scholarly journals Extrusion of subducted crust explains the emplacement of far-travelled ophiolites

2021 ◽  
Author(s):  
Kristóf Porkoláb ◽  
Thibault Duretz ◽  
Philippe Yamato ◽  
Antoine Auzemery ◽  
Ernst Willingshofer
Keyword(s):  
High Pressure ◽  
Continental Crust ◽  
Plate Tectonics ◽  
Oceanic Lithosphere ◽  
Causal Link ◽  
Combine Data ◽  
Continental Subduction ◽  
Ophiolite Emplacement ◽  
Oceanic Plates ◽  
Tectonic Windows

<p>Continental subduction below oceanic plates and associated emplacement of ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit a far-travelled ophiolite sheet that is separated from its oceanic root by tectonic windows exposing continental crust, which experienced subduction-related high pressure-low temperature (HP-LT) metamorphism during obduction. However, the link between continental subduction-exhumation dynamics and far-travelled ophiolite emplacement remains poorly understood. We combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the extrusion of subducted continental crust and the emplacement of far-travelled ophiolite sheets. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. The broken-off piece of oceanic lithosphere is then transported on top of the continent along a flat thrust segment and becomes a far-travelled ophiolite sheet separated from its root by the extruded continental crust. Our results indicate that the extrusion of the subducted continental crust and the emplacement of far-travelled ophiolite sheets are inseparable processes.</p>

scholarly journals Extrusion of subducted crust explains the emplacement of far-travelled ophiolites

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kristóf Porkoláb ◽  
Thibault Duretz ◽  
Philippe Yamato ◽  
Antoine Auzemery ◽  
Ernst Willingshofer
Keyword(s):  
High Pressure ◽  
Continental Crust ◽  
Plate Tectonics ◽  
Oceanic Lithosphere ◽  
Causal Link ◽  
Combine Data ◽  
Continental Subduction ◽  
Ophiolite Emplacement ◽  
Oceanic Plates ◽  
Tectonic Windows

AbstractContinental subduction below oceanic plates and associated emplacement of ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit a far-travelled ophiolite sheet that is separated from its oceanic root by tectonic windows exposing continental crust, which experienced subduction-related high pressure-low temperature metamorphism during obduction. However, the link between continental subduction-exhumation dynamics and far-travelled ophiolite emplacement remains poorly understood. Here we combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the extrusion of subducted continental crust and the emplacement of far-travelled ophiolites. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. The broken-off piece of oceanic lithosphere is then transported on top of the continent along a flat thrust segment and becomes a far-travelled ophiolite sheet separated from its root by the extruded continental crust. Our results indicate that the extrusion of the subducted continental crust and the emplacement of far-travelled ophiolite sheets are inseparable processes.

scholarly journals Extrusion of subducted crust explains the emplacement of far-travelled ophiolites

2020 ◽  
Author(s):  
Kristóf Porkoláb ◽  
Thibault Duretz ◽  
Philippe Yamato ◽  
Antoine Auzemery ◽  
Ernst Willingshofer
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Causal Link ◽  
Upper Crust ◽  
Combine Data ◽  
Continental Subduction ◽  
Ophiolite Emplacement ◽  
Oceanic Plates ◽  
Shed Light ◽  
Oceanic Domain

Abstract Continental subduction below oceanic plates and associated emplacement of far-travelled ophiolite sheets remain enigmatic chapters in global plate tectonics. Numerous ophiolite belts on Earth exhibit continental rocks that experienced subduction-related high pressure-low temperature (HP-LT) metamorphism and subsequent exhumation coeval with the emplacement of ophiolites. However, the link between continental subduction dynamics and ophiolite emplacement is poorly understood. Here we combine data collected from ophiolite belts worldwide with thermo-mechanical simulations of continental subduction dynamics to show the causal link between the exhumation of subducted continental crust and ophiolite emplacement. Our results reveal that buoyancy-driven extrusion of subducted crust triggers necking and breaking of the overriding oceanic upper plate. This process is fundamental for the formation of a far-travelled ophiolite sheet that is separated from the oceanic domain by the exhumed, HP-LT continental upper crust. Our results indicate that the exhumation of the subducted continental crust and far-travelled ophiolite sheet emplacement are inseparable processes and thus shed light on one of the most mysterious aspect of plate tectonics.

