Fluids in Granulite Facies Metamorphism: A Comparative Oxygen Isotope Study on the South India and Adirondack High-Grade Terrains

1988 ◽  
Vol 96 (5) ◽  
pp. 517-533 ◽  
Author(s):  
Jianxin Jiang ◽  
Robert N. Clayton ◽  
Robert C. Newton
Keyword(s):  
Oxygen Isotope ◽  
South India ◽  
Granulite Facies ◽  
High Grade ◽  
The South ◽  
Granulite Facies Metamorphism ◽  
Facies Metamorphism ◽  
Isotope Study

Silicate, Oxide and Sulphide Trends in Neo-Archean Rocks from the Nilgiri Block, Southern India: the Role of Fluids During High-grade Metamorphism

2019 ◽  
Vol 60 (5) ◽  
pp. 1027-1062 ◽  
Author(s):  
Vinod O Samuel ◽  
Daniel E Harlov ◽  
Sanghoon Kwon ◽  
K Sajeev
Keyword(s):  
Granulite Facies ◽  
Southern India ◽  
Sulphide Mineral ◽  
High Grade ◽  
Regional Trend ◽  
Granulite Facies Metamorphism ◽  
Facies Metamorphism ◽  
High Grade Metamorphism ◽  
Specific Oxidation

Abstract The Nilgiri Block, southern India represents an exhumed section of lower, late Archean (2500 Ma) crust. The northern highlands of the Nilgiri Block are characterized by metagabbros with pyroxenite inlayers. A two-pyroxene granulite zone acts as a transition between the metagabbros and charnockites, which are exposed in the central and southern part of the Nilgiri highlands. Thermobarometry results indicate a SW–NE regional trend both in temperature (∼650–800°C) and in pressure (700–1100 MPa) over the Nilgiri highlands. In the charnockites, composite rutile–ilmenite grains are the dominant oxide assemblage. In the two-pyroxene granulites, hemo-ilmenite–magnetite is dominant with coexisting rutile–ilmenite composite grains in a few samples in the vicinity of the boundary with the charnockites. In the metagabbros, hemo-ilmenite–magnetite is the dominant oxide assemblage. The principal sulphide mineral in the charnockite is pyrrhotite with minor pyrite–chalcopyrite exsolution lamellae or blebs. In the two-pyroxene granulites and the metagabbros, the principal sulphide assemblage consists of discrete pyrite grains with magnetite rims and pyrite–pyrrhotite–chalcocopyrite associations. From these observations, a specific oxidation trend is seen. The northern granulite-facies metagabbros and two-pyroxene granulites of the Nilgiri highlands are highly oxidized compared with the charnockites from the central and southern regions. This higher oxidation state is proposed to be the result of highly oxidizing agents (probably as SO3) in low H2O activity grain boundary NaCl saline fluids with a dissolved CaSO4 component present during granulite-facies metamorphism of the metagabbros and two-pyroxene granulites. Eventually these agents became more reducing, owing to the inherent buffering of the original tonalite–granodiorite granitoids at the graphite–CO2 buffer, such that S took the form of H2S during the granulite-facies metamorphism of the charnockites. At the same time, these saline fluids were also responsible the solid-state conversion of biotite and amphibole to orthopyroxene and clinopyroxene in the metagabbro, two-pyroxene granulite, and charnockite.

SHRIMP U–Pb zircon geochronology of gneisses from the Gweta borehole, northeast Botswana: implications for the Palaeoproterozoic Magondi Belt in southern Africa

2001 ◽  
Vol 138 (3) ◽  
pp. 299-308 ◽  
Author(s):  
R. B. M. MAPEO ◽  
R. A. ARMSTRONG ◽  
A. B. KAMPUNZU
Keyword(s):  
Central Zone ◽  
Granulite Facies ◽  
Eastern Africa ◽  
High Grade ◽  
Zircon Geochronology ◽  
Granulite Facies Metamorphism ◽  
Grade Metamorphism ◽  
Facies Metamorphism ◽  
High Grade Metamorphism ◽  
Limpopo Belt

This paper presents new U–Pb zircon analyses from garnet–sillimanite paragneisses from the Gweta borehole in northeast Botswana. Concordant to near-concordant analyses of zircon from these rocks reveal a billion year history from 3015 ± 21 Ma for the oldest detrital grain measured, to the age of high-grade metamorphism, 2027 ± 8 Ma. The maximum age of sedimentation in the Magondi belt is constrained by the age of the youngest concordant detrital zircon at 2125 ± 6 Ma. This contrasts with the age of sedimentation in the Central Zone of the Limpopo belt which is Archaean. The comparison of our results with U–Pb zircon data from the Magondi belt in Zimbabwe suggests that the granulite-facies metamorphism in this belt extended between c. 2027–1960 Ma. Granulite-facies rocks with U–Pb zircon ages in this interval are also known in the Ubendian belt and lend support to the correlation of these two segments of Palaeoproterozoic belts in southern and central–eastern Africa. The granulite facies metamorphism in the Magondi belt is coeval with the high-grade metamorphism and granitoids documented further south in the Central Zone of the Limpopo Belt.

