scholarly journals EAST VARDAR OPHIOLITES REVISITED: A BRIEF SYNTHESIS OF GEOLOGY AND GEOCHEMICAL DATA

2018 ◽  
Vol 39 (1) ◽  
pp. 51 ◽  
Author(s):  
Blažo Boev ◽  
Vladica Cvetković ◽  
Dejan Prelević ◽  
Kristina Šarić ◽  
Ivan Boev
Keyword(s):  
Upper Jurassic ◽  
Geochemical Data ◽  
Exact Nature ◽  
Spreading Ridge ◽  
Ridge Axis ◽  
Volcanic Arc ◽  
Origin And Evolution ◽  
Tectonic Reconstruction ◽  
Intrusive Rocks ◽  
Back Arc

The study reports and synthesizes the available geological and geochemical data on the East Vardar ophiolites comprising most known occurrences from the South Apuseni Mountains in Romania to the tip of the Chalkidiki Pen-insula in Greece. The summarized geological data suggest that the East Vardar ophiolites are mostly composed of the magmatic sequences, whereas the mantle rocks are very subordinate. The members of the magmatic sequences are characterized by the presence of abundant acid and intermediate volcanic and intrusive rocks. The age of these ophio-lites is paleontologically and radiometrically constrained and these data suggest that the East Vardar ophiolite formed as a short-lived oceanic realm that was emplaced before the uppermost Kimmeridgian. A relatively weak adakitic affinity is shown by intra-ophiolitic acid and intermediate rocks in many East Vardar provinces. It can be taken as evidence that the subduction of the young and hot slab, most likely along the earlier spreading ridge has occurred. A paleo-tectonic reconstruction consisting of four stages is proposed. It involves: a) an early/mid-Jurassic north-northeastward subduction of the West Vardar oceanic plate; b) the formation of a mid-Jurassic volcanic arc and a narrow back-arc oceanic stripe of East Vardar behind it; c) the mid-/Upper Jurassic initiation of East Vardar subduc-tion along the ridge axis, and d) complex and heterogeneous emplacement of the East Vardar ophiolites. So far avail-able data allow for having relatively clear ideas about the origin and evolution of the East Vardar ophiolites. Howev-er, in order to provide better understanding of all aspects of its evolution we need to answer additional questions re-lated to the true structural position of the East Vardar ophiolites slices in Serbia, the exact nature of subduction that caused back-arc spreading (intraoceanic vs subduction under continent?) and the full significance of the adakitic sig-nature shown by rocks in the East Vardar provinces other than Demir Kapija.

scholarly journals Structure of oceanic crust in back-arc basins modulated by mantle source heterogeneity

Geology ◽  
2020 ◽  
Author(s):  
Ingo Grevemeyer ◽  
Shuichi Kodaira ◽  
Gou Fujie ◽  
Narumi Takahashi
Keyword(s):  
Oceanic Crust ◽  
Mantle Source ◽  
Seismic Data ◽  
Lower Crust ◽  
Subduction Zones ◽  
P Wave ◽  
Spreading Ridge ◽  
Volcanic Arc ◽  
Depleted Mantle ◽  
Back Arc

Subduction zones may develop submarine spreading centers that occur on the overriding plate behind the volcanic arc. In these back-arc settings, the subducting slab controls the pattern of mantle advection and may entrain hydrous melts from the volcanic arc or slab into the melting region of the spreading ridge. We recorded seismic data across the Western Mariana Ridge (WMR, northwestern Pacific Ocean), a remnant island arc with back-arc basins on either side. Its margins and both basins show distinctly different crustal structure. Crust to the west of the WMR, in the Parece Vela Basin, is 4–5 km thick, and the lower crust indicates seismic P-wave velocities of 6.5–6.8 km/s. To the east of the WMR, in the Mariana Trough Basin, the crust is ~7 km thick, and the lower crust supports seismic velocities of 7.2–7.4 km/s. This structural diversity is corroborated by seismic data from other back-arc basins, arguing that a chemically diverse and heterogeneous mantle, which may differ from a normal mid-ocean-ridge–type mantle source, controls the amount of melting in back-arc basins. Mantle heterogeneity might not be solely controlled by entrainment of hydrous melt, but also by cold or depleted mantle invading the back-arc while a subduction zone reconfigures. Crust formed in back-arc basins may therefore differ in thickness and velocity structure from normal oceanic crust.

