High-temperature granulites

Hayob, Jodie L.; Essene, Eric J.; Ruíz, Joaquin

doi:10.1038/347133b0

Cited by 6 publications

(1 citation statement)

References 24 publications

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“…Rocks of the granulite facies series (higher-temperaturelower-pressure [HT-LP] metamorphism) are scavenged from the deeper parts of Mesozoic oceanic plateaus (e.g., Gregoire et al, 1994;Shafer et al, 2005) and occur in exposed middle to lower crust of young continental arcs (e.g., Lucassen and Franz, 1996). Although the interpretation is contentious, metapelitic xenoliths retrieved from Neogene volcanoes in central Mexico (Hayob et al, 1989(Hayob et al, , 1990 and at El Joyazo in southeast Spain (Cesare and Gomez-Pugnaire, 2001) have been argued to record evidence of Cenozoic G-UHTM, and evidence of melt-related processes in lower crustal garnet granulite xenoliths from Kilbourne Hole, Rio Grande Rift, suggests contemporary G-UHTM in the lower crust of rifts (Scherer et al, 1997).…”

Section: Contemporary Metamorphism (<200 Ma)mentioning

confidence: 99%

Characteristic thermal regimes of plate tectonics and their metamorphic imprint throughout Earth history: When did Earth first adopt a plate tectonics mode of behavior

Brown¹

2008

Special Paper 440: When Did Plate Tectonics Begin on Planet Earth?

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Where plates converge, one-sided subduction generates two contrasting thermal environments in the subduction zone (low dT/dP) and in the arc and subduction zone backarc or orogenic hinterland (high dT/dP). This duality of thermal regimes is the hallmark of modern plate tectonics, which is imprinted in the ancient rock record as penecontemporaneous metamorphic belts of two contrasting types, one characterized by higher-pressure-lower-temperature metamorphism and the other characterized by higher-temperature-lower-pressure metamorphism. Granulite facies ultrahigh-temperature metamorphism (G-UHTM) is documented in the rock record predominantly from the Neoarchean to the Cambrian, although it may be inferred at depth in some younger Phanerozoic orogenic systems. Medium-temperature eclogite-high-pressure granulite metamorphism (E-HPGM) also is fi rst recognized in the Neoarchean, although well-characterized examples are rare in the Neoarchean-to-Paleoproterozoic transition, and occurs at intervals throughout the Proterozoic and Paleozoic rock record. The fi rst appearance of E-HPGM belts in the rock record registers a change in geodynamics that generated sites of lower heat fl ow than previously seen, inferred to be associated with subduction-to-collision orogenesis. The appearance of coeval G-UHTM belts in the rock record registers contemporary sites of high heat fl ow, inferred to be similar to modern arcs, abd backarcs, or orogenic hinterlands, where more extreme temperatures were imposed on crustal rocks than previously recorded. Blueschists fi rst became evident in the Neoproterozoic rock record, and lawsonite blueschists, low-temperature eclogites (high-pressure metamorphism, HPM), and ultrahigh-pressure metamorphism (UHPM) characterized by coesite or diamond are predominantly Phanerozoic phenomena. HPM-UHPM registers low to intermediate apparent thermal gradients typically associated with modern subduction zones and the eduction of deeply subducted lithosphere, including the eduction of continental crust subducted during the early stage of the collision process in subduction-to-collision orogenesis. During the Phanerozoic, most UHPM belts have developed by closure of relatively short-lived ocean basins that opened due to rearrangement of the continental lithosphere within a continent-dominated hemisphere as Eurasia was formed from Rodinian orphans and joined with Gondwana in Pangea,

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Section: Contemporary Metamorphism (<200 Ma)mentioning

confidence: 99%

Characteristic thermal regimes of plate tectonics and their metamorphic imprint throughout Earth history: When did Earth first adopt a plate tectonics mode of behavior

Brown¹

2008

Special Paper 440: When Did Plate Tectonics Begin on Planet Earth?

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Ultra-high temperatures from oxygen isotope thermometry of a coesite-sanidine grospydite

Sharp

Essene

Smyth

1992

Contr. Mineral. and Petrol.

