scholarly journals Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)

2011 ◽  
Vol 3 (1) ◽  
pp. 477-526
Author(s):  
M. Nasrabady ◽  
F. Rossetti ◽  
T. Theye ◽  
G. Vignaroli
Keyword(s):  
Subduction Zone ◽  
Early Cretaceous ◽  
Oceanic Lithosphere ◽  
Geochemical Data ◽  
Data Set ◽  
Metamorphic History ◽  
History Of ◽  
Back Arc ◽  
Temperature Path ◽  
Ne Iran

Abstract. The Iranian ophiolites are part of the vast orogenic suture zones that mark the Alpine-Himalayan convergence zone. Few petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing and regimes of subduction zone metamorphism and orogenic construction in the region. This paper describes texture, geochemistry and the pressure-temperature path of the Early Cretaceous granulites that occur within the Tertiary Sabzevar suture zone of NE Iran. The geochemical data set document that the granulites are remnants of a MORB-type oceanic crust and thus of a (Early Cretaceous ?) back-arc basin formed in the upper plate of the Neotethyan subduction and thus interpreted as portions of a dismembered dynamothermal sole formed during oceanic subduction. The metamorphic history of the granulites suggests an anticlockwise pressure-temperature loop, compatible with burial in a hot subduction zone followed by cooling during exhumation. This is interpreted as the evidence of a nascent subduction zone formed at the expenses of hot and hence young oceanic lithosphere. These data point to diachronous and independent tectonic evolutions of the different ophiolitic domains of central Iran, for which a growing heterogeneity in the timing of metamorphic equilibration and of pressure-temperature paths can be expected with further investigations.

scholarly journals Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)

Solid Earth ◽  
2011 ◽  
Vol 2 (2) ◽  
pp. 219-243 ◽  
Author(s):  
M. Nasrabady ◽  
F. Rossetti ◽  
T. Theye ◽  
G. Vignaroli
Keyword(s):  
Subduction Zone ◽  
Early Cretaceous ◽  
Mature Stage ◽  
Convergence Zone ◽  
Geochronological Data ◽  
Metamorphic History ◽  
History Of ◽  
Back Arc ◽  
Temperature Path ◽  
Ne Iran

Abstract. The Iranian ophiolites are part of the vast orogenic suture zones that mark the Alpine-Himalayan convergence zone. Few petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing and regimes of subduction zone metamorphism and orogenic construction in the region. This paper describes texture, geochemistry, and the pressure-temperature path of the Early Cretaceous mafic granulites that occur within the Tertiary Sabzevar ophiolitic suture zone of NE Iran. Whole rock geochemistry indicates that the Sabzevar granulites are likely derived from a MORB-type precursor. They are thus considered as remnants of a dismembered dynamo-thermal sole formed during subduction of a back-arc basin (proto-Sabzevar Ocean) formed in the upper-plate of the Neotethyan slab. The metamorphic history of the granulites suggests an anticlockwise pressure-temperature loop compatible with burial in a hot subduction zone, followed by cooling during exhumation. Transition from a nascent to a mature stage of oceanic subduction is the geodynamic scenario proposed to accomplish for the reconstructed thermobaric evolution. When framed with the regional scenario, results of this study point to diachronous and independent tectonic evolutions of the different ophiolitic domains of central Iran, for which a growing disparity in the timing of metamorphic equilibration and of pressure-temperature paths can be expected to emerge with further investigations.

The ophiolites of the Tibetan Geotraverses, Lhasa to Golmud (1985) and Lhasa to Kathmandu (1986)

1988 ◽  
Vol 327 (1594) ◽  
pp. 215-238 ◽  
Keyword(s):  
Subduction Zone ◽  
Oceanic Lithosphere ◽  
Island Arc ◽  
Passive Margin ◽  
Jinsha River ◽  
Geochemical Composition ◽  
The North ◽  
Kunlun Mountains ◽  
Slow Spreading ◽  
Back Arc

Ophiolite belts are found in Tibet along the Zangbo, Banggong and Jinsha River Sutures and in the Anyemaqen mountains, the eastern extension of the Kunlun mountains. Where studied, the Zangbo Suture ophiolites are characterized by: apparently thin crustal sequences (3-3.5 k m ); an abundance of sills and dykes throughout the crustal and uppermost mantle sequences; common intraoceanic melanges and unconformities; and an N-MORB petrological and geochemical composition. The ophiolites probably formed within the main neo-Tethyan ocean and the unusual features may be due to proximity to ridge-transform intersections, rather than to genesis at very slow -spreading ridges as the current consensus suggests. The Banggong Suture ophiolites have a supra-subduction zone petrological and geochemical composition — although at least one locality in the Ado Massif shows MORB characteristics. However, it is also apparent that the dykes and lavas show a regional chemical zonation, from boninites and primitive island arc tholeiites in the south of the ophiolite belt, through normal island arc tholeiites in the central belt to island arc tholeiites transitional to N-MORB in the north. The ophiolites could represent fragments of a fore-arc, island arc, back-arc complex developed above a Jurassic, northward-dipping subduction zone and emplaced in several stages during convergence of the Lhasa and Qiangtang terranes. The ophiolites of the Jinsha River Suture have a N-MORB composition where analysed, but more information is needed for a proper characterization. The Anyemaqen ophiolites, where studied, have a within-plate tholeiite composition and may have originated at a passive margin: it is not, however, certain whether true oceanic lithosphere, as opposed to strongly attenuated continental lithosphere, existed in this region.