scholarly journals ORIGIN AND EVOLUTION OF THE OPHIOLITIC COMPLEX OF ZDRALJICA (CENTRAL SERBIA)

2004 ◽  
Vol 36 (1) ◽  
pp. 597
Author(s):  
K. Resimic-Saric ◽  
A. Koroneos ◽  
V. Cvetkovic ◽  
K. Balogh
Keyword(s):  
Partial Melting ◽  
Fractional Crystallization ◽  
Upper Jurassic ◽  
Geochemical Data ◽  
Spinel Lherzolite ◽  
Origin And Evolution ◽  
Variation Patterns ◽  
One Step ◽  
Ophiolitic Complex ◽  
Batch Melting

The ophiolitic complex of Zdraljica (Central Serbia) belongs to the Eastern Branch of the Vardar suture zone. It was emp'aced during the Upper Jurassic. The complex consists predominately of a MORB/VAB-like tholeiitic suite, represented mostly by gabbros and diabases. Small occurrences of cummulitic peridotites, basalts and plagiogranites also appear. The tholeiitic suite is intruded by calc-alkaline intermediate and acid magmas. Geochemical data suggest that the ZOC tholeiitic rocks originated by partial melting of a spinel-lherzolite source. Non-modal batch melting modeling indicates 10 to 15 % of partial melting of such a source. The magmas were later modified by fractional crystallization. One-step major element modeling requires 40% (F=0.60) of fractional crystallization of a mineral assemblage: PI52 gCpxi2 5OI26 iTtn2 9Ap4.4Mgt1.0- The model is supported by the variation patterns of most trace elements.

scholarly journals The Petrology, Geochemistry and Geochronology of Back-Arc Stratovolcanoes in the Southern Kermadec Arc-Havre Trough, SW Pacific

2021 ◽  
Author(s):  
◽  
Alexander Zohrab
Keyword(s):  
Trace Element ◽  
Fractional Crystallisation ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Rock Composition ◽  
Volcanic Arc ◽  
Phenocryst Assemblage ◽  
Origin And Evolution ◽  
Depleted Mantle ◽  
Back Arc

