Age and significance of radiolarian sediments within basic extrusives of the marginal basin Guevgueli Ophiolite (northern Greece)

1996 ◽  
Vol 133 (2) ◽  
pp. 127-136 ◽  
Author(s):  
Taniel Danelian ◽  
Alastair H. F. Robertson ◽  
Sarantis Dimitriadis

AbstractWell-preserved Radiolaria have been discovered in calcareous silt turbidites and mudstones intercalated with basic extrusives of the Guevgueli Ophiolite, northern Greece. The mudstones contain terrigenous silt, probably derived from adjacent continental basement of the Serbo-Macedonian and/or Paikon units. Volcanic quartz and rare volcanic glass were probably derived from an active continental margin arc (Paikon volcanic arc) to the west. The radiolarian sediments were deposited within fault-controlled hollows in the ophiolitic extrusives, and then covered by massive and pillowed extrusives. The radiolarian assemblage is indicative of an early Late Jurassic (Oxfordian) age, which therefore dates the genesis of the Guevgueli Ophiolite. Our data are consistent with the age of the intrusive Late Jurassic Fanos Granite, believed to be contemporaneous with the Guevgueli Ophiolite. In general, the Guevgueli and related ophiolites of northern Greece are thought to have formed within a transtensional intra-continental marginal basin, generated in response to oblique eastward subduction of older Tethyan oceanic crust (Almopias ocean).

2012 ◽  
Vol 524-527 ◽  
pp. 16-23
Author(s):  
Jian Guo Huang ◽  
Run Sheng Han ◽  
Ren Tao ◽  
Zhi Qiang Li

The Late Triassic Tumugou Formation volcanic rocks which belongs to typical island arc volcanic rocks in southern end of Yidun island arc belt is located at the eastern of the Zhongdian ,NW Yunnan, SW China. The volcanic rocks can be divided into three categories:andesitic basalt, andesite, quartz andesite, etc. Through geochemical analysis the major elements, rare earth ele and trace element in volcanic rocks, SiO255.18-57.59×10-2,TiO21.16-1.45×10-2,Na2O+K2O5.11-8.05×10-2.consider it is calc-alkaline- alkaline Series of high-K andesite, volcanic may be controlled by the crystal fractionation of magma.Rb31.50-101×10-6,Ba1310-12300×10-6,Nb/Ta11.4-15.5,REE166.07-240.78×10-6,δEu0.74-1.00,REE distribution patterns show oblique to the HREE side and enrichment in LREE .Eu anomaly is not obvious. It is can see from the relevant figure about trace element, it is very similar in magmatic distribution patterns between volcanic rock and Volcanic-arc rock, indicating that the volcanic in this area may be formed in volcanic-arc environment. From east to west, Magma source depth have regular change with the really thickness of mainland shell. Explain that Tumugou Formation volcanic rock is subduction by Ganzi- Litang Ocean basin from east to west. Hongshan-Ousaila region of eastern edge of Zhongdian is the volcanic island arc system during the passive continental margin into an active continental margin.


2014 ◽  
Vol 50 ◽  
pp. 155
Author(s):  
Sandra M. Barr ◽  
Cameron J. Bartsch ◽  
Brent V. Miller ◽  
Chris E. White

The Beaver Harbour Porphyry is a high-level intermediate to felsic granitoid and locally tuffaceous unit with quartz and less abundant feldspar phenocrysts. It forms a fault-bound sliver along the southern margin of the New River belt in southern New Brunswick. A concordant TIMS U-Pb (zircon) age of 551 ± 1.2 Ma shows that the porphyry is of the same age as other high-level plutonic and volcanic units that form most of the New River belt. Chemical data show that these units likely formed in a volcanic-arc environment at an active continental margin. One sample from the porphyry has ƐNd(t) of -0.5, within the range of other samples from the New River belt and consistent with the interpretation that the belt is part of Ganderia, rather than Avalonia, which generally has more juvenile isotopic signatures.


