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Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

ABSTRACT: Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins.

SUBMITTER: Zhao ZF

PROVIDER: S-EPMC3849635 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

Zhao Zi-Fu ZF Dai Li-Qun LQ Zheng Yong-Fei YF

Scientific reports 20131204

Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance ...[more]

PMID: 24301173

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Project description:Relicts of subducted oceanic lithosphere provide key information for the tectonic reconstructions of convergent margins. In the Central Alps, such relicts occur as isolated mafic-ultramafic lenses within the migmatites of the southern Adula nappe and Cima-Lunga unit. Analysis of the major-, minor-, and accessory minerals of these ophiolitic relicts, combined with zircon and rutile U-Pb ages and zircon oxygen isotopes, allows the reconstruction of different stages of their complex evolution. The mafic-ultramafic suite in Valle di Moleno consists of chlorite-harzburgites associated with metarodingites and retrogressed eclogites. Relic omphacite and kyanite in retrogressed eclogites provide evidence for subduction-related metamorphism. Increasing XPrp in the garnet mantle towards the rim documents heating during high-pressure metamorphism up to 800-850 °C. Polyphase inclusions and chemical zoning in garnet suggest fluid-assisted melting during high-pressure metamorphism dated at 31.0 ± 0.9 Ma. In Val Cama, chlorite-harzburgites, metarodingites and calcsilicate-metasediments occur. Detrital zircon ages in the metasediment suggest a Mesozoic deposition. The metarodingite-metaperidotite-metasediment association and the low δ18O signatures of zircon (δ18O 3.0-3.7‰), inherited from seafloor metasomatism of the protoliths, show that the rocks are derived from former altered oceanic crust. Amphibolite facies metamorphism related to the Central Alps Barrovian evolution in Val Cama occurred at 28.8 ± 1.5 Ma. The combined data from Moleno and Cama indicate a rapid transition (~ 2 Ma) from subduction to collisional metamorphism with corresponding exhumation rates of 3-6 cm/year. Fast exhumation tectonics may have been favored by slab break-off or slab extraction. U-Pb dating of rutile from both localities yields ages of ~ 20 Ma, suggesting that these rocks remained at amphibolite-facies conditions for about 10 Ma and underwent a second fast exhumation of 3 cm/year associated with vertical movements along the Insubric line.Supplementary informationThe online version contains supplementary material available at 10.1186/s00015-024-00462-7.

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Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

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Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

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