Accretion and evolution of an Archaean high-grade grey gneiss – amphibolite complex: the Fiskefjord area, southern West Greenland

1997 ◽  
pp. 1-115 ◽  
Author(s):  
Adam A. Garde
Keyword(s):  
Continental Crust ◽  
Granulite Facies ◽  
Ductile Deformation ◽  
Repeated Injection ◽  
High Grade ◽  
Volcanic Origin ◽  
Granulite Facies Metamorphism ◽  
West Greenland ◽  
Facies Metamorphism ◽  
Grey Gneiss

NOTE: This monograph was published in a former series of GEUS Bulletin. Please use the original series name when citing this series, for example: Garde, A. A. 1997: Accretion and evolution of an Archaean high-grade grey gneiss – amphibolite complex: the Fiskefjord area, southern West Greenland. Geology of Greenland Survey Bulletin 177, 115 pp. _______________ The Fiskefjord area in southern West Greenland, part of the Akia tectono-stratigraphic terrane, comprises a supracrustal association and two groups of grey quartzo-feldspathic orthogneises c. 3200 and 3000 Ma old. The supracrustal association forms layers and enclaves in grey gneiss and may comprise two or more age groups. Homogeneous amphibolite with MORB-like but LIL element enriched tholeiitic composition predominates; part, associated with cumulate noritic and dunitic rocks, represents fragments of layered complexes. Heterogeneous amphibolite of likely submarine volcanic origin, (basaltic) andesitic amphibolite, leucogabbro-anorthosite, and minor pelitic metasediment occur. Disruption by magmatic and tectonic events and geochemical alteration have obscured primary origin: the supracrustal association may represent oceanic crust. Grey orthogneiss of the tonalite-trondhjemite-granodiorite (TTG) association was generated during continental accretion at c. 3000 Ma, most likely by partial melting of wet and hot tholeiitic basaltic rocks subducted in a convergent plate setting. Most dioritic gneiss is c. 220 Ma older. A 3040 Ma dioritic to tonalitic phase, enriched in P2O5 , Ba, Sr, K, Pb, Rb and LREE, probably was derived from metasomatised mantle. Intense deformation and metamorphism accompanied the 3000 Ma magmatic accretion.Thrusts along amphibolite-orthogneiss contacts were succeeded by large recumbent isoclines, upright to overturned folds, and local domes with granitic cores. Syntectonic granulite facies metamorphism is thought to be due to heat accumulation by repeated injection of tonalitic magma. Strong ductile deformation produced steep linear belts before the thermal maximum ceased, whereby folds were reorientated into upright south-plunging isoclines. Two large TTG complexes were then emplaced, followed by granodiorite and granite. Post-kinematic diorite plugs with unusually high MgO, Cr and Ni, and low LIL and immobile incompatible element contents, terminated the 3000 Ma accretion. Hybrid border zones and orbicular textures suggest rapid crystallisation from superheated magma. The diorites most likely formed from ultramafic magma contaminated with continental crust. Widespread high-grade retrogression preserved a granulite facies core in the south-west; to the east the retrogressed gneiss grades into amphibolite facies gneiss not affected by granulite facies metamorphism and retrogression. LIL elements were depleted during granulite facies metamorphism and reintroduced during retrogression, probably transported in anatectic silicate melts and in fluids. Rb-Sr isotope data, and relationships between retrogression, high-strain zones and granite emplacement, show that retrogression took place shortly after the granulite facies metamorphism, before terrane assembly at c. 2720 Ma, probably by movement of melts and fluids into the upper, marginal zone of granulite facies rocks from deeper crust still being dehydrated. Retrogression during Late Archaean terrane assembly was in narrow reactivated zones of ductile deformation; in the Proterozoic it occurred with faulting and dyke emplacement.Geochemical data are presented for Early Proterozoic high-Mg and mafic dykes. A rare 2085 Ma microgranite dyke strongly enriched in incompatible trace elements was formed by partial anatexis of Archaean continental crust.  

