Characteristics of, and a Tectonic Model for, Ultrahigh-Pressure Metamorphism in the Overriding Plate of the Caledonian Orogen

Gilotti, Jane A.; McClelland, William C.

doi:10.2747/0020-6814.49.9.777

Cited by 57 publications

(51 citation statements)

References 90 publications

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“…Coesite inclusions in zircon are documented in eclogite and felsic host gneiss on REI; U-Pb zircon geochronology by ion probe on the exact domains that contain coesite shows that UHP metamorphism occurred from 365 to 350 Ma (McClelland et al, 2006), much later than the HP metamorphism. UHP metamorphism late in the collision in the overriding plate may have formed by intracontinental subduction, where lithosphere-breaking strike-slip faults subjected to continued plate convergence brought the already thickened Laurentian crust down to mantle depths (Gilotti and McClelland, 2007).…”

Section: Geologic Settingmentioning

confidence: 99%

“…The metapelites, though rare, are important because they retain evidence of partial melting due to phengite breakdown (Lang and Gilotti, 2007) along a critical part of the exhumation path while the terrane was still at high pressure. Gilotti and McClelland (2007) suggested that partial melting began at approximately 347 Ma, based on U-Pb ages from a garnet-bearing granitic pegmatite in the neck of a boudinaged eclogite. Later, crosscutting leucosomes, with and without hornblende, give younger U-Pb zircon ages that range from about 340 Ma down to 320 Ma (errors on individual ages range from 2 to 5 Ma; Gilotti and McClelland, 2007;Gilotti et al, 2014;McClelland et al, 2009).…”

Section: Geologic Settingmentioning

confidence: 99%

“…1), relatively hot (≈ 950°C at 3.6 GPa) UHP conditions are documented by mineral assemblages, microstructures and thermobarometry on kyanite eclogites (Gilotti and Ravna, 2002), and by coesite inclusions in zircon (Gilotti et al, 2014;McClelland et al, 2006). However, the exhumation path from UHP conditions has only been estimated (Gilotti and McClelland, 2007). Evidence of partial melting is preserved in rare pelitic paragneisses that contain garnet megacrysts with complex compositional zoning and polyphase inclusions, and abundant leucosomes in the matrix (Lang and Gilotti, 2007).…”

Section: Introductionmentioning

confidence: 99%

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Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

Lang

Gilotti

2015

Lithos

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Pseudosection modeling constrains the pressure-temperature (P-T) exhumation path of partially melted ultrahigh-pressure (UHP) metapelites exposed in the North-East Greenland UHP terrane. A robust peak P and T estimate of 3.6 GPa and 970°C based on mineral assemblages in nearby kyanite eclogites is the starting point for the P-T path. Although the peak assemblage for the metapelite is not preserved, the calculated modeled peak assemblage contained substantial clinopyroxene, garnet, phengite, K-feldspar and coesite with minor kyanite and rutile. Combining the pseudosection and observed textures, the decompression path crosses the coesite-quartz transition before reaching the dry phengite dehydration melting reaction where phengite is abruptly consumed. In the range of 2.5 to 2.2 GPa, clinopyroxene is completely consumed and garnet grows to its maximum volume and grossular content, matching the high grossular rims of relict megacrysts. Plagioclase joins the assemblage and the pseudosection predicts up to 12-13 vol.% melt in the supersolidus assemblage, which contained garnet, liquid, K-feldspar, plagioclase, kyanite, quartz and rutile. At this stage, the steep decompression path flattened out and became nearly isobaric. The melt crystallization assemblage that formed when the path crossed the solidus with decreasing temperature contains phengite, garnet, biotite, 2 feldspars, kyanite, quartz and rutile. Therefore, the path must have intersected the solidus at approximately 1.2 GPa, 825°C. The pseudosection predicts that garnet is consumed on the cooling path, but little evidence of late garnet consumption or other retrograde effects is observed. This may be due to partial melt loss from the rock. Isochemical PT-n and PT-X sections calculated along the P-T path display changes in mineral assemblage and composition that are consistent with preserved assemblages.

