Mechanisms of continental subduction and exhumation of HP and UHP rocks

Burov, Evgenii; François, Thomas; Yamato, Philippe; Wolf, Sylvie

doi:10.1016/j.gr.2012.09.010

Cited by 71 publications

(32 citation statements)

References 111 publications

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“…In addition, synconvergent models predict that rapid exhumation and stacking of (U)HP units at the base of the crust is followed by slower trans‐crustal exhumation. Such a prediction is not specific of the model analyzed in Figure , but it is also common to other synconvergent exhumation models incorporating a free behavior of the slab [e.g., Yamato et al ., , 2008; Burov et al ., ]. However, HP rocks of the Western Alps have been rapidly exhumed directly to the Earth's surface in the Eocene, where they were covered by sediments by 32 Ma (black star in Figure e).…”

Section: Comparison With Synconvergent Exhumation Modelsmentioning

confidence: 99%

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

Malusà

Faccenna

Baldwin

et al. 2015

Geochem Geophys Geosyst

118

145

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Since the first discovery of ultrahigh pressure (UHP) rocks 30 years ago in the Western Alps, the mechanisms for exhumation of (U)HP terranes worldwide are still debated. In the western Mediterranean, the presently accepted model of synconvergent exhumation (e.g., the channel-flow model) is in conflict with parts of the geologic record. We synthesize regional geologic data and present alternative exhumation mechanisms that consider the role of divergence within subduction zones. These mechanisms, i.e., (i) the motion of the upper plate away from the trench and (ii) the rollback of the lower plate, are discussed in detail with particular reference to the Cenozoic Adria-Europe plate boundary, and along three different transects (Western Alps, Calabria-Sardinia, and Corsica-Northern Apennines). In the Western Alps, (U)HP rocks were exhumed from the greatest depth at the rear of the accretionary wedge during motion of the upper plate away from the trench. Exhumation was extremely fast, and associated with very low geothermal gradients. In Calabria, HP rocks were exhumed from shallower depths and at lower rates during rollback of the Adriatic plate, with repeated exhumation pulses progressively younging toward the foreland. Both mechanisms were active to create boundary divergence along the Corsica-Northern Apennines transect, where European southeastward subduction was progressively replaced along strike by Adriatic northwestward subduction. The tectonic scenario depicted for the Western Alps trench during Eocene exhumation of (U)HP rocks correlates well with present-day eastern Papua New Guinea, which is presented as a modern analog of the Paleogene Adria-Europe plate boundary.

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Section: Comparison With Synconvergent Exhumation Modelsmentioning

confidence: 99%

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

Malusà

Faccenna

Baldwin

et al. 2015

Geochem Geophys Geosyst

118

145

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“…Since the subduction of continental crust was preceded by the subduction of oceanic crust (Burov et al, 2014), one should expect that the mantle wedge above the zone of continental subduction was hydrated during oceanic subduction. Even in the absence of hydrous minerals, such as amphiboles and serpentine, water can be present in nominally anhydrous minerals (Zheng and Hermann, 2014).…”

Section: Evidence For Rock Melting Above the Second Critical Pointmentioning

confidence: 99%

Mobility of elements in a continental subduction zone: evidence from the UHP metamorphic complex of the Kokchetav massif