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The oxygen isotope compositions of coesite, sanidine, kyanite, clinopyroxene and garnet were measured in an ultra-high pressure-temperature grospydite from the Roberts Victor kimberlite, South Africa. The 5180 values (per mil v. SMOW) of each phase and (1 a) are as follows' coesite, 8.62 (0.31); sanidine, 8.31 (0.02); kyanite, 7.98 (0.08); pyroxene, 7.63 (0.11); garnet, 7.53 (0.03). In situ analyses of the coesite with the laser extraction system are 5180 =9.35 (0.08), n=4, demonstrating that the coesite is homogeneous. The coesite has partially inverted to polycrystalline quartz and the pyroxene is extensively altered during uplift. The larger scatter for the mineral separate coesite and pyroxene data may be due to partial reequilibration between the decompression-related breakdown products of these two phases. The anomalously high 5180 value of the grospydite 18 (5 Owhol .... k-7.7%0) is consistent with altered oceanic crust as a source rock. Temperature estimates from a linear regression of all the data to three different published calibrations correspond to an equilibrium temperature of 1310+80 ~ The calculated isotopic pressure effect is to lower these estimates by about 40 ~ at 40 kb. The estimated temperature based on A1-Si disorder in sanidine is 1200 + 100 ~ and that from Fe-Mg exchange thermometry between garnet and clinopyroxene is 1100 _+ 50 ~ Given the large errors associated with thermometry at such high temperatures, it is concluded that the xenolith equilibrated at 1200_+ 100 ~ Pressure estimates are 45 _+ 5 kb, based on dilution of the univariant equilibria albite =jadeite + coesite and 2 kyanite + 3 diopside = grossular + pyrope + 2 coesite. Zoning in the outer 20 gm of the feldspar from Ab0.8 to Ab16 indicates rapid decompression to 25 kb or less. The isotopic temperature estimates are the highest ever obtained and combined with the high degree of A1-Si disorder in sanidine require rapid cooling from ultra-high temperatures. It is inferred that the xenolith was sampled at the time of equilibration, providing a point on the upper Cretaceous geotherm in the mantle below South Africa.

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On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

Kelsey

Hand

2015

Geoscience Frontiers

367

285

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a b s t r a c tUltrahigh temperature (UHT) metamorphism is the most thermally extreme form of regional crustal metamorphism, with temperatures exceeding 900 C. UHT crustal metamorphism is recognised in more than 50 localities globally in the metamorphic rock record and is accepted as 'normal' in the spectrum of regional crustal processes. UHT metamorphism is typically identified on the basis of diagnostic mineral assemblages such as sapphirine þ quartz, orthopyroxene þ sillimanite AE quartz and osumilite in MgeAlrich rock compositions, now usually coupled with pseudosection-based thermobarometry using internally-consistent thermodynamic data sets and/or Al-in-Orthopyroxene and ternary feldspar thermobarometry. Significant progress in the understanding of regional UHT metamorphism in recent years includes: (1) development of a ferric iron activityecomposition thermodynamic model for sapphirine, allowing phase diagram calculations for oxidised rock compositions; (2) quantification of UHT conditions via trace element thermometry, with Zr-in-rutile more commonly recording higher temperatures than Ti-in-zircon. Rutile is likely to be stable at peak UHT conditions whereas zircon may only grow as UHT rocks are cooling. In addition, the extent to which Zr diffuses out of rutile is controlled by chemical communication with zircon; (3) more fully recognising and utilising temperature-dependent thermal properties of the crust, and the possible range of heat sources causing metamorphism in geodynamic modelling studies; (4) recognising that crust partially melted either in a previous event or earlier in a long-duration event has greater capacity than fertile, unmelted crust to achieve UHT conditions due to the heat energy consumed by partial melting reactions; (5) more strongly linking UePb geochronological data from zircon and monazite to PeT points or path segments through using Y þ REE partitioning between accessory and major phases, as well as phase diagrams incorporating Zr and REE; and (6) improved insight into the settings and factors responsible for UHT metamorphism via geodynamic forward models. These models suggest that regional UHT metamorphism is, principally, geodynamically related to subduction, coupled with elevated crustal radiogenic heat generation rates.Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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High-temperature granulites

Cited by 6 publications

References 24 publications

Characteristic thermal regimes of plate tectonics and their metamorphic imprint throughout Earth history: When did Earth first adopt a plate tectonics mode of behavior

Characteristic thermal regimes of plate tectonics and their metamorphic imprint throughout Earth history: When did Earth first adopt a plate tectonics mode of behavior

Ultra-high temperatures from oxygen isotope thermometry of a coesite-sanidine grospydite

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

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