Journal of Petrology Advance Access originally published online on February 4, 2005
Journal of Petrology 2005 46(6):1085-1119; doi:10.1093/petrology/egi011
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Mesoproterozoic Reworking of Palaeoproterozoic Ultrahigh-temperature Granulites in the Central Indian Tectonic Zone and its Implications
1 DEPARTMENT OF GEOLOGY AND GEOPHYSICS, INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR-721 302, INDIA
2 MINERALOGISCH–PETROLOGISCHES INSTITUT, DER UNIVERSITÄT BONN, POPPELSDORFER SCHLOß, D-53115 BONN, GERMANY
RECEIVED OCTOBER 4, 2003; ACCEPTED DECEMBER 14, 2004
In the southern periphery of the Sausar Mobile Belt (SMB), the southern component of the Central Indian Tectonic Zone (CITZ), a suite of felsic and aluminous granulites, intruded by gabbro, noritic gabbro, norite and orthopyroxenite, records the polymetamorphic evolution of the CITZ. Using sequences of prograde, peak and retrograde reaction textures, mineral chemistry, geothermobarometric results and petrogenetic grid considerations from the felsic and the aluminous granulites and applying metamorphosed mafic dyke markers and geochronological constraints, two temporally unrelated granulite-facies tectonothermal events of Pre-Grenvillian age have been established. The first event caused ultrahigh-temperature (UHT) metamorphism (M1) (T 
950°C) at relatively deeper crustal levels (P 9 kbar) and a subsequent post-peak near-isobaric cooling P–T history (M2). M1 caused pervasive biotite-dehydration melting, producing garnet–orthopyroxene and garnet–rutile and sapphirine–spinel-bearing incongruent solid assemblages in felsic and aluminous granulites, respectively. During M2, garnet–corundum and later spinel–sillimanite–biotite assemblages were produced by reacting sapphirine–spinel–sillimanite and rehydration of garnet–corundum assemblages, respectively. Applying electron microprobe (EMP) dating techniques to monazites included in M1 garnet or occurring in low-strain domains in the felsic granulites, the UHT metamorphism is dated at 2040–2090 Ma. Based on the deep crustal heating–cooling P–T trajectory, the authors infer an overall counterclockwise P–T path for this UHT event. During the second granulite event, the Palaeoproterozoic granulites experienced crustal attenuation to 6·4 kbar at T 675°C during M3 and subsequent near-isothermal loading to 8 kbar during M4. In the felsic granulites, the former is marked by decomposition of M1 garnet to orthopyroxene–plagioclase symplectites. During M4, there was renewed growth of garnet–quartz symplectites in the felsic granulites, replacing the M3 mineral assemblage and also the appearance of coronal garnet–quartz–clinopyroxene assemblages in metamorphosed mafic dykes. Using monazites from metamorphic overgrowths and metamorphic recrystallization domains from the felsic granulite, the M4 metamorphism is dated at 1525–1450 Ma. Using geochronological and metamorphic constraints, the authors interpret the M3–M4 stages to be part of the same Mesoproterozoic tectonothermal event. The result provides the first documentation of UHT metamorphism and Palaeo- and Mesoproterozoic metamorphic processes in the CITZ. On a broader scale, the findings are also consistent with the current prediction that isobarically cooled granulites require a separate orogeny for their exhumation.
KEY WORDS: Central Indian Tectonic Zone; UHT metamorphism; counterclockwise P–T path; monazite chemical dating
* Corresponding author. E-mail: santanu{at}gg.iitkgp.ernet.in
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  S. PATRANABIS-DEB, J. SCHIEBER, and A. BASU Almandine garnet phenocrysts in a ~ 1 Ga rhyolitic tuff from central India Geological Magazine, January 1, 2009; 146(1): 133 - 143. [Abstract] [Full Text] [PDF]
|
|