Post-orogenic thermal evolution of newborn Archean continents

Jaupart, Claude; Mareschal, Jean‐Claude

doi:10.1016/j.epsl.2015.09.047

Cited by 18 publications

(11 citation statements)

References 58 publications

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“…Blueschists are initially stable in the newly formed lithosphere but will slowly heat up during postcollisional orogenic collapse. Because the thickened crust slowly relaxes and thins in postcollisional conditions (37), it takes 10 to 30 Ma for the lower block to achieve thermal equilibrium (38), which agrees well with the timing of postcollisional volcanism, which first occurs after this period. However, the P-T-t path consists mostly of heating with a slight reduction in pressure due to extension and to erosion of the continent above it during postcollisional relaxation.…”

Section: Multistage Evolution Of Elevated Th/la In Alpine-himalayan Vsupporting

confidence: 74%

Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere

et al. 2021

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Potassium-rich volcanism occurring throughout the Alpine-Himalayan belt from Spain to Tibet is characterized by unusually high Th/La ratios, for which several hypotheses have brought no convincing solution. Here, we combine geochemical datasets from potassic postcollisional volcanic rocks and lawsonite blueschists to explain the high Th/La. Source regions of the volcanic melts consist of imbricated packages of blueschist facies mélanges and depleted peridotites, constituting a new mantle lithosphere formed only 20 to 50 million years earlier during the accretionary convergence of small continental blocks and oceans. This takes place entirely at shallow depths (<80 km) without any deep subduction of continental materials. High Th/La in potassic rocks may indicate shallow sources in accretionary settings even where later obscured by continental collision as in Tibet. This mechanism is consistent with a temporal trend in Th/La in potassic postcollisional magmas: The high Th/La signature first becomes prominent in the Phanerozoic, when blueschists became widespread.

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Section: Multistage Evolution Of Elevated Th/la In Alpine-himalayan Vsupporting

confidence: 74%

Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere

et al. 2021

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“…Noting that the concentrations of the heat-producing elements in fine-grained metasedimentary rocks have not decreased since the Paleoproterozoic (Taylor and McLennan, 1985) and radiogenic heat production from granites has remained constant through time (Artemieva et al , 2017), but mantle potential temperatures have decreased since the Neoarchean (Herzberg et al , 2010), it might be expected that higher metamorphic temperatures would have been achieved in the Neoarchean compared with the Phanerozoic. However, maximum temperatures of crustal metamorphism are probably buffered by melting (Stüwe, 1995; Schorn et al , 2018), consistent with the postulate by Jaupart and Mareschal (2015) and Jaupart et al (2016) that the post-orogenic thermal evolution and stabilisation of Archean cratons occurred by intracrustal differentiation driven by high radiogenic heat production that raised lower crustal temperatures to 800–900°C, but without significant crustal thickening. Also, if we accept that the increase in pressure of intermediate T/P metamorphism indicates a change in the style of collisional orogenesis with decreasing age, then the absence of significant secular variation in the mean temperature and thermobaric ratios of high T/P metamorphism requires explanation.…”