2014 ◽  
Vol 41 (3) ◽  
pp. 207-215 ◽  
Author(s):  
Ali Sepahi ◽  
Hossein Shahbazi ◽  
Wolfgang Siebel ◽  
Ahmad Ranin

Abstract The Sanandaj-Sirjan zone of Iran is a metamorphic belt consisting of rocks which were metamorphosed under different pressure and temperature conditions and intruded by various plutons ranging in composition from gabbro to granite. The majority of these granitoids formed along the ancient active continental margin of the Neo-Tethyan ocean at the southeastern edge of the central Iranian microplate. Geochronological data published in recent years indicate periodic plutonism lasting from Carboniferous through Mesozoic to late-Paleogene times (from ca. 300 to ca. 35 Ma) with climax activity during the mid- and late-Jurassic. The age constraints for plutonic complexes, such as Siah-Kouh, Kolah-Ghazi, Golpayegan (Muteh), Azna, Aligoodarz, Astaneh, Borujerd, Malayer (Samen), Alvand, Almogholagh, Ghorveh, Saqqez, Marivan, Naqadeh and Urumieh, clearly indicate the periodic nature of magmatism. Therefore, the Sanandaj-Sirjan zone preserves the record of magmatic activity of a complete orogenic cycle related to (1) Permocarboniferous(?) rifting of Gondwana and opening of the Neo-Tethyan ocean, (2) subduction of the oceanic crust, (3) continental collision and (4) post-collision/post-orogenic activities. The formation of the Marivan granitoids, northwestern Sanandaj-Sirjan zone, for which we present U-Pb zircon and titanite ages of ca. 38 Ma, can be related to the collisional and post-collisional stages of this orogenic cycle.


2013 ◽  
Vol 734-737 ◽  
pp. 476-479
Author(s):  
Yue Qiao Zhang ◽  
Wei Hou ◽  
Fang Zhang

The provenance tectonic background of Late Jurassic Mohe Basin was researched through the geochemical composition of sandstone. The Late Jurassic Mohe Basin is characterized by multiple provenances. One provenance is the active continental margin, and another is the island arc. Comparing with the regional lithology, the active continental margin may be from the Mongolia-Okhotsk orogenic belt, and the island arc may be from the northern of the Da Hingan Mountains. The characteristics are concerned with its geotectonic position.


2019 ◽  
Vol 46 (3) ◽  
pp. 526
Author(s):  
Carlos Dino Ramacciotti ◽  
César Casquet ◽  
Edgardo Gaspar Baldo ◽  
Sebastián Osvaldo Verdecchia ◽  
Matías Martín Morales ◽  
...  

The Sierra de Pie de Palo (SPP, Western Sierras Pampeanas) shows evidence of two regional metamorphisms: one Mesoproterozoic attributed to the Grenvillian orogeny and other of Ordovician age related to the Famatinian orogeny. The Neoproterozoic-to-Cambrian sedimentary successions that cover the Grenvillian basement only record the Ordovician event. One staurolite-schist from the Ediacaran Difunta Correa Metasedimentary Sequence collected in the southeastern side of the SPP allows to constrain, by means of pseudosections, a prograde evolution from ca. 3 kbar and 515 ºC up to ca. 9 kbar and 640 ºC corresponding to a high P/T gradient. The SPP and the immediately east Loma de Las Chacras outcrop were part of the famatinian forearc which shows a progressive decrease of P (from ca. 13 kbar to 6 kbar), T (from ca. 900 ºC to 450 ºC), and P/T gradient (from ca. 85 ºC/kbar to 35 ºC/kbar) towards the active continental margin on the west. The Caucete Group, in the western side of the SPP, represents the westernmost part of the forearc, near to the active continental margin. Metamorphism was apparently coeval with the Famatinian magmatism and with ductile underthrusting at ca. 470-465 Ma, which led to burial of the forearc beneath the magmatic arc.