scholarly journals Correlation of Elastic Moduli and Serpentine Content in Ultramafic Rocks

2019 ◽  
Author(s):  
Aida Farough ◽  
Alexander Karrasch
Keyword(s):  
Physical Properties ◽  
Lower Crust ◽  
Elastic Moduli ◽  
Oceanic Lithosphere ◽  
Ultramafic Rocks ◽  
Seismic Velocities ◽  
Rock Composition ◽  
Metamorphic History ◽  
History Of ◽  
Thin Crust

Understanding the physical properties of ultramafic rocks is important for evaluating awide variety of petrologic models of the oceanic lithosphere, particularly upper mantle and lower crust. Hydration of oceanic peridotites results in increasing serpentine content, which affects lithospheric physical properties and the global bio/geochemical cycles of various elements. In understanding tectonic, magmatic and metamorphic history of the oceanic crust, interpreting seismic velocities, rock composition and elastic moduli are of fundamental importance. In this study we show that as serpentine content increases, density decreases linearly with a slope of 7.85. We also correlate increase in serpentine content with a linear decline in shear, bulk and Young’s moduli with slopes of 0.48, 0.77, 0.45 respectively. Our results show that increase in serpentine content of lower crust and forearc mantle could decrease elasticity of lithospehere and result in break-offs. Therefore tectonic processes at peridotite rich slow spreading ridges may be strongly affected by serpentine content, particularly serpentinization may be responsible for discontinuities in thin crust, and formation of weak fault zones.

Sabzevar Ophiolite, NE Iran: Progress from embryonic oceanic lithosphere into magmatic arc constrained by new isotopic and geochemical data

Lithos ◽  
2014 ◽  
Vol 210-211 ◽  
pp. 224-241 ◽  
Author(s):  
Hadi Shafaii Moghadam ◽  
Fernando Corfu ◽  
Massimo Chiaradia ◽  
Robert J. Stern ◽  
Ghasem Ghorbani
Keyword(s):  
Oceanic Lithosphere ◽  
Geochemical Data ◽  
Magmatic Arc ◽  
Ne Iran

Early Cambrian back-arc volcanism in the western Taurides, Turkey: implications for rifting along the northern Gondwanan margin

2005 ◽  
Vol 142 (5) ◽  
pp. 617-631 ◽  
Author(s):  
S. GÜRSU ◽  
M. C. GÖNCÜOGLU
Keyword(s):  
Oceanic Lithosphere ◽  
Tholeiitic Basalt ◽  
Central Anatolia ◽  
Geochemical Data ◽  
Low Grade ◽  
Early Cambrian ◽  
Spinel Lherzolite ◽  
Mafic Rocks ◽  
Clastic Rocks ◽  
Back Arc

The Lower Cambrian (Tommotian) Gögebakan Formation in western Central Anatolia is made up of slightly metamorphosed continental to shallow marine clastic rocks with pillowed and massive spilitic lavas and dolerite dykes. Spilitic lavas, commonly amygdaloidal, are albite- and pyroxene-phyric with the metamorphic mineral paragenesis albite+calcite+sericite±epidote±tremolite±chlorite. Dolerite dykes mainly include plagioclase and pyroxene as primary minerals and tremolite±epidote±chlorite as low-grade secondary minerals. Geochemical data show that the spilitic lavas and dolerite dykes are sub-alkaline, of oceanic tholeiitic basalt character and display a tholeiitic fractional trend, characterized by an increase in FeO/MgO and Zr and TiO2 in variation diagrams. They are characterized by relatively high Zr/Y (2–4.5), relatively high Th/Yb (0.15–1.0) and La/Nb (0.5–2.5). Both show marked negative Nb and Ti anomalies relative to Th and La (Ce), implying a subduction-related chemistry. Chondrite-normalized REE patterns display slight enrichment of light REE (spilitic lavas (La/Yb)N = 0.79–1.56; dolerite dykes (La/Yb)N = 0.89–3.50) fairly comparable with MORB. The geochemical similarity of the spilitic lavas and dolerite dykes suggests a co-genetic origin. La/Nb ratios of both types are slightly higher than average MORB values and were possibly formed in the early stages of back-arc basin development. Petrogenetic modelling suggests the mafic rocks of the formation were formed by 9% batch melting of spinel lherzolite in shallower depths (c. 60 km). Taken together the data suggest that the Early Cambrian mafic rocks of the Taurus units were developed in a back-arc basin along the northern edge of Gondwana above the southward-subducting oceanic lithosphere and may represent initial rifting that resulted in separation of the peri-Gondwanan terranes.

scholarly journals Ancient Melt Depletion and Metasomatic History of the Subduction Zone Mantle: Osmium Isotope Evidence of Peridotites from the Yap Trench, Western Pacific

