Ophiolitic rocks and evidence for hydrothermal convection of sea water within oceanic crust

1979 ◽  
pp. 429-431 ◽  
Author(s):  
E. T. C. Spooner
Keyword(s):  
Oceanic Crust ◽  
Sea Water ◽  
Hydrothermal Convection ◽  
Ophiolitic Rocks

The lead and strontium isotope geochemistry of metalliferous sediments associated with Upper Cretaceous ophiolitic rocks in Cyprus, Syria, and the Sultanate of Oman

1981 ◽  
Vol 18 (8) ◽  
pp. 1290-1302 ◽  
Author(s):  
N. H. Gale ◽  
E. T. C. Spooner ◽  
P. J. Potts
Keyword(s):  
Trace Element ◽  
Oceanic Crust ◽  
Late Cretaceous ◽  
Upper Cretaceous ◽  
Sea Water ◽  
Isotope Ratios ◽  
Strontium Isotope ◽  
Sultanate Of Oman ◽  
Metalliferous Sediments ◽  
Ophiolitic Rocks

Metalliferous sediments consisting dominantly of fine-grained iron and manganese oxides and hydroxyoxides have been widely recorded from the crests of sea-floor spreading ridges and as a basal facies of the sediment accumulations of the oceanic crust. Similar sedimentary rocks that, in Cyprus, for example, contain 10–44 wt.% Fe and 2–16 wt.% Mn, occur in association with ophiolitic rocks. These chemical precipitates are thought to have formed by oxidation of hydrothermal fluid released in submarine hot-spring areas in the discharge zones of ocean-floor geothermal systems that contained convectively circulating sea water.Lead isotope ratios of 18 samples associated with Upper Cretaceous ophiolitic rocks of the Troodos massif, Cyprus (6 samples), the Baër-Bassit area, Syria (6), and the Semail nappe in the Sultanate of Oman (6), indicate that the metalliferous sediments contain lead leached from the underlying basaltic oceanic crust during hot water – rock interaction. The amount of basaltic lead varies from comparatively little, in some samples from Syria, to essentially 100% in many of the samples from Oman. Linear mixing relationships characterized by correlation coefficients of 0.97 and 0.86 are defined on 208Pb/204Pb–206Pb/204Pb and 207Pb/204Pb–206Pb/204Pb diagrams. The mixing lines connect the less radiogenic mid-ocean ridge basalt field with the more radiogenic sea-water lead field of manganese nodules, which is also the average isotopic composition of continental crustal material. Negative covariations with Th, a trace element index of the detrital sedimentary component, and Pb/Fe, a monitor of diagenetic addition of Pb from pore waters, suggest that the main cause of the lead isotopic variation was initial adsorption of a variable ratio of leached basaltic lead to dissolved sea-water lead.The mean of 13 initial 87Sr/86Sr ratios (0.7079 ± 0.0013; 2 SD) is statistically indistinguishable from the estimated 87Sr/86Sr ratio for Late Cretaceous sea water at 0.7076 ± 0.0006 (25 values; Peterman et al.). Hence, strontium was largely derived by adsorption from sea water. However, three determinations are significantly more radiogenic than Late Cretaceous sea water. A statistically significant covariation with Rb (r = 0.78), one of the trace elements contained in the detrital, sedimentary component, suggests that the increase was caused by a variable admixture of terrigenous material.Neither lead nor strontium isotope ratios nor trace element concentrations suggest significant diagenetic modification of the isotopic compositions of the metalliferous sediments.

Eclogitic rocks in the St. Cyr klippe, Yukon, and their tectonic significance

1992 ◽  
Vol 29 (6) ◽  
pp. 1296-1304 ◽  
Author(s):  
Philippe Erdmer
Keyword(s):  
High Pressure ◽  
Oceanic Crust ◽  
North American ◽  
Suture Zone ◽  
Late Paleozoic ◽  
The North ◽  
Tectonic Significance ◽  
Subducted Oceanic Crust ◽  
Ophiolitic Rocks ◽  
Subducting Slab

Until recently, the Nisutlin allochthonous assemblage, a part of the Yukon–Tanana composite terrane interpreted as trench mélange from a late Paleozoic – Mesozoic arc system, was the only tectonic assemblage known to include subducted material in the northern Cordillera. The discovery of eclogitic rocks in two parts of a klippe of the Anvil allochthonous assemblage, which comprises mafic ophiolitic rocks, above the Cassiar terrane west of the Tintina fault confirms other evidence that subducted oceanic crust was also returned to the surface. The eclogitic rocks have been largely retrograded by postsubduction metamorphism. Their existence is interpreted as additional evidence of the link between nappes above the Cassiar terrane and their inferred root, the Teslin suture zone. The Nisutlin and Anvil allochthonous assemblages can now be interpreted, not simply as crustally metamorphosed assemblages with minor, structurally interleaved high-pressure components, but as deeply metamorphosed and intensely strained slices of continental and oceanic crust switched from subducting slab to overriding plate and returned to the surface during collision of the arc with the North American margin.