scholarly journals No evidence for high-pressure melting of Earth’s crust in the Archean

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Robert H. Smithies ◽  
Yongjun Lu ◽  
Tim E. Johnson ◽  
Christopher L. Kirkland ◽  
Kevin F. Cassidy ◽  
...  
Keyword(s):  
High Pressure ◽  
Continental Crust ◽  
Small Proportion ◽  
Lithospheric Mantle ◽  
Plate Tectonics ◽  
Crustal Evolution ◽  
Average Thickness ◽  
Dominant Group ◽  
Chemical Signatures ◽  
Pressure Melting

AbstractMuch of the present-day volume of Earth’s continental crust had formed by the end of the Archean Eon, 2.5 billion years ago, through the conversion of basaltic (mafic) crust into sodic granite of tonalite, trondhjemite and granodiorite (TTG) composition. Distinctive chemical signatures in a small proportion of these rocks, the so-called high-pressure TTG, are interpreted to indicate partial melting of hydrated crust at pressures above 1.5 GPa (>50 km depth), pressures typically not reached in post-Archean continental crust. These interpretations significantly influence views on early crustal evolution and the onset of plate tectonics. Here we show that high-pressure TTG did not form through melting of crust, but through fractionation of melts derived from metasomatically enriched lithospheric mantle. Although the remaining, and dominant, group of Archean TTG did form through melting of hydrated mafic crust, there is no evidence that this occurred at depths significantly greater than the ~40 km average thickness of modern continental crust.

scholarly journals Conductive Channels in the Deep Oceanic Lithosphere Could Consist of Garnet Pyroxenites at the Fossilized Lithosphere–Asthenosphere Boundary

Minerals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1107
Author(s):  
Thomas P. Ferrand
Keyword(s):  
Plate Tectonics ◽  
Early Stage ◽  
Experimental Petrology ◽  
Oceanic Lithosphere ◽  
High Conductivity ◽  
Stability Field ◽  
Cocos Plate ◽  
Lithospheric Plates ◽  
Oceanic Plates ◽  
Garnet Stability Field

Magnetotelluric (MT) surveys have identified anisotropic conductive anomalies in the mantle of the Cocos and Nazca oceanic plates, respectively, offshore Nicaragua and in the eastern neighborhood of the East Pacific Rise (EPR). Both the origin and nature of these anomalies are controversial as well as their role in plate tectonics. The high electrical conductivity has been hypothesized to originate from partial melting and melt pooling at the lithosphere–asthenosphere boundary (LAB). The anisotropic nature of the anomaly likely highlights high-conductivity channels in the spreading direction, which could be further interpreted as the persistence of a stable liquid silicate throughout the whole oceanic cycle, on which the lithospheric plates would slide by shearing. However, considering minor hydration, some mantle minerals can be as conductive as silicate melts. Here I show that the observed electrical anomaly offshore Nicaragua does not correlate with the LAB but instead with the top of the garnet stability field and that garnet networks suffice to explain the reported conductivity values. I further propose that this anomaly actually corresponds to the fossilized trace of the early-stage LAB that formed near the EPR about 23 million years ago. Melt-bearing channels and/or pyroxenite underplating at the bottom of the young Cocos plate would transform into garnet-rich pyroxenites with decreasing temperature, forming solid-state high-conductivity channels between 40 and 65 km depth (1.25–1.9 GPa, 1000–1100 °C), consistently with experimental petrology.

scholarly journals Up the down escalator: the exhumation of (ultra)-high pressure terranes during on-going subduction

2012 ◽  
Vol 4 (1) ◽  
pp. 745-781 ◽  
Author(s):  
C. J. Warren
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Continental Crust ◽  
Subduction Zones ◽  
Crustal Material ◽  
Time And Space ◽  
Ultra High Pressure ◽  
Tectonic Environment ◽  
Tectonic Style ◽  
Weak Material