<p>The Kermadec Arc-Havre Trough (KAHT) is widely regarded as a classical example of an intra-oceanic arc-back-arc system, where subduction-driven arc magmatism is focused at the Kermadec volcanic arc-front, and magmatism within the Havre Trough back-arc system results from decompression-related melting. In detail, however, the Havre Trough has not been well-studied, and data for very few lavas have been reported.  Recent mapping undertaken in the southern Havre Trough has resulted in the discovery of several prominent submarine stratovolcanoes, Gill Seamount, Rapuhia Seamount and the related Rapuhia Ridge, Yokosuka Seamount, and Giljanes Seamount, situated in the middle of deep rifts and on elevated crustal plateaux. The origin and evolution of these stratovolcanoes is unknown. The first detailed dataset of whole rock major and trace element geochemistry, mineral chemistry, and ⁴⁰Ar/³⁹Ar isotope data, for lavas erupted from these volcanoes is presented here, and used to investigate the processes that drive volcanism in the Havre Trough back-arc.  ⁴⁰Ar/³⁹Ar ages obtained from back-arc stratovolcanoes range from ca. 1167 - 953 ka for Gill Seamount, and ca. 107 - 50 ka for Rapuhia Ridge. These ages overlap with known ages for arc-front lavas, indicating that both back-arc and arc-front volcanism are coeval. These ages are all significantly younger than the inferred initation of Havre Trough rifting ca. 5 - 6 Ma.  Lavas analysed from Gill Seamount and Rapuhia Ridge are basaltic to basaltic-andesitic in whole rock composition and contain a phenocryst assemblage of olivine ± orthopyroxene + clinopyroxene ± plagioclase. Lavas from Rapuhia Seamount, Yokosuka Seamount and Giljanes Seamount range from andesitic to dacitic in composition, and have a phenocryst assemblage consisting primarily of plagioclase ± clinopyroxene ± amphibole ± Fe-Ti oxides ± apatite. Variations in mineral assemblages and whole rock compositions of the lavas are consistent with crystal fractionation of their respective phenocryst phases. The more evolved compositions of Rapuhia Seamount, Yokosuka Seamount and Giljanes Seamount, all sited on an elevated crustal plateau, are inferred to result from prolonged assimilation + fractional crystallisation (AFC) in the mid- to upper- crust.  Mineral compositions provide additional evidence for fractional crystallisation, and most crystals are inferred to have crystallised in equilibrium with their host melt. However, compositions of some olivine phenocrysts in Gill Seamount and Rapuhia Ridge indicate multiple populations of olivine, suggesting their magmatic systems were open to contributions from secondary processes. Variations in Or content in plagioclase crystals for a given lava suite suggests the sample suites crystallised from melts with different starting K₂O compositions.  Elevated ratios of Nb/Yb in the mafic Gill Seamount and Rapuhia Ridge lavas indicate the back-arc volcanoes and ridges originated from a less depleted mantle than that present underneath the Kermadec volcanic arc-front, likely a consequence of trenchward advection of mantle within a suprasubduction wedge and/or partial melting of a fusible enriched mantle component.   All whole rock samples from these back-arc volcanoes have trace element characteristics that resemble those of typical volcanic arc magmas, indicating that they are variably modified by subducting plate-derived components despite their rear-arc setting. However, the extent of fluid enrichment is less than that at the Kermadec volcanic arc-front. Elevated REE patterns and (La/Sm)N ratios suggest the subduction-component modifying back-arc volcano magmas is dominated by subducting sediment. This sediment component is not consistent with aqueous fluid transfer or bulk mixing, but by the addition of a sediment-derived partial melt with residual accessory phases monazite + zircon + rutile. HFSE/REE fractionated trace element patterns overlap for unmodified basalts from Gill Seamount and Rapuhia Ridge, and Rumble V Ridge back-arc constructional volcanism to the south. This suggests that a similar mechanism triggers constructional back-arc volcanism at both locations in the southern Havre Trough, likely a consequence of thermal anomalies inferred to be present in the mantle wedge (Todd et al. (2011)).</p>

scholarly journals The Petrology, Geochemistry and Geochronology of Back-Arc Stratovolcanoes in the Southern Kermadec Arc-Havre Trough, SW Pacific

2021 ◽  
Author(s):  
◽  
Alexander Zohrab
Keyword(s):  
Trace Element ◽  
Fractional Crystallisation ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Rock Composition ◽  
Volcanic Arc ◽  
Phenocryst Assemblage ◽  
Origin And Evolution ◽  
Depleted Mantle ◽  
Back Arc