Fracture-induced hydrothermal convection in the oceanic crust and the interpretation of heat-flow data

1996 ◽  
Vol 23 (9) ◽  
pp. 929-932 ◽  
Author(s):  
Jianwen Yang ◽  
R. N. Edwards ◽  
John W. Molson ◽  
E. A. Sudicky
Keyword(s):  
Heat Flow ◽  
Oceanic Crust ◽  
Flow Data ◽  
Hydrothermal Convection

Rapid cooling history of a Neotethyan ophiolite: Evidence for contemporaneous subduction initiation and metamorphic sole formation

2019 ◽  
Vol 131 (11-12) ◽  
pp. 2011-2038 ◽  
Author(s):  
Osman Parlak ◽  
István Dunkl ◽  
Fatih Karaoğlan ◽  
Timothy M. Kusky ◽  
Chao Zhang ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Carbonate Platform ◽  
Alkali Basalts ◽  
Tholeiitic Magma ◽  
Subduction Initiation ◽  
Suprasubduction Zone ◽  
Isparta Angle ◽  
History Of ◽  
Ophiolitic Rocks ◽  
Age Range

AbstractThe Beyşehir-Hoyran Nappes, including Mesozoic carbonate platform rocks, deep-sea sediments, and ophiolite-related units, crop out extensively on the western limb of the Isparta Angle in the Central Taurides, Turkey. The ophiolite-related rocks are represented by variably serpentinized harzburgitic mantle tectonites, tectonically underlain by a subophiolitic metamorphic sole and mélange. The harzburgitic mantle tectonites and metamorphic sole are intruded by undeformed isolated dikes. Protoliths of the metamorphic sole are similar to within-plate alkali basalts and associated sediments. The isolated dikes were geochemically derived mainly from tholeiitic magma and, to a lesser extent, from alkaline magma. Five isolated dike samples yielded U-Pb ages ranging from 90.8 ± 1.6 Ma to 87.6 ± 2.1 Ma (zircon) and from 102.3 ± 7.4 Ma to 87.5 ± 7.9 Ma (titanite). Seven amphibolite samples yielded U-Pb age ranges of 91.1 ± 2.1–88.85 ± 1.0 Ma (zircon) and 94.0 ± 4.8–90.0 ± 9.4 Ma (titanite) and a 40Ar-39Ar age range of 93.7 ± 0.3–91.4 ± 0.4 Ma (hornblende). U-Pb and 40Ar-39Ar ages of mineral phases with different closure temperatures (∼900–500 °C) from the isolated dikes and metamorphic sole rocks are almost identical and overlapping within 1σ, suggesting that both the magmatic growth of oceanic crust and formation of metamorphic sole were contemporaneous and cooled very rapidly. Hence, all the data should be interpreted as the crystallization ages of the ophiolite and metamorphic sole pair. Genesis of suprasubduction zone–type oceanic crust, genesis and exhumation of the metamorphic sole, and postmetamorphic dike emplacement within the Inner Tauride Ocean can be best explained by subduction initiation and rollback processes during the Late Cretaceous based on petrological and geochronological data obtained from the ophiolitic rocks of the Beyşehir-Hoyran Nappes.

scholarly journals Global atmospheric oxygen variations recorded by Th/U systematics of igneous rocks

2019 ◽  
Vol 116 (38) ◽  
pp. 18854-18859 ◽  
Author(s):  
He Liu ◽  
Robert E. Zartman ◽  
Trevor R. Ireland ◽  
Wei-dong Sun
Keyword(s):  
Oceanic Crust ◽  
Sea Water ◽  
Atmospheric Oxygen ◽  
Sharp Decrease ◽  
Temporal Variations ◽  
Global Scale ◽  
Significant Rise ◽  
Water Soluble ◽  
Igneous Rocks ◽  
Major Step