Minerals ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 717
Author(s):  
Ling Chen ◽  
Limei Tang ◽  
Xiaohu Li ◽  
Jie Zhang ◽  
Wei Wang ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Western Pacific ◽  
Arc Melting ◽  
Depleted Mantle ◽  
Mantle Peridotites ◽  
Os Isotopes ◽  
History Of ◽  
Isotope Evidence ◽  
Oceanic Asthenosphere ◽  
Back Arc

Highly depleted peridotites from the Yap Trench in the western Pacific Ocean have been studied for Re-Os elements and Re-Os isotopes. These peridotites have a low Re-Os content and variable 187Os/188Os ratios (0.12043–0.14867). The highest 187Os/188Os ratio is far higher than that of the primitive upper mantle and the lowest 187Os/188Os ratio is comparable to the most unradiogenic 187Os/188Os ratio (0.11933) discovered in subduction zone peridotites. The suprachondritic 187Os/188Os ratios of the Yap Trench peridotites results from modification of the mantle wedge by slab-derived fluid and melt. This is consistent with the observation that high 187Os/188Os ratios generally occur in oceanic peridotites with low Os content (<2 ppb) since Os may be reduced during late processes such as fluid alteration and melt refertilization. The sub-chondritic 187Os/188Os ratios of the Yap Trench peridotites correspond to a Re depletion age of 0.24–1.16 billion years, which means that these peridotites represent old mantle residue of ancient melting events. This ancient melting, combined with probable back-arc melting and forearc melting during subduction initiation, indicates that the Yap Trench mantle has a complex evolutionary history. The amount of old mantle residue in the oceanic asthenosphere was underestimated because the 187Os/188Os ratio in mantle peridotites is elevated during late processes. Therefore, old depleted mantle fragments may contribute substantially to the chemical heterogeneity of the oceanic mantle.

scholarly journals Discovery of Ancient Volcanoes in the Okhotsk Sea (Russia): New Constraints on the Opening History of the Kurile Back Arc Basin

Geosciences ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 442
Author(s):  
Reinhard Werner ◽  
Boris Baranov ◽  
Kaj Hoernle ◽  
Paul van den Bogaard ◽  
Folkmar Hauff ◽  
...  
Keyword(s):  
Trace Element ◽  
Island Arc ◽  
Kurile Island ◽  
Geochemical Data ◽  
Magma Source ◽  
Published Data ◽  
Kurile Island Arc ◽  
History Of ◽  
Spreading Rates ◽  
Back Arc

Here we present the first radiometric age and geochemical (major and trace element and isotope) data for samples from the Hydrographer Ridge, a back arc volcano of the Kurile Island Arc, and a newly discovered chain of volcanoes (“Sonne Volcanoes”) on the northwestern continental slope of the Kurile Basin on the opposite side of the arc. The 40Ar/39Ar age and geochemical data show that Hydrographer Ridge (3.2–3.3 Ma) and the “Sonne Volcanoes” (25.3–25.9 Ma) have very similar trace element and isotope characteristics to those of the Kurile Island Arc, indicating derivation from a common magma source. We conclude that the age of the “Sonne Volcanoes” marks the time of opening of the Kurile Basin, implying slow back arc spreading rates of 1.3–1.8 cm/y. Combined with published data from the Kurile fore arc, our data suggest that the processes of subduction, Kurile Basin opening and frontal arc extension occurred synchronously and that extension in the rear part and in the frontal part of the Kurile Island Arc must have been triggered by the same mechanism.

Geochemistry of the upper Snooks Arm Group basalts, Burlington Peninsula, Newfoundland: evidence against formation in an island arc

1980 ◽  
Vol 17 (7) ◽  
pp. 888-900 ◽  
Author(s):  
G. A. Jenner ◽  
B. J. Fryer
Keyword(s):  
Subduction Zone ◽  
Oceanic Crust ◽  
Sedimentary Rocks ◽  
Oceanic Islands ◽  
Oceanic Island ◽  
Island Arc ◽  
Geochemical Data ◽  
Basaltic Rocks ◽  
Arc Setting ◽  
Back Arc

The Snooks Arm Group of the Newfoundland Appalachians, which includes the Betts Cove ophiolite at its base, has been interpreted as oceanic crust overlain by island arc volcanic and sedimentary rocks. The limited geochemical data available on the upper Snooks Arm Group basalts have been used as evidence for and against their formation in an island arc environment.Reinvestigation of the chemistry of the basaltic rocks of the upper Snooks Arm Group establishes them as large ion lithophile enriched tholeiites. Similar basalts have been found in oceanic islands, on aseismic ridges, and possibly in back-arc basins. Chemically analogous rocks are notably lacking from island arc settings.The geochemistry and geology of the upper Snooks Arm Group suggest that these rocks may have formed in either an oceanic island setting or, as recently suggested by Upadhyay and Neale, as part of a marginal basin. It is not possible to distinguish between these alternate models, although the most similar basaltic rocks occur in the former environment. It is most unlikely that these rocks formed in an early island arc setting and indeed there may be no need for them to be associated with a major subduction zone.

Sign in / Sign up

Export Citation Format

Share Document