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Section: Geologic Settingmentioning

confidence: 99%

Section: Geologic Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

Lang

Gilotti

2015

Lithos

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“…Ultrahigh-pressure durations lie in the range of 2-5 Myr for the exhumated complexes of northern Kazakhstan, the Western + Central Alps, the western Himalayas, and Eastern Papua, New Guinea (Sobolev and Shatsky, 1990;Gebauer et al, 1997;Hermann et al, 2001;Rubatto and Hermann, 2001;Hacker et al, 2003;Massonne and O'Brien, 2003;Treloar et al, 2003;Baldwin et al, 2004Baldwin et al, , 2008Leech et al, 2005;Massonne et al, 2007). In contrast, the largest UHP terranes, including those of east-central China, western China, East Greenland and coastal Norway appear to have been sequestered at great depth for $15-20 Myr (Hacker et al, , 2006Wu et al, 2006;Zhang et al, 2008a;Mattinson et al, 2006Mattinson et al, , 2007McClelland et al, 2006;Gilotti and McClelland, 2007;Yin et al, 2007;Kylander-Clark et al, 2008). One example is described below for Sulu UHP rocks.…”

Section: Duration Of Dabie-sulu Uhp Metamorphismmentioning

confidence: 99%

Ultrahigh-pressure minerals and metamorphic terranes – The view from China

Liou

Ernst

Zhang

et al. 2009

Journal of Asian Earth Sciences

315

161

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“…1) where diamond bearing UHP eclogites are exhumed within pervasively molten gneiss (Hacker et al, 2010;Kylander-Clark and Hacker, 2014). Zircon ages from leucosomes overlap with age interval for UHP peak metamorphism (Gordon et al, 2013). Polycrystalline inclusions in eclogitic rims of garnets (Ganzhorn et al, 2014) evidence presence of silicarich fluid at peak conditions and composition of early leucosomes are compatible with partial melting at UHP conditions (Labrousse et al, 2011).…”

Section: Geological Evidence Of Relations Between Uhp Metamorphics Exmentioning

confidence: 99%

H 2 O-fluid-saturated melting of subducted continental crust facilitates exhumation of ultrahigh-pressure rocks in continental subduction zones

Labrousse

Duretz

Gerya

2015

Earth and Planetary Science Letters

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We present two-dimensional numerical models of plate subduction and collision inspired by the Scandinavian Caledonian orogeny to investigate the possible impact of continental crust partial melting on the exhumation of ultra-high pressure metamorphic rocks. Three possible reactions were tested: low temperature solidus representing H 2 O-fluid-saturated partial melting, and two end-member reaction curves for dehydration melting. Thermo-mechanical effects of partial melting were implemented as (1) a viscosity decrease as a determined rheologically critical melt percentage was reached (here 0.1), (2) a change in effective heat capacity and adiabatic heating/cooling accounting for a latent heat term in the heat equation. Among the 3 tested reactions, only H 2 O-fluid-saturated partial melting drastically modifies the collision dynamics from the non-melting reference model holding all other parameters constant. A substantially low general viscosity truncation (here 10 17 Pa s) is needed to properly resolve the effect of partial melting on deep collision processes. Low temperature melting indeed induces the development of a low viscosity buoyant plume prior to slab detachment, where migmatites exhume from UHP conditions at rates and with pressure-temperature paths similar to the natural values acknowledged for the Norwegian Caledonides. High temperature melting has no drastic influence on early collision dynamics. While positive buoyancy remains the first order driver for the exhumation of buried continental rocks, exhumation initiates in these cases with eduction subsequent to slab detachment. Melting and formation of a migmatite plume can later occur along decompression path while continental crust undergoes thermal reequilibration at temperatures above 900 • C. Some of the partially molten material can also relaminate in the overriding plate rather than exhume within the collision zone. Even if minor in terms of amount of magma produced, H 2 O-fluid-saturated partial melting at UHP conditions could therefore have a dramatic rheological effect and actually limits continental rocks subduction and facilitates their exhumation.

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Characteristics of, and a Tectonic Model for, Ultrahigh-Pressure Metamorphism in the Overriding Plate of the Caledonian Orogen

Cited by 57 publications

References 90 publications

Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

Ultrahigh-pressure minerals and metamorphic terranes – The view from China

H 2 O-fluid-saturated melting of subducted continental crust facilitates exhumation of ultrahigh-pressure rocks in continental subduction zones

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