After the intensive magmatism in Early Cretaceous, the Dabie terrane was uplifted at the slow rate in response to unroofing. Either the rapid exhumation in the Early Mesozoic or the slow uplift in the Late Mesozoic in the Dabie terrane were contemporaneous with two rapid subsidence and sedimentation of the Hefei Basin in Early Jurassic and Paleogene, respectively. This suggests that the orogeny and basin-forming events were closely related to each other rather than independently separated.Keywords: metagranite, geochronology, cooling history, eclogite-facies, amphibolite-facies to the exact timing of UHP metamorphic event at either Early-middle Triassic or Late Triassic.In the Dabie UHP metamorphic belt, granitic orthogneisses are widespread Cong, 1996), which is termed as metagranites in this paper following the nomenclature of Xu et al. (1998). It was suggested that these metagranites did not experience the UHP metamorphism because no UHP index mineral was found until 2001. However, this suggestion was questioned by Carswell et al. (2000), who deduced from mineralogy and mineral chemistry that the metagranites were metamorphosed at P-T conditions of 36 to 18 kbar and 750 to 690°C. Furthermore, coesite inclusions were observed in zircons by Liu, F-L. et al. (2001) and Liu, J-B. et al. (2001), demonstrating that the metagranites did experience the UHP metamorphism.With respect to ages of metagranite protolith and UHP event in the Dabie terrane, a number of zircon U-Pb dating was carried out by the TIMS technique. The results show discordia upper and lower intercept ages of 800 to

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Transition of UHP eclogites to gneissic rocks of low-amphibolite facies during exhumation: evidence from the Dabie terrane, central China

Cited by 92 publications

References 36 publications

Geochronology of fluid-induced eclogite and amphibolite facies metamorphic reactions in a subduction–collision system, Bergen Arcs, Norway

Geochronology of fluid-induced eclogite and amphibolite facies metamorphic reactions in a subduction–collision system, Bergen Arcs, Norway

Assemblages and Textural Evolution of UHP Eclogites from the Chinese Continental Scientific Drilling Main Hole

Protolith age and exhumation history of metagranites from the Dabie UHP metamorphic belt in east-central China: A multi-chronological study

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