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

2015 ◽  
Vol 56 (7) ◽  
pp. 1016-1034 ◽  
Author(s):  
V.S. Shatsky ◽  
S.Yu. Skuzovatov ◽  
A.L. Ragozin ◽  
N.V. Sobolev
Keyword(s):  
Subduction Zone ◽  
Metamorphic Complex ◽  
Kokchetav Massif ◽  
Continental Subduction ◽  
Mobility Of Elements

Timing of subduction zone metamorphism during the formation and emplacement of Troodos and Baer–Bassit ophiolites: insights from 40Ar–39Ar geochronology

2007 ◽  
Vol 144 (5) ◽  
pp. 797-810 ◽  
Author(s):  
GAVIN HEUNG-NGAI CHAN ◽  
JOHN MALPAS ◽  
COSTAS XENOPHONTOS ◽  
CHING-HUA LO
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Accretionary Prism ◽  
Passive Margin ◽  
Metamorphic Rocks ◽  
Metamorphic Complex ◽  
Troodos Ophiolite ◽  
Crustal Thinning ◽  
Step Heating ◽  
Short Time

The Troodos ophiolite in Cyprus and Baer–Bassit ophiolite in Syria together form part of the Tethyan ophiolite belt. They were generated in a supra-subduction zone setting in Late Cretaceous times. As with many of the ophiolite occurrences in this belt, the sequences are closely associated with tectonic ‘coloured mélange’ zones, which contain, among a variety of lithologies, metre- to kilometre-size blocks of metamorphic rocks. Precise 40Ar–39Ar laser step-heating experiments performed on four amphibolites from SW Cyprus and six from NW Syria, yield plateau ages ranging from 75.7±0.3 Ma to 88.9±0.8 Ma in Cyprus and 71.7±0.5 to 88.4±0.4 Ma in Syria. The older limits of these time spans are coeval with the age of the formation of the associated ophiolites. Unlike other metamorphic sole rocks which seem to form in relatively short time spans, these metamorphic rocks found in Cyprus and Syria are interpreted to have formed in Late Cretaceous times by accretion below the overriding Troodos and Baer–Bassit crust for a period of 15–18 Ma. The metamorphic complexes were exhumed by extension and crustal thinning associated with subduction roll-back and the rotation of the overriding plate until the cessation of subduction in Maastrichtian times. In Cyprus, the exhumed metamorphic complex was incorporated into an accretionary prism constructed primarily of the collapsed Mamonia passive margin sequence intercalated with rocks of the Troodos ophiolite during plate collision in the Maastrichtian. Concomitantly, in Syria, the Baer–Bassit ophiolite and subcreted metamorphic complex were emplaced onto the Arabian passive margin and fragmented into blocks and knockers, forming the Baer–Bassit mélange.

Petrotectonic implications of metabasites of the Eastern Andean Metamorphic Complex at Lago O´Higgins-San Martin, southern Patagonia

2021 ◽  
Author(s):  
Diego Rojo ◽  
Mauricio Calderón ◽  
Matias Ghiglione ◽  
Rodrigo Javier Suárez ◽  
Paulo Quezada ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Passive Margin ◽  
Low Grade ◽  
Accretionary Wedge ◽  
Metamorphic Complex ◽  
Marginal Basin ◽  
Southern Patagonia ◽  
San Martín

<p>The Eastern Andean Metamorphic Complex (EAMC) in southwestern Patagonia (4°-52°S) is a 450 km long belt mainly composed by low-grade metasedimentary rocks of Upper Devonian-lower Carboniferous, and Permian-lower Triassic ages. Previous works have suggested a passive margin environment for the deposition of the protolith.  The EAMC comprise scarce interleaved tectonic slices of marbles, metabasites, and exceptional serpentinite bodies. At Lago O´Higgins-San Martin (48°30’S-49°00’S) the metasedimentary sucessions are tectonically juxtaposed with lenses of pillowed metabasalts and greenschists having OIB, N-MORB, BABB and IAT geochemical affinities. The Nd-isotopic composition of metabasalts is characterized by εNd<sub>(t=350 Ma)</sub> of +6 and +7. The metabasalts show no signal of crustal contamination, instead, the mantle source was probably modified by subduction components. New and already published provenance data based on mineralogy, geochemistry and zircon geochronology indicate that the quartz-rich protolith of metasandstones were deposited during late Devonian-early Carboniferous times (youngest single zircon ages around of latest Devonian-earliest Carboniferous times) sourced from igneous and/or sedimentary rocks located in the interior of Gondwana, as the Deseado Massif, for instance. Noticeable, the detrital age patterns of all samples reveal a prominent population of late Neoproterozoic zircons, probably directly derived from igneous and/or metaigneous rocks of the Brasiliano/Pan-African orogen or from reworked material from variably metamorphosed sedimentary units that crops out at the same latitudes in the extra-Andean region of Patagonia. We propose that the protolith of metabasites formed part of the upper part of an oceanic-like lithosphere generated in a marginal basin above a supra-subduction zone, where plume-related oceanic island volcanoes were generated. The closure of the marginal basin, probably in mid-Carboniferous times, or soon after. The oceanic lithosphere was likely underthrusted within an east-to-northeast-dipping subduction zone, where ophiolitic rocks and metasedimentary sequences were tectonically interleaved at the base of an accretionary wedge.</p>

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