Atmospheric oxygen has evolved from negligible levels in the Archean to the current level of about 21% through 2 major step rises: The Great Oxidation Event (GOE) in the early Proterozoic and the Neoproterozoic Oxygenation Event (NOE) during the late Proterozoic. However, most previous methods for constraining the time of atmospheric oxygenation have relied on evidence from sedimentary rocks. Here, we investigate the temporal variations of the Th/U of arc igneous rocks since 3.0 billion y ago (Ga) and show that 2 major Th/U decreases are recorded at ca. 2.35 Ga and ca. 0.75 Ga, coincident with the beginning of the GOE and NOE. The decoupling of U from Th is predominantly caused by the significant rise of atmospheric oxygen. Under an increasingly oxidized atmosphere condition, more uranium in the surface environment became oxidized from the water-insoluble U4+ to the water-soluble U6+ valance and incorporated in the sea water and altered oceanic crust. Eventually, the subduction of this altered oceanic crust produced the low-Th/U signature of arc igneous rocks. Therefore, the sharp decrease of Th/U in global arc igneous rocks may provide strong evidence for the rise of atmospheric oxygen. We suggest that the secular Th/U evolution of arc igneous rocks could be an effective geochemical indicator recording the global-scale atmospheric oxygen variation.

Problems with imaging cellular hydrothermal convection in oceanic crust

1996 ◽  
Vol 23 (24) ◽  
pp. 3551-3554 ◽  
Author(s):  
Earl E. Davis ◽  
David S. Chapman
Keyword(s):  
Oceanic Crust ◽  
Hydrothermal Convection

An unequivocal case for high Nusselt number hydrothermal convection in sediment-buried igneous oceanic crust

1997 ◽  
Vol 146 (1-2) ◽  
pp. 137-150 ◽  
Author(s):  
Earl E. Davis ◽  
Kelin Wang ◽  
Jiangheng He ◽  
David S. Chapman ◽  
Heiner Villinger ◽  
...  
Keyword(s):  
Nusselt Number ◽  
Oceanic Crust ◽  
Hydrothermal Convection

scholarly journals Evolution of fluid flow and carbonate recrystallization rates in deep-sea sediments of the Equatorial Pacific

2022 ◽  
Vol 42 (1) ◽  
Author(s):  
Andreas Wittke ◽  
Nikolaus Gussone ◽  
Dominik Derigs ◽  
Barbara M. A. Teichert
Keyword(s):  
Fluid Flow ◽  
Oceanic Crust ◽  
Pore Water ◽  
Deep Sea ◽  
Convection Cell ◽  
Hydrothermal Convection ◽  
Deep Sea Sediments ◽  
Isotopic Equilibration ◽  
Sediment Cover ◽  
Pore Water Profile

AbstractFluid flow and carbonate recrystallization rates of deep-sea sediments from eight locations in the Equatorial Eastern Pacific were determined by using δ44/40Ca values of pore water and corresponding sediments. The studied drill sites of IODP Exp. 320/321 are located along a transect of decreasing crustal age and reveal different characteristic pore water depth profiles. The younger sites show an overall isotopic equilibration with the sediment in the upper part of the sedimentary column. In the lower part, the δ44/40Ca of the pore water increases back to seawater-like values at the sediment/basalt interface, forming a bulge-shaped pore water profile. The magnitude of the δ44/40Ca pore water bulge decreases with increasing age of the oceanic crust and sediment cover, resulting in seawater-like δ44/40Ca values throughout the sedimentary column in the oldest Sites U1331 and U1332. These findings indicate a seawater-like fluid input from the underlying crust into the sediment. Thus, after sedimentation, carbonate recrystallization processes start to enrich the pore water in 40Ca, and after a time of carbonate recrystallization and cooling of oceanic crust, a flow of seawater-like fluid starts to move upwards through the sedimentary column, enriching the pore water with 44Ca. We established a carbonate recrystallization and fluid flow model to quantify these processes. Our determined carbonate recrystallization rates between 0.000013e(−t/15.5) and 0.00038e(−t/100.5) and fluid flow rates in the range of 0.42–19 m*Myr−1 indicate that the fluid flow within the investigated sites of IODP Exp. 320/321 depends on the sedimentary composition and location of the specific site, especially the proximity to a recharge or discharge site of a hydrothermal convection cell.

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