<p>The Kermadec Arc-Havre Trough (KAHT) is widely regarded as a classical example of an intra-oceanic arc-back-arc system, where subduction-driven arc magmatism is focused at the Kermadec volcanic arc-front, and magmatism within the Havre Trough back-arc system results from decompression-related melting. In detail, however, the Havre Trough has not been well-studied, and data for very few lavas have been reported.  Recent mapping undertaken in the southern Havre Trough has resulted in the discovery of several prominent submarine stratovolcanoes, Gill Seamount, Rapuhia Seamount and the related Rapuhia Ridge, Yokosuka Seamount, and Giljanes Seamount, situated in the middle of deep rifts and on elevated crustal plateaux. The origin and evolution of these stratovolcanoes is unknown. The first detailed dataset of whole rock major and trace element geochemistry, mineral chemistry, and ⁴⁰Ar/³⁹Ar isotope data, for lavas erupted from these volcanoes is presented here, and used to investigate the processes that drive volcanism in the Havre Trough back-arc.  ⁴⁰Ar/³⁹Ar ages obtained from back-arc stratovolcanoes range from ca. 1167 - 953 ka for Gill Seamount, and ca. 107 - 50 ka for Rapuhia Ridge. These ages overlap with known ages for arc-front lavas, indicating that both back-arc and arc-front volcanism are coeval. These ages are all significantly younger than the inferred initation of Havre Trough rifting ca. 5 - 6 Ma.  Lavas analysed from Gill Seamount and Rapuhia Ridge are basaltic to basaltic-andesitic in whole rock composition and contain a phenocryst assemblage of olivine ± orthopyroxene + clinopyroxene ± plagioclase. Lavas from Rapuhia Seamount, Yokosuka Seamount and Giljanes Seamount range from andesitic to dacitic in composition, and have a phenocryst assemblage consisting primarily of plagioclase ± clinopyroxene ± amphibole ± Fe-Ti oxides ± apatite. Variations in mineral assemblages and whole rock compositions of the lavas are consistent with crystal fractionation of their respective phenocryst phases. The more evolved compositions of Rapuhia Seamount, Yokosuka Seamount and Giljanes Seamount, all sited on an elevated crustal plateau, are inferred to result from prolonged assimilation + fractional crystallisation (AFC) in the mid- to upper- crust.  Mineral compositions provide additional evidence for fractional crystallisation, and most crystals are inferred to have crystallised in equilibrium with their host melt. However, compositions of some olivine phenocrysts in Gill Seamount and Rapuhia Ridge indicate multiple populations of olivine, suggesting their magmatic systems were open to contributions from secondary processes. Variations in Or content in plagioclase crystals for a given lava suite suggests the sample suites crystallised from melts with different starting K₂O compositions.  Elevated ratios of Nb/Yb in the mafic Gill Seamount and Rapuhia Ridge lavas indicate the back-arc volcanoes and ridges originated from a less depleted mantle than that present underneath the Kermadec volcanic arc-front, likely a consequence of trenchward advection of mantle within a suprasubduction wedge and/or partial melting of a fusible enriched mantle component.   All whole rock samples from these back-arc volcanoes have trace element characteristics that resemble those of typical volcanic arc magmas, indicating that they are variably modified by subducting plate-derived components despite their rear-arc setting. However, the extent of fluid enrichment is less than that at the Kermadec volcanic arc-front. Elevated REE patterns and (La/Sm)N ratios suggest the subduction-component modifying back-arc volcano magmas is dominated by subducting sediment. This sediment component is not consistent with aqueous fluid transfer or bulk mixing, but by the addition of a sediment-derived partial melt with residual accessory phases monazite + zircon + rutile. HFSE/REE fractionated trace element patterns overlap for unmodified basalts from Gill Seamount and Rapuhia Ridge, and Rumble V Ridge back-arc constructional volcanism to the south. This suggests that a similar mechanism triggers constructional back-arc volcanism at both locations in the southern Havre Trough, likely a consequence of thermal anomalies inferred to be present in the mantle wedge (Todd et al. (2011)).</p>

scholarly journals Southern Central Andes Neogene magmatism over the Pampean Flat Slab: implications on crustal and slab melts contribution to magma generation in Precordillera, Western Argentina

2017 ◽  
Vol 44 (3) ◽  
pp. 249 ◽  
Author(s):  
Stella Poma ◽  
Adriana Ramos ◽  
Vanesa D. Litvak ◽  
Sonia Quenardelle ◽  
Emma B. Maisonnave ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Central Andes ◽  
Progressive Increase ◽  
Geochemical Data ◽  
Transitional Region ◽  
Continuous Increase ◽  
Volcanic Arc ◽  
Age Variations ◽  
Southern Central ◽  
Back Arc