Author(s):  
A. V. Ryazantsev ◽  
L. A. Novikov ◽  
A. A. Razumovskij

In the West of the aHochthon of Magnitogorsk zone thrusted onto the Precambrian complexes of the Uraltau zone, the Devonian island-arc complexes overlap stratigraphicalry the Ordovician and Silurian chert-basalt sequences and serpentine melange. Melange and Ordovician strata are intruded by dyke swarms and sheeted dykes («dyke in dyke») which are composed of mafic and ultramafic rocks. The dykes, composed by gabbro-dolerite, amphibole K-feldspar gabbro, hornblendite, picrite and lamprophyre, predominate. The composition of the ultramafic rocks corresponds to the composition of picrite and komatiite. The 40Ar/39Ar age of the magmatic amphibole from gabbro is 357 ± 8 m.y. The formation of dykes is related to the Early Carboniferous rift-related magmatism on an active continental margin.


1982 ◽  
Vol 22 (1) ◽  
pp. 283 ◽  
Author(s):  
J. J. Veevers ◽  
J. G. Jones ◽  
C. McA. Powell

Two morphotectonic features dominated the development of Australia's Phanerozoic sedimentary basins: a rifted arch on the divergent western and southern margins, such as exists today in East Africa-Arabia, and a volcanic arc on the convergent eastern margin, such as the present Andaman-Sumatran Arc. A presumed rifted-arch system, associated on one side with the growth of the Tethyan Ocean and on the other with failed arms, developed in northwest Australia from the beginning of the Phanerozoic. A second system developed in the same area and extended southward between Greater India and Australia in the Late Carboniferous and evolved in the Late Jurassic and Early Cretaceous into the eastern Indian Ocean. Also in the Late Jurassic a rifted-arch system developed along the southern margin between Antarctica and Australia and in the Late Cretaceous evolved into the southeast Indian Ocean. On both margins the rifted-arch system was succeeded for some 30 to 40 Ma by rim basins confined between the continent and an uplifted rim alongside the continent-ocean boundary, so that restricted marine sediment was deposited over a terrain of rift-valley fluvial sediment cut into fault blocks in a configuration favourable to petroleum accumulation. In the Ceduna Plateau depocentre of the Great Australian Bight Basin a very thick rim basin was deposited in a saddle of the rifted-arch system from a copious provenance in the ancestral Eastern Highlands. On both margins the rim basins were overlain by open marine deposits, mainly carbonate, of varying thickness.The convergent eastern margin started also at the beginning of the Phanerozoic, and developed through marginal sea opening and filling behind an island arc; widespread deformation then followed, and led in the Early Silurian to the development of a basin-and- range terrain. In the Late Devonian, a volcanic arc appeared along the continental margin, and subsequently jumped eastward twice to the mid-Cretaceous. The succession of jumps generated a vertical sequence of basins that at any one time existed side by side, so that the fore-arc basin is overlain by the foreland, in turn overlain by the pericratonic basin. The foreland and pericratonic basins, on the landward side of the volcanic arc, received volcanogenic sediment, prone to be marine, from the arc, and quartzose sediment, prone to be fluvial, from the craton; the foreland basin was subjected to shearing from transcurrent motion along the arc, so that growth structures provided receptacles for petroleum generated by heat flow from the arc. The marginal marine volcanogenic sediment was the main source and the interfingering fluvial quartz sand the reservoir.Three tectonic regimes can be recognized, and are characterized by intervals of relatively constant latitude, climate, depositional facies, and plate configuration. A Pre-Gondwanan regime, 570 to 320 Ma ago, of low latitude, started with plate divergence on the northwest and convergence on the east, and ended with widespread deformation in the east and centre, of an age and kind similar to that affecting the ancestral Rocky Mountains of North America. A Gondwanan regime, from 320 to 95 Ma, of high latitude, with rare evaporites and carbonates, started with a rift-valley system along the western margin that developed into the Indian Ocean 160 to 125 Ma ago, and an arc jump on the east; and ended with the separation of Antarctica and Australia (by the splitting of a rifted arch) on the south, and of Australia and Lord Howe Rise (by the splitting of an arc) on the east. A Post-Gondwanan regime, 95 to 0 Ma ago, of diminishing latitude, has restored carbonates to Australia along its divergent margins, and in the north, in New Guinea, a continental margin volcanic arc, similar to the Gondwanan arcs, has led to uplift in the Neogene.


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