Palaeoproterozoic ancestry of Pan-African high-grade granitoids in southernmost India: Implications for Gondwana reconstructions

Kröner, Alfred; Santosh, M.; Hegner, E.; Shaji, E.; Geng, Haifeng; Wong, Jean; Xie, Hanqiang; Wan, Yusheng; Shang, C. K.; Liu, D.; Sun, Min; Nandakumar, V.

doi:10.1016/j.gr.2014.07.001

Cited by 65 publications

(62 citation statements)

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“…Two examples of this behaviour are illustrated in Figure 6. A compilation of zircon, and monazite, ages for G-UHT metamorphism in the Trivandrum Block of southern India (Whitehouse et al, 2014;Harley and Nandakumar, 2014;Taylor et al, 2014;Kröner et al, 2015) shows not only that the metamorphism was long-lived, or 'slow', but also that the accessory minerals grew over several time periods in the overall 580-515 Ma age range. Anatectic zircons are reported to have formed at 575, 560, 545, 535, and even 520 Ma, with some localities preserving more than one age.…”

Section: Constraining Temperature and Time In Uht Metamorphismmentioning

confidence: 99%

A matter of time: The importance of the duration of UHT metamorphism

Harley

2016

Journal of Mineralogical and Petrological Sciences

134

110

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The duration of granulite (G) and ultra-high temperature (UHT) conditions in regional metamorphism is critical to arguments regarding the tectonic settings of granulites and their relationships to Supercontinent assembly. Analysis of zircon geochronology integrated with trace element (REE) constraints on the timing of zircon growth or modification and evidence for metamorphic temperatures from Ti-in-zircon reveals that zircon can form episodically at or near the metamorphic peak in long-lived UHT granulites. This reflects the segregation, transfer and stagnation or trapping of melts which leads to local melt-rock interactions that promotes zircon crystallisation. In contrast, although rutile can retain UHT information in short duration ('fast') G-UHT terrains it is afflicted by Zr loss in long duration ('slow') terrains and yields temperatures significantly lower than those preserved by zircons formed in the same G-UHT events. An assessment of the age-duration evidence from several well-documented G-UHT terrains reveals that most are 'slow', having durations of UHT, Δt 900 , in the range 30-100 Myr. Some UHT terrains previously considered to be short-lived (Δt 900 < 10 Myr) have longer durations of UHT in the light of recent geochronology and hence are also classed as 'slow'. Of the models proposed to account for UHT metamorphism, the 'large hot orogen' (LHO) model for collisional orogeny provides the best setting for the formation of such 'slow' UHT granulites. LHO models can account not only for the P-T paths, which can range from UHT with near-isothermal decompression (UHT-ITD) through to decompression-cooling and UHT followed by near-isobaric cooling (UHT-IBC), but also for residence times under UHT conditions. The Napier Complex, the Earth's premier UHT terrain, probably formed as trapped deep crust in the hot underbelly of a late-Archaean LHO. Shorter duration UHT and near-UHT granulites also exist, mostly with Δt 900 less than 10 Myr. A number of these are likely to have formed as a consequence of severe lithospheric thinning and crustal extension accompanied by voluminous magmatism, which could occur in arc and back-arc settings affected by subduction roll-back or, as advocated by previous workers, continental arcs undergoing extension. However, attaining long-lived UHT conditions in these settings is unlikely unless the crust has inherently high radioactive heat production in addition to the transient heat added during extension and magmatism.