A Miocene to Pliocene (13 to 4.6 Ma) mostly pyroclastic sequence is exposed along the Iglesia Valley, to the east of the former main volcanic arc. This area is a transitional region between Cordillera Frontal and Precordillera, over the f lat slab segment of the Southern Central Andes, at 29º30’ S to 30º00’ S. New radiometric ages, geochemical data, petrography and field relationships are evaluated to establish differences and similarities between Miocene arcrelated sequences across the main arc and its expansion towards a back arc position, in western Precordillera. Analyzed rocks have a magmatic arc signature partially like the former main volcanic arc to the west. The Iglesia Valley rocks are LREE-enriched (La/Sm: 3.7-6.5) with respect to HREE (Sm/Yb: 2.2-6.0) and define patterns with a pronounced slope. Sm/Yb ratios generally increase with time, as pressures increase, with retention of HREE in residual mineralogy, particularly garnet at Sm/Yb>4. Volcanic activity in Cordillera Frontal and the volcanic-volcaniclastic expression in Precordillera show a continuous increase in the La/Yb ratio with decreasing age. Variations in the residual mineralphase equilibrating with magmas would be related to the progressive increase in crustal thickness due to the tectonic compressive regime resulting from shallow subduction since Middle Miocene. The data presented suggest that the arc magmatic activity during the Miocene was expanded notably to the East in relation to the location of the main arc at Valle del Cura, in Cordillera Frontal. The extensive amplitude of the volcanic arc activity is indicative of the slab gradual f lattening. Particularly, the mantle-derived magmas from Lomas del Campanario Formation (Western Precordillera) are enriched by subduction related f luids but also by crustal components. It is interpreted that the cause of the geochemical differences between the back arc position rocks and the main arc lay in the heterogeneous composition of the underlying continental crust involved in both locations. Presence of volcanic rocks with adakitic geochemical affinity probably ref lect astenospheric-derived melts that interacted through a heterogeneous and thickened crust toward the surface.

Silicic magmas of Protector Shoal, South Sandwich arc: indicators of generation of primitive continental crust in an island arc

2006 ◽  
Vol 144 (1) ◽  
pp. 179-190 ◽  
Author(s):  
P. T. LEAT ◽  
R. D. LARTER ◽  
I. L. MILLAR
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Early Stage ◽  
Geochemical Data ◽  
The South ◽  
Volcanic Arc ◽  
Silicic Volcanic ◽  
South Sandwich Islands ◽  
Silicic Magmas ◽  
Back Arc

Protector Shoal, the northernmost and most silicic volcano of the South Sandwich arc, erupted dacite–rhyolite pumice in 1962. We report geochemical data for a new suite of samples dredged from the volcano. Geochemically, the dredge and 1962 samples form four distinct magma groups that cannot have been related to each other, and are unlikely to have been related to a single basaltic parent, by fractional crystallization. Instead, the silicic rocks are more likely to have been generated by partial melting of basaltic lower crust within the arc. Trace element and Sr–Nd isotope data indicate that the silicic volcanics have compositions that are more similar to the volcanic arc than the oceanic basement formed at a back-arc spreading centre, and volcanic arc basalts are considered to be the likely source for the silicic magmas. The South Sandwich Islands are one of several intra-oceanic arcs (Tonga–Kermadec, Izu–Bonin) that have: (1) significant amounts of compositionally bimodal mafic–silicic volcanic products and (2) 6.0–6.5 km s−1P-wave velocity layers in their mid-crusts that have been imaged by wide-angle seismic surveys and interpreted as intermediate-silicic plutons. Geochemical and volume considerations indicate that both the silicic volcanics and plutonic layers were generated by partial melting of basaltic arc crust, representing an early stage in the fractionation of oceanic basalt to form continental crust.

Deep Structure and Active Tectonics of the South Aegean Volcanic Arc

Elements ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 153-158 ◽  
Author(s):  
Costas B. Papazachos
Keyword(s):  
Deep Structure ◽  
Active Tectonics ◽  
Aegean Sea ◽  
Low Velocity ◽  
Volcanic Arc ◽  
High Attenuation ◽  
Global Positioning ◽  
Back Arc ◽  
The Impact ◽  
Subducting Slab

The seismotectonic setting of the Aegean Sea, based on information from seismicity, neotectonics and global positioning system studies, is characterized by a sharp transition from a compressional outer arc to a complex back-arc, with an approximate north–south extension along the volcanic arc. Seismicity and 3-D tomography studies reveal the geometry of the subducting slab and image the low-velocity/high-attenuation mantle wedge at depths of 50–80 km beneath the volcanic arc where magma is generated. The 1956 Amorgos M7.5 earthquake and the impact from its seismic shaking and landslide-triggered tsunamis are discussed in the context of the regional seismotectonic setting.