Abstract. The exhumation of high and ultra-high pressure rocks is ubiquitous in Phanerozoic orogens created during continental collisions, and is common in many ocean-ocean and ocean-continent subduction zone environments. Three different tectonic environments have previously been reported, which exhume deeply buried material by different mechanisms and at different rates. However it is becoming increasingly clear that no single mechanism dominates in any particular tectonic environment, and the mechanism may change in time and space within the same subduction zone. In order for buoyant continental crust to subduct, it must remain attached to a stronger and denser substrate, but in order to exhume, it must detach (and therefore at least locally weaken) and be initially buoyant. Denser oceanic crust subducts more readily than more buoyant continental crust but exhumation must be assisted by entrainment within more buoyant and weak material such as serpentinite or driven by the exhumation of structurally lower continental crustal material. Weakening mechanisms responsible for the detachment of crust at depth include strain, hydration, melting, grain size reduction and the development of foliation. These may act locally or may act on the bulk of the subducted material. Metamorphic reactions, metastability and the composition of the subducted crust all affect buoyancy and overall strength. Subduction zones change in style both in time and space, and exhumation mechanisms change to reflect the tectonic style and overall force regime within the subduction zone. Exhumation events may be transient and occur only once in a particular subduction zone or orogen, or may be more continuous or occur multiple times.

Relative roles of source composition, fractional crystallization and crustal contamination in the petrogenesis of Andean volcanic rocks

1984 ◽  
Vol 310 (1514) ◽  
pp. 675-692 ◽  
Keyword(s):  
Subduction Zone ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Alkaline Basalt ◽  
Complex Process ◽  
Heterogeneous Mantle

There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt—andesite-dacite-rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt-trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of ‘within-plate’ character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust.

scholarly journals Intraplate volcanism triggered by bursts in slab flux

2020 ◽  
Vol 6 (51) ◽  
pp. eabd0953
Author(s):  
Ben R. Mather ◽  
R. Dietmar Müller ◽  
Maria Seton ◽  
Saskia Ruttor ◽  
Oliver Nebel ◽  
...  
Keyword(s):  
Transition Zone ◽  
Plate Tectonics ◽  
Isotope Geochemistry ◽  
Plate Boundary ◽  
Oceanic Lithosphere ◽  
Mantle Transition Zone ◽  
Age Progression ◽  
Intraplate Volcanism ◽  
Enriched Mantle ◽  
Eastern Australia

Long-lived, widespread intraplate volcanism without age progression is one of the most controversial features of plate tectonics. Previously proposed edge-driven convection, asthenospheric shear, and lithospheric detachment fail to explain the ~5000-km-wide intraplate volcanic province from eastern Australia to Zealandia. We model the subducted slab volume over 100 million years and find that slab flux drives volcanic eruption frequency, indicating stimulation of an enriched mantle transition zone reservoir. Volcanic isotope geochemistry allows us to distinguish a high-μ (HIMU) reservoir [>1 billion years (Ga) old] in the slab-poor south, from a northern EM1/EM2 reservoir, reflecting a more recent voluminous influx of oceanic lithosphere into the mantle transition zone. We provide a unified theory linking plate boundary and slab volume reconstructions to upper mantle reservoirs and intraplate volcano geochemistry.

scholarly journals Constraining crustal silica on ancient Earth

2020 ◽  
Vol 117 (35) ◽  
pp. 21101-21107 ◽  
Author(s):  
C. Brenhin Keller ◽  
T. Mark Harrison
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Incompatible Element ◽  
Silica Content ◽  
Efficient Mechanism ◽  
Element Abundances ◽  
Terrigenous Sediments ◽  
Earth History ◽  
Crustal Composition ◽  
Earth’S Mantle

Accurately quantifying the composition of continental crust on Hadean and Archean Earth is critical to our understanding of the physiography, tectonics, and climate of our planet at the dawn of life. One longstanding paradigm involves the growth of a relatively mafic planetary crust over the first 1 to 2 billion years of Earth history, implying a lack of modern plate tectonics and a paucity of subaerial crust, and consequently lacking an efficient mechanism to regulate climate. Others have proposed a more uniformitarian view in which Archean and Hadean continents were only slightly more mafic than at present. Apart from complications in assessing early crustal composition introduced by crustal preservation and sampling biases, effects such as the secular cooling of Earth’s mantle and the biologically driven oxidation of Earth’s atmosphere have not been fully investigated. We find that the former complicates efforts to infer crustal silica from compatible or incompatible element abundances, while the latter undermines estimates of crustal silica content inferred from terrigenous sediments. Accounting for these complications, we find that the data are most parsimoniously explained by a model with nearly constant crustal silica since at least the early Archean.

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