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Section: Constraining Temperature and Time In Uht Metamorphismmentioning

confidence: 99%

A matter of time: The importance of the duration of UHT metamorphism

Harley

2016

Journal of Mineralogical and Petrological Sciences

134

110

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“…Other igneous protoliths include~2.0, 1.7-1.6, and 1.0 Ga granite in the Nagercoil and northeastern and southern Madurai blocks of India (Plavsa et al, 2012;Brandt et al, 2014;Kröner et al, 2015), local 2.2-1.8 and~1.0 Ga mafic and felsic rocks in south-central Madagascar (Tucker et al, 2011b), and 0.94-0.90 Ga alkali granite and anorthosite in southern Madagascar (Boger et al, 2015). Most metasedimentary units in Madagascar and southern India contain abundant 2.7-2.4 and 2.2-1.8 Ga detrital zircons (Cox et al, 1998(Cox et al, , 2004Fitzsimons and Hulscher, 2005;Collins et al, 2007b;De Waele et al, 2011;Collins et al, 2012;Boger et al, 2014;Plavsa et al, 2014), but 1.1-0.9 Ga detritus dominates the Ikalamavony Domain of Madagascar (Tucker et al, 2011b) and southern Madurai Block and Achankovil Zone of India , and detritus in the Malagasy suture can have a mix of age populations including 3.3-3.1, 2.7-2.4, 2.2-1.8 and 0.84-0.70 Ga (Collins et al, 2003;Key et al, 2011).…”

Section: Reworked Crust Of the Southern East African Orogenmentioning

confidence: 99%

Pan–African granulites of Madagascar and southern India: Gondwana assembly and parallels with modern Tibet

Fitzsimons

2016

Journal of Mineralogical and Petrological Sciences

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Granulites of the southern East African Orogen formed by continental collision during Gondwana assembly. The highest metamorphic gradients of 25-50°C km −1 were attained at 0.58-0.53 Ga in a microcontinental block that was sandwiched between two collisional sutures and is now exposed in Madagascar and southern India. The 50 Myr duration of extreme pressure-temperature (P-T) conditions and lack of coeval mantle magmatism suggest that metamorphism was driven by radiogenic heat accumulation beneath a long-lived orogenic plateau. Bounding sutures most likely record transfer of this microcontinent across the Neoproterozoic Mozambique Ocean, analogous to Gondwanan terranes that crossed Tethys before final India-Asia collision and, like Tibet, these sutures mark the edges of a plateau that formed following terminal ocean closure and collision. Both sutures record moderate metamorphic gradients of 15-25°C km −1 but with quite different ages. Metamorphism along the western suture at 0.65-0.61 Ga followed the end of magmatism in an adjacent 0.85-0.65 Ga ocean-arc terrane. It has an anti-clockwise P-T path that reflects preferential thickening of the hot arc during early stages of collision, and dates ocean closure at the western suture. Metamorphism along the eastern suture at 0.53-0.51 Ga has a clockwise P-T path and is widely assumed to date terminal collision in the East African Orogen. However, this event was coeval with rapid exhumation of granulites in the adjacent plateau and is more likely to reflect reactivation of a much older eastern suture during plateau collapse. Great care should be taken when using metamorphism to date ocean closure in ancient orogens. Rocks with hot metamorphic gradients give poor age constraints on initial collision because peak T is attained >50 Myr after ocean closure if radioactivity is a major part of the heat budget. Suture zone rocks with moderate metamorphic gradients can provide more reliable estimates for the time of ocean closure but are also prone to later reactivation in orogens with protracted histories.

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“…The SGT comprises predominantly of charnockite and orthogneisses defining the crystalline basement, together with migmatites, metasediments, granitoids, and mafic and ultramafic rocks. The terrain is divided into three discrete tectonic blocks: the Northern Granulite Block (comprising several Mesoarchean to Neoarchean crustal blocks; Santosh et al, 2014Santosh et al, , 2015, the Madurai Block (a collage of Neoarchean to Neoproterozoic crustal blocks; Plavsa et al, 2012;Clark et al, 2014), the Trivandrum Block and the Nagercoil Block (Paleoproterozoic to late Neoproterozoic units; Kroner et al, 2014), separated by two major collision zones: the Cauvery Suture/Shear Zone (CSZ) in the north (Fig. 1) and the Achankovil Shear Zone in the south.…”

Section: Introductionmentioning

confidence: 99%