Section: The Metamorphic Record and Time's Arrowsupporting

confidence: 71%

Time's arrow, time's cycle: Granulite metamorphism and geodynamics

Brown

Johnson

2019

MinMag

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Although the thermal evolution of the mantle before c. 3.0 Ga remains unclear, since c. 3.0 Ga secular cooling has dominated over heat production—this is time's arrow. By contrast, the thermal history of the crust, which is preserved in the record of metamorphism, is more complex. Heat to drive metamorphism is generated by radioactive decay and viscous dissipation, and is augmented by the influx of heat from the mantle. Notwithstanding that reliable data are sparse before the Neoarchean, we use a dataset of temperature (T), pressure (P) and thermobaric ratio (T/P at the metamorphic ‘peak’), and age of metamorphism (t, the timing of the metamorphic ‘peak’) for rocks from 564 localities ranging in age from the Cenozoic to the Eoarchean eras to interrogate the crustal record of metamorphism as a proxy for the heat budget of the crust through time. On the basis of T/P, metamorphic rocks are classified into three natural groups: high T/P type (T/P >775°C/GPa, mean T/P ~1105°C/GPa), including common and ultrahigh-temperature granulites, intermediate T/P type (T/P between 775 and 375°C/GPa, mean T/P ~575°C/GPa), including high-pressure granulites and medium- and high-temperature eclogites, and low T/P type (T/P <375°C/GPa, mean T/P ~255°C/GPa), including blueschists, low-temperature eclogites and ultrahigh-pressure metamorphic rocks. A monotonic increase in the P of intermediate T/P metamorphism from the Neoarchean to the Neoproterozoic reflects strengthening of the lithosphere during secular cooling of the mantle—this is also time's arrow. However, temporal variation in the P of intermediate T/P metamorphism and in the moving means of T and T/P of high T/P metamorphism, combined with the clustered age distribution, demonstrate the cyclicity of collisional orogenesis and cyclic variations in the heat budget of the crust superimposed on secular cooling since c. 3.0 Ga—this is time's cycle. A first cycle began with the widespread appearance/survival of intermediate T/P and high T/P metamorphism in the Neoarchean rock record coeval with amalgamation of dispersed blocks of lithosphere to form protocontinents. This cycle was terminated by the fragmentation of the protocontinents into cratons in the early Paleoproterozoic, which signalled the start of a new cycle. The second cycle continued with the progressive amalgamation of the cratons into the supercontinent Columbia and extended until the breakup of the supercontinent Rodinia in the Neoproterozoic. This cycle represented a period of relative tectonic and environmental stability, and perhaps reduced subduction during at least part of the cycle. During most of the Proterozoic the moving means for both T and T/P of high T/P metamorphism exceeded the arithmetic means, reflecting insulation of the mantle beneath the quasi-integrated lithosphere of Columbia and, after a limited reorganisation, Rodinia. The third cycle began with the steep decline in thermobaric ratios of high T/P metamorphism to their lowest value, synchronous with the breakup of Rodinia and the formation of Pannotia, and the widespread appearance/preservation of low T/P metamorphism in the rock record. The thermobaric ratios for high T/P metamorphism rise to another peak associated with the Pan-African event, again reflecting insulation of the mantle. The subsequent steep decline in thermobaric ratios of high T/P metamorphism associated with the breakup of Pangea at c. 0.175 Ga may indicate the start of a fourth cycle. The limited occurrence of high and intermediate T/P metamorphism before the Neoarchean suggests either that suitable tectonic environments to generate these types of metamorphism were not widely available before then or that the rate of survival was low. We interpret the first cycle to record stabilisation of subduction and the emergence of a network of plate boundaries in a plate tectonics regime once the balance between heat production and heat loss changed in favour of secular cooling, possibly as early as c. 3.0 Ga in some areas. This is inferred to have been a globally linked system by the early Paleoproterozoic, but whether it remained continuous to the present is unclear. The second cycle was characterised by stability from the formation of Columbia to the breakup of Rodinia, generating higher than average T and T/P of high T/P metamorphism. The third cycle reflects colder collisional orogenesis and deep subduction of the continental crust, features that are characteristic of modern plate tectonics, which became possible once the average temperature of the asthenospheric mantle had declined to <100°C warmer than the present day after c. 1.0 Ga.

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“…c Q adjusted to value at 300 MPa where pressure-dependent activation volume terms are provided. d A has been adjusted for dry conditions using results of Barbery (2017) Jaupart & Mareschal, 2015) to the mass of Venus results in a steady state conductive geotherm of 25 K/km (after Solomon & Head, 1982;D. L. Turcotte, 1995).…”

Section: Strain Rate and Geothermal Gradientmentioning

confidence: 99%

Felsic Tesserae on Venus Permitted by Lithospheric Deformation Models

et al. 2021

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Tessera terrain, a major tectonic unit on Venus, comprises ∼8% of the planet's surface and occurs as large (>10 3 km across) high-standing (∼1-4 km above mean planetary radius) plateaus and small (<100 km across) outcrops scattered among the global volcanic plains (Ivanov & Head, 1996). Stratigraphic studies of tesserae establish that they are embayed by, and thus older than, volcanic plains that cover most of the planet's surface (e.g., Ivanov & Head, 1996, in agreement with a tessera crater retention age of 1 (Strom et al., 1994) to 1.4 (Ivanov & Basilevsky, 1993) times the average planetary surface age of ∼300 Ma (Strom et al., 1994) to ∼1 Ga (McKinnon et al., 1997). Tesserae contain the oldest rocks on the surface of Venus and are the only rock record of the planet's history prior to production of the presumably basaltic plains. The composition of tesserae remains unknown. Their plateau shape (Nikolayeva, 1990), dielectric permittivity (Kreslavsky et al., 2000), and infrared emissivity (M. S. Gilmore et al., 2015;Hashimoto et al., 2008) suggest that tesserae are more silica rich than the plains. A felsic tesserae composition would require formation in an extinct era via either voluminous partial melting of basalt or crustal recycling in the presence of abundant water (M.

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Post-orogenic thermal evolution of newborn Archean continents

Cited by 18 publications

References 58 publications

Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere

Origin of potassic postcollisional volcanic rocks in young, shallow, blueschist-rich lithosphere

Time's arrow, time's cycle: Granulite metamorphism and geodynamics

Felsic Tesserae on Venus Permitted by Lithospheric Deformation Models

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