High-pressure granulites at the dawn of the Proterozoic

Anderson, J.R.; Payne, Justin L.; Kelsey, David E.; Hand, Martin; Collins, Alan S.; Santosh, M.

doi:10.1130/g32854.1

Cited by 84 publications

(39 citation statements)

References 25 publications

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“…Eclogites–high‐ P granulites reported from various Paleoproterozoic orogenic belts (e.g. Möller et al ., ; Anderson et al ., ) reflect a broadening range of tectono‐metamorphic environments during this period (Brown, ). Harley () showed that the metamorphic record of Proterozoic granulites requires multiple geodynamic settings.…”

Section: Discussionmentioning

confidence: 99%

Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Block

Ganne

Baratoux

et al. 2015

Journal Metamorphic Geology

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New petrological and geochronological data are presented on high-grade ortho-and paragneisses from northwestern Ghana, forming part of the Paleoproterozoic (2.25-2.00 Ga) West African Craton. The study area is located in the interference zone between N-S and NE-SW-trending craton-scale shear zones, formed during the Eburnean orogeny (2.15-2.00 Ga). High-grade metamorphic domains are separated from low-grade greenstone belts by high-strain zones, including early thrusts, extensional detachments and late-stage strike-slip shear zones. Paragneisses sporadically preserve high-pressure, low-temperature (HP-LT) relicts, formed at the transition between the blueschist facies and the epidote-amphibolite sub-facies (10.0-14.0 kbar, 520-600°C), and represent a low (~15°C km À1 ) apparent geothermal gradient. Migmatites record metamorphic conditions at the amphibolite-granulite facies transition. They reveal a clockwise pressure-temperature-time (P-T-t) path characterized by melting at pressures over 10.0 kbar, followed by decompression and heating to peak temperatures of 750°C at 5.0-8.0 kbar, which fit a 30°C km À1 apparent geotherm. A regional amphibolite facies metamorphic overprint is recorded by rocks that followed a clockwise P-T-t path, characterized by peak metamorphic conditions of 7.0-10.0 kbar at 550-680°C, which match a 20-25°C km À1 apparent geotherm. These P-T conditions were reached after prograde burial and heating for some rock units, and after decompression and heating for others. The timing of anatexis and of the amphibolite facies metamorphic overprint is constrained by in-situ U-Pb dating of monazite crystallization at 2138 AE 7 and 2130 AE 7 Ma respectively. The new data set challenges the interpretation that metamorphic breaks in the West African Craton are due to diachronous Birimian 'basins' overlying a gneissic basement. It suggests that the lower crust was exhumed along reverse, normal and transcurrent shear zones and juxtaposed against shallow crustal slices during the Eburnean orogeny. The craton in NW Ghana is made of distinct fragments with contrasting tectono-metamorphic histories. The range of metamorphic conditions and the sharp lateral metamorphic gradients are inconsistent with 'hot orogeny' models proposed for many Precambrian provinces. These findings shed new light on the geodynamic setting of craton assembly and stabilization in the Paleoproterozoic. It is suggested that the metamorphic record of the West African Craton is characteristic of Paleoproterozoic plate tectonics and illustrates a transition between Archean and Phanerozoic orogens.

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Section: Discussionmentioning

confidence: 99%

Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Block

Ganne

Baratoux

et al. 2015

Journal Metamorphic Geology

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“…There have been a few reports of the early-to mid-Neoproterozoic ages now from the Madurai Block (Sato et al 2011;Teale et al 2011;Anderson et al 2012;Brandt et al 2014), since Santosh et al (2009) made the compilation indicating a gap between early-Paleoproterozoic and late-Neoproterozoic (see figure 7 of Santosh et al 2009). The available geochronological dataset indicates significant events during early to mid-Neoproterozoic period within the Madurai Block, though their importance in the broader framework of Wilson cycle, as proposed by Santosh et al (2009) is yet to be established.…”

Section: Geological Settingmentioning

confidence: 95%

Rb–Sr and Sm–Nd study of granite–charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

2016

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Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb-Sr biotite and Sm-Nd whole-rock isochron ages indicate a regional uplift and cooling at ∼550 Ma. The initial Nd isotope ratios (ε t Nd = −20 to −22) and Nd depleted-mantle model ages (T DM = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (ε t Nd = −29 and T DM = >3.2 Ga). The Rb-Sr whole-rock data and initial Sr-Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an 'apparent whole-rock isochron'. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean-Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which 'prepared' the residual crust to sustain the high P -T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.

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“…Whereas the minimum peaktemperature conditions of~810°C at~0.94 GPa for the Majorqaq Belt yield an apparent thermal gradient of~860°C/GPa, which represents conditions typical of crustal thickening during orogenesis (Brown, 2007). A Neoarchaean shift in tectonic regimes has been evidenced by an increase in observed continental crustal thickness ≥ 50 km (Anderson et al, 2012;Moyen et al, 2006) and recycling of crustal derived material into the upper mantle (Keller and Schoene, 2012;Naeraa et al, 2012;Shirey and Richardson, 2011;Van Kranendonk, 2011), and the onset of global kimberlite magmatism (Tappe et al, 2013;Tappe et al, 2014). On the basis of the chronologic evidence presented here, we propose that the high-pressure amphibolite-facies metamorphism in the Majorqaq Belt records evidence for a Neoarchaean orogeny.…”

Section: Neoarchaean Orogenesismentioning

confidence: 97%

The Majorqaq Belt: A record of Neoarchaean orogenesis during final assembly of the North Atlantic Craton, southern West Greenland

Dyck

Reno

Kokfelt

2015

Lithos

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High-pressure granulites at the dawn of the Proterozoic

Cited by 84 publications

References 25 publications

Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Petrological and geochronological constraints on lower crust exhumation during Paleoproterozoic (Eburnean) orogeny, NW Ghana, West African Craton

Rb–Sr and Sm–Nd study of granite–charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

The Majorqaq Belt: A record of Neoarchaean orogenesis during final assembly of the North Atlantic Craton, southern West Greenland

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