An extensive record of orogenesis recorded in a Madagascar granulite

Horton, Forrest; Holder, Robert; Swindle, Carl

doi:10.1111/jmg.12628

Cited by 9 publications

(4 citation statements)

References 76 publications

(147 reference statements)

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“…Similar clockwise P-T evolution paths are postulated for UHT metamorphism in Antarctica (Elvevold et al, 2020;Harley, 1998bHarley, , 2003Kawakami & Motoyoshi, 2004;Kelsey et al, 2007;Takamura et al, 2020) and Madagascar (e.g. Holder et al, 2018;Horton et al, 2021;Jöns & Schenk, 2011) as well. Our data from the semipelites and charnockites of the MB suggest a clockwise P-T evolution with an inferred peak at f).…”

Section: Heat Source and Geodynamic Implicationssupporting

confidence: 60%

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

Tiwari,

Sarkar,

Karmakar

et al. 2023

Journal Metamorphic Geology

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The Granulite Terrane of Southern India is a collage of Mesoarchean–Neoproterozoic crustal blocks that underwent high‐grade metamorphism associated with the final assembly of the Gondwana supercontinent during late Neoproterozoic–Cambrian. Here, we investigate the charnockites and associated sapphirine‐bearing semipelitic granulites from the eastern part of the Madurai Block (MB). We present new petrographic, mineral chemistry, and geochronological data to constrain the P–T–t evolution of the block and unravel the timescale and source of heat for the ultrahigh‐temperature metamorphism. Both the rock types contain coarse‐grained porphyroblastic garnet and orthopyroxene, yielding peak P–T conditions of 950 ± 30°C at 10.5 ± 0.8 kbar and 970 ± 40°C at 10 ± 0.5 kbar for semipelite and charnockite, respectively, using conventional thermobarometry. Peak ultrahigh temperatures are further supported by high Al content in the orthopyroxene (8.78 wt% Al2O3) coexisting with garnet (XMg: up to 0.57) and feldspar thermometry of the mesoperthites and antiperthites in the semipelite, yielding 950–980°C at 10 kbar. Subsequent decompression has led to the formation of coronal orthopyroxene3 + plagioclase3 in the charnockite and symplectic orthopyroxene3 + cordierite ± sapphirine ± plagioclase3 in the semipelite, yielding P–T range of 950–850°C and 9.5–6.8 kbar for semipelites and 950–820°C and 8–6.5 kbar for charnockite. Based on the obtained P–T estimates, preserved reaction textures, and phase equilibria modelling in the MnNCKFMASHTO system, a clockwise P–T evolution with isothermal decompression followed by cooling is inferred for both the rock types.Texturally constrained in situ monazite dating and rare earth element (REE) patterns show that the core of matrix monazite having low‐Th, Y, and extreme heavy rare earth element (HREE) depletion, yielding weighted mean ages of 582 ± 12 and 590 ± 22 Ma for semipelite and charnockite, respectively, dates the prograde evolution. The mantle of the matrix monazite in semipelite and comparable rim in charnockite, having relative Th‐enrichment compared to the core, yielding weighted mean ages of 552 ± 9 and 557 ± 13 Ma, respectively, dates extensive dissolution–reprecipitation from the melt at the peak stage. The relatively Th‐ and Y‐rich and moderately HREE‐depleted rim of matrix monazite in the semipelite, yielding weighted age of 516 ± 6 Ma, date initial garnet breakdown during post‐peak melt crystallization. By contrast, compositionally homogenous HREE + Y‐enriched monazite in the symplectite and retrograde monazites yielding weighted mean ages of 487 ± 47 Ma for semipelites and 508 ± 19 Ma for charnockites dates extensive garnet breakdown during final stages of melt crystallization and subsequent cooling. Our findings point to collision initiation at ~590 Ma, with the peak conditions attained at ~550 Ma followed by extensional collapse at ~510–490 Ma, resulting in rapid exhumation of lower crustal rocks to mid‐crustal levels under sustained ultrahigh‐temperature (UHT) conditions, followed by cooling to reach a stable geotherm. Our results suggest a long‐lived hot orogeny in the MB, where the UHT conditions were sustained for at least 40 MYr. The UHT conditions were most likely attained in the core of a long‐lived hot orogen by the combined effect of conductive heating through radioactive decay and mantle heat supply, with the former being the primary driver.