scholarly journals The Origin of Back-Arc Spreading in The Eastern Edge of Scotia Plate

2016 ◽  
Vol 5 (1) ◽  
pp. 21
Author(s):  
Indra Budi Prasetyawan
Keyword(s):  
Subduction Zones ◽  
Sandwich Plate ◽  
Magnetic Anomalies ◽  
South American ◽  
The South ◽  
Origin And Evolution ◽  
Bathymetric Data ◽  
Scotia Ridge ◽  
Back Arc ◽  
Eastern Edge

The origin and evolution of  back-arc spreading in the eastern edge of Scotia Plate will be discussed in this paper. The Scotia Plate is a tectonicplate on the edge of the South Atlantic and Southern Ocean, located between the South American and Antartic plates. The East Scotia Ridge (ESR) in the eastern edge of Scotia Plate, forned due to subduction of the South American plate beneath the South Sandwich plate along the South Sandwich Island arc. The methods and techniques of data acquisition used were data from absolution motions and data from magnetic anomalies and bathymetric data. Magnetic anomalies and  bathymetric data that used in this paper consist of two sets data. First, magnetic anomalies and  bathymetric data which were obtained by aboard HMS Endurance in the 1969-70 austral summer, and the second, magnetic anomalies and  bathymetric data which were obtained after removal of the International Geomagnetic Reference Field (IGRF). Absolution motion analyses in the subduction zones of Sandwich plate results that form back-arc spreading in East Scotia Ridge showing high deformation for slow moving upper plates. Where back-arc spreading is associated with upper plate retreat that reaches 26.9 mm/year and have back-arc deformation style consistent with upper plate absolute. Key Words: Geological oceanography, Scotia plate, back-arc spreading

Geochemistry of Sainte-Marguerite volcanic rocks: implications for the evolution of Silurian–Devonian volcanism in the Gaspé Peninsula

2008 ◽  
Vol 45 (1) ◽  
pp. 15-29 ◽  
Author(s):  
Alan D’hulst ◽  
Georges Beaudoin ◽  
Michel Malo ◽  
Marc Constantin ◽  
Pierre Pilote
Keyword(s):  
Lower Devonian ◽  
Volcanic Rocks ◽  
Magma Source ◽  
Volcanic Arc ◽  
Lower Silurian ◽  
Trace Element Signature ◽  
Arc Setting ◽  
Back Arc ◽  
Gaspe Peninsula ◽  
Gaspé Peninsula

The Lower Devonian Sainte-Marguerite volcanic rocks are part of a Silurian–Devonian volcanic sequence deposited between the Taconian and Acadian orogenies in the Gaspé Peninsula, Quebec, Canada. The Sainte-Marguerite unit includes basaltic and dacitic lava flows with calc-alkaline and volcanic-arc affinities. Such affinities are also recorded by the trace-element signature in Lower Silurian and most Lower Devonian volcanic units of the Gaspé Peninsula. However, most of the other Silurian–Devonian volcanic rocks occurring in the Gaspé Peninsula have been previously interpreted to have erupted in an intracontinental setting. A back-arc setting for the Gaspé Peninsula between the Taconian and Acadian orogenies could account for these subduction volcanic-arc signatures, though a metasomatized lithospheric mantle magma source, unrelated to subduction, cannot be excluded. Lower Silurian and Lower Devonian volcanic rocks in the central part of the Gaspé Peninsula show an arc affinity, whereas Upper Silurian and Lower to Middle Devonian volcanic rocks, located in the south and north of the Gaspé Peninsula, respectively, show a within-plate affinity. The Lower Devonian Archibald Settlement and Boutet volcanic rocks of the southern and northern Gaspé Peninsula, respectively, show a trend toward a within-plate affinity. This suggests that within-plate volcanism migrated from south to north through time in an evolving back-arc environment and that the subduction signature of Lower Silurian and Lower Devonian rocks results from a source that melted only under the central part of the Gaspé Peninsula.

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