Regional geothermobarometry in the granulite facies terrane of South India

1983 ◽  
Vol 73 (4) ◽  
pp. 221-244 ◽  
Author(s):  
M. Raith ◽  
P. Raase ◽  
D. Ackermand ◽  
R. K. Lal
Keyword(s):  
South India ◽  
Analytical Data ◽  
Granulite Facies ◽  
Critical Discussion ◽  
Granulite Facies Metamorphism ◽  
Northern Margin ◽  
Mineral Equilibria ◽  
Metamorphic History ◽  
Facies Metamorphism ◽  
History Of

ABSTRACTIn the southern part of the Archaean craton of South India, an approximately 3.4–2.9 b.y. old migmatite–gneiss terrane (Peninsular gneiss complex) has been subjected to granulite facies metamorphism about 2.6 b.y. ago. During this event, the extensive charnockite-khondalite zone of southern India developed. A younger metamorphism (Proterozoic?) led to retrogression of the charnockites and khondalites, mainly under the conditions of the amphibolite facies.The physical conditions of metamorphism have been evaluated by applying methods of geothermobarometry to the widespread charnockitic assemblages with garnet, orthopyroxene, clinopyroxene, plagioclase, and quartz. The interpretation of the P–T estimates includes a critical discussion of potential error sources, e.g. errors of the analytical data and the calibrations of the models, and takes into account the complex metamorphic history of the rocks and the kinetics of the mineral equilibria.P-T estimates were obtained for seven subareas from the rim compositions of the coexisting minerals: Shevaroy Hills 680±55°C—7·4±1 kb; Kollaimalai area 680±40°C—8·6± 1 kb; Nilgiri Hills 680±90°C—6·6±0.8kb (upland massif) and 705±60°C—9·3±0.8 kb (northern margin); Bhavani Sagar area 650±50°C—7·2± 1 kb; Sargur-Mysore area 690±60°C—7·6 kb; Bangalore-Kunigal-Satnur area 760±50°C—6 kb. Except for the last subarea, the P-T model data reflect the conditions of a late annealing stage probably related to the retrogressive metamorphism. Conditions near the peak of granulite facies metamorphism (730–800°C—6·5–9·5 kb) are recorded by the core compositions of the minerals. Although a rather uniform cooling history of the main part of the charnockite-khondalite terrane is suggested from the temperature data, differential uplift of smaller blocks is indicated by the regional variation of the pressure data.

Zircon U–Pb ages of granulites from the Central Region of the Lewisian, northwestern Scotland

1972 ◽  
Vol 109 (3) ◽  
pp. 247-258 ◽  
Author(s):  
R. T. Pidgeon ◽  
D. R. Bowes
Keyword(s):  
Central Region ◽  
Granulite Facies ◽  
Reliable Estimate ◽  
High Grade ◽  
Granulite Facies Metamorphism ◽  
Size Fractions ◽  
Two Samples ◽  
Facies Metamorphism

SummaryThe overprinting of the high grade rocks of the Scourian episode, during the Inverian and Laxfordian episodes, has so far prevented a reliable estimate being made of the age of the Scourian granulite–facies metamorphism in the Central Region of the Lewisian of northwestern Scotland. In an attempt to solve this problem the U–Pb isotopic systems of zircons from two samples of hypersthene granulite from the Kylesku group have been examined. These zircons have discordant apparent ages complicating the interpretation of the results. However, by measuring a number of size fractions from each of the two zircon suites it has been possible to demonstrate that a major isotopic event or events took place approximately 2700 m.y. ago in these granulite–facies rocks. It has also been shown that the two discordance trends found for the two zircon populations can be explained in terms of episodic disturbances of the U–Pb isotopic systems at times which correspond to the known ages of ‘Laxfordian’ and ‘Caledonian’ events.

scholarly journals The mode of occurrence and petrogenesis of the sapphirine-bearing and associated rocks of West Greenland

1969 ◽  
Vol 24 ◽  
pp. 1-44
Author(s):  
R.K Herd ◽  
B.F Windley ◽  
M Ghisler
Keyword(s):  
Granulite Facies ◽  
Limited Range ◽  
Amphibolite Facies ◽  
Ultramafic Rocks ◽  
High Grade ◽  
Granulite Facies Metamorphism ◽  
Wide Range ◽  
Facies Metamorphism ◽  
Mode Of Occurrence ◽  
Anorthosite Complex

Seven occurrences of sapphirine-bearing rocks in the Fiskenæsset region are described in detail. They occur within a chromite-layered anorthosite complex that was metamorphosed by a hornblende-granulite facies metamorphism and then by a cordierite-amphibolite facies metamorphism. They were derived from spinel-layered ultramafic rocks that mostly occur as layers and lenses along the contacts between major metaanorthosite and pyribolite/amphibolite horizons within the complex. There are four types of sapphirine-bearing rocks - enstatite, pargasite, gedrite and phlogopite types, which represent a petrogenetic sequence involving increasing degrees of Si, Ca, K and H2O metasomatism related to shearing and deformation along meta-anorthosite-pyribolite junctions. Their relationship to associated non-sapphirine-bearing rocks is described. Brief mineralogical and petrological data are given for the principal minerals and rocks. In addition, two occurrences in the Sukkertoppen region are described in detail; these are also localised in meta-norite-ultramafic lenses in high grade gneisses. It is concluded that sapphirine is stable within a wide range af pressure and temperature conditions, but within a limited range of chemical environments.

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