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Section: Heat Source and Geodynamic Implicationssupporting

confidence: 60%

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

Tiwari,

Sarkar,

Karmakar

et al. 2023

Journal Metamorphic Geology

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“…Both samples are derived from a high-grade metamorphic domain that reached 7-9 kbar and 800-950 • C [73,74] as it formed during the Ediacaran to early Cambrian assembly of East and West Gondwana [74][75][76]. Most studies suggest that the high-grade metamorphism and associated magmatism in southern Madagascar ceased at ~520-500 Ma [74][75][76][77][78][79][80][81][82][83], and that rocks in the area cooled below ~400 • C between ~530-490 Ma [75,83,84], below ~300 • C between ~500-300 Ma [83][84][85][86] and through ~150-60 • C between ~400-200 Ma [84,85,87,88]. Published 40 Ar/ 39 Ar and K-Ca dates of gem-quality K-feldspar from the Itrongay locality span from ~477 to ~375 Ma [64,[89][90][91], which we previously interpreted to mostly reflect crystallisation age variations [64].…”

Section: Methodsmentioning

confidence: 99%

Inclusions of Amorphous and Crystalline SiO2 in Minerals from Itrongay (Madagascar) and Other Evidence for the Natural Occurrence of Hydrosilicate Fluids

2022

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Experimental studies increasingly often report low-temperature (200–800 °C) and low-pressure (0.05–3 kbar) hydrosilicate fluids with >40 wt.% of SiO2 and >10 wt.% of H2O. Compositionally similar fluids were long suggested to potentially exist in natural systems such as pegmatites and hydrothermal veins. However, they are rarely invoked in recent petrogenetic models, perhaps because of the scarcity of direct evidence for their natural occurrence. Here we review such evidence from previous works and add to this by documenting inclusions of hydrosilicate fluids in quartz and feldspar from Itrongay. The latter comprise opal-A, opal-CT, moganite and quartz inclusions that frequently contain H2O and have negative crystal shapes. They coexist with inclusions of CO2- and H2O-rich fluids and complex polycrystalline inclusions containing chlorides, sulphates, carbonates, arsenates, oxides, hydroxides and silicates, which we interpret as remnants of saline liquids. Collectively, previous studies and our new results indicate that hydrosilicate fluids may be common in the Earth’s crust, although their tendency to transform into quartz upon cooling and exhumation renders them difficult to recognise. These data warrant more comprehensive research into the nature of such hydrosilicate fluids and their distribution across a wide range of pressure and temperature conditions and geological systems.

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“…In central Madagascar, U-Pb metamorphic ages obtained from zircon rims range from 670 to 540 Ma 57 . In southern Madagascar, high-temperature and ultra-high temperature (UHTM) metamorphism took place between 580 and 510 Ma based on ages from metamorphic monazite in metapelite, and igneous zircons, and monazite in syn-and post-tectonic granitoids 57,[63][64][65][66][67] (Fig. 2).…”

Section: The Mozambique Ocean and The East African Orogenmentioning

confidence: 99%

Neoproterozoic reorganization of the Circum- Mozambique orogens and growth of megacontinent Gondwana

Wang

Jing

Meert

2023

Commun Earth Environ

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The serpentine orogenic belts that formed during the Neoproterozoic assembly of Gondwana resulted in geodynamic changes on the planet in advance of the Cambrian radiation. The details of Gondwana assembly associated with the closure of the Mozambique Ocean are enigmatic. We compile published geological and paleomagnetic data to argue that the Tarim block was associated with the Azania and Afif–Abas–Lhasa terranes and they were the locus of long-lived Andean-type subduction during the ~900–650 Ma interval. Our model suggests a subduction system reorganization between 750-720 Ma, which resulted in two distinct phases of Mozambique ocean evolution. Between 870-750 Ma, a N-S oriented subduction system marks the locus of ocean crust consumption driven by the extension of the Mozambique Ocean. Beginning ~720 Ma, a newly developed ~E-W oriented subduction system began to consume the Mozambique Ocean and led to the assembly of eastern Gondwana. Our new reconstruction uses true polar wander to constrain the relative paleolongitude of Tarim, South China and West Africa. In this scenario, the closure of the Mozambique Ocean and formation of Gondwana was orthogonal to the preceding supercontinent Rodinia.

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An extensive record of orogenesis recorded in a Madagascar granulite

Cited by 9 publications

References 76 publications

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

Inclusions of Amorphous and Crystalline SiO2 in Minerals from Itrongay (Madagascar) and Other Evidence for the Natural Occurrence of Hydrosilicate Fluids

Neoproterozoic reorganization of the Circum- Mozambique orogens and growth of megacontinent Gondwana

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