Shatsky

Skuzovatov

Ragozin

et al. 2015

Russian Geology and Geophysics

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We studied clastics of high-alumina garnet-kyanite-mica schists and garnet-kyanite-quartz granofelses, including diamond-bearing ones, found in the eluvial sediments near Lake Barchi. In contents of major elements the studied rocks correspond to argillaceous shales. The garnet-kyanite-quartz granofelses are poorer in K (0.49-1.35 wt.% K 2 O) than the garnet-kyanite-mica schists (4.9-2.2 wt.% K 2 O) but have the same contents of other major components. The REE patterns of most of the garnet-kyanite-phengite schists are similar to those of the Post-Archean Australian Shale (PAAS) (x _ La/Yb = 13). All garnet-kyanite-quartz rocks are much stronger depleted in LREE (x _ La/Yb = 1.4) and other incompatible elements. Our studies show that allanite and monazite are the main concentrators of LREE and Th in the garnet-kyanite-phengite rocks of the Barchi site. Monazite, occurring as inclusions in garnet, contains not only LREE but also Th, U, and Pb. Rutile of the nondepleted rocks is enriched in Fe and Nb impurities only. The garnet-kyanite-quartz granofelses bear rutile, apatite, and xenotime as accessory phases. Rutile of the depleted rocks shows wide variations in contents of Nb, Ta, and V impurities. In places, the contents of Nb and Ta reach 10.5 and 2.3 wt.%, respectively. The rutile decomposes into rutile with Nb (1.4 wt.%) and Fe (0.87 wt.%) impurities and titanium oxide rich in Fe (6.61 wt.%), Nb (up to 20.8 wt.%), and Ta (up to 2.81%) impurities. Based on the measured contents of incompatible elements in differently depleted high-alumina rocks, the following series of element mobility during UHP metamorphism has been established: Th > Ce > La > Pr > Nd > K > Ba > Rb > Cs > Sm > Eu. The contents of U, P, and Zr in the depleted rocks are similar to those in the nondepleted rocks. The studies have shown that metapelites subducted to the depths with diamond stability conditions can be depleted to different degrees. This might be either due to their exhumation from different depths of the subduction zone or to the presence of an external source of water controlling the temperature of dissolution of phengite and the formation of supercritical fluid/melt.

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“…Exhumation of HP crustal rocks along continental collision zones that followed subduction (e.g. Gerya et al, 2008;Yamato et al, 2008;Burov et al, 2012) was explained with a decreasing strength and density of deep seated crustal 'melanges' forced by rigid and dense surrounding material. Slab retreat, break-off (Ueda et al, 2012), or a change in the far-field convergence regime reduce the confinement that retains buoyant melts at depth and thus facilitates their exhumation.…”

Section: Introductionmentioning

confidence: 99%

Crustal exhumation during ongoing compression in the Variscan Maures-Tanneron Massif, France-Geological and thermo-mechanical aspects

et al. 2018

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The Maures-Tanneron Massif (MTM), together with Corsica and Sardinia, represent the Southeastern branch of the huge European Variscan belt. A continuous evolution from continental collision to exhumation is described from ca. 350 Ma to ca. 320 Ma, based on an extended compilation of available geological and geochronogical data. This geological compilation is complemented with thermo-mechanical modelling that tests the conditions under which deep-seated HP units can melt and exhume massively during continued convergence. We simulate in two-dimensions the development of gravitational instabilities in a partially melting crust, depending on rheological layering and heat sources, and accounting for temperature dependent elasto-visco-plastic rheologies. In order to reproduce PT exhumation patterns in the MTM, over the appropriate time-scale (>20 My) and spatial extent (>100 km), a best fit was obtained with a convergence rate of 0.5 cm/yr and moderate diffusive surface processes. The contribution of radiogenic heating in the pre-stacked felsic crustal units is crucial. A lateral alternation with mafic units is also required in order to prevent lateral spreading of the orogen. A low viscosity partially molten crust (10² Pa.s, thus rather felsic) accompanies crustal exhumation in a decoupled mode from the deeper mantle. A shallow asthenosphere below the orogen (LAB at ~70 km depth, eg. shallow slab break-off) produces too warm and sudden exhumation as opposed to a competent mantle lithosphere (120 km depth LAB) that restrains it. The MTM witnesses the typical competition between far-field plate convergence and internal body forces, and our study pleads for a progressive evolution of transpression towards perpendicular extension from ca. 320 Ma.

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Mechanisms of continental subduction and exhumation of HP and UHP rocks

Cited by 71 publications

References 111 publications

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

Contrasting styles of (U)HP rock exhumation along the Cenozoic Adria‐Europe plate boundary (Western Alps, Calabria, Corsica)

Mobility of elements in a continental subduction zone: evidence from the UHP metamorphic complex of the Kokchetav massif

Crustal exhumation during ongoing compression in the Variscan Maures-Tanneron Massif, France-Geological and thermo-mechanical aspects

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