Nd, Pb, and Sr isotope composition of Late Mesozoic to Quaternary intra-plate magmatism in NE-Africa (Sudan, Egypt): high-μ signatures from the mantle lithosphere

Abstract —We consider the isotope-geochemical features of epithermal fluorite deposits in Transbaikalia, including the REE compositions, Sr isotope ratios, Sm–Nd systems, and isotope compositions of oxygen, carbon, hydrogen, and sulfur. The 87Sr/86Sr ratios in fluorites are within 0.706–0.708, and the εNd values are negative. Oxygen in quartz, the main mineral of the deposits, has a light isotope composition (δ18O = –3.4 to +2.6‰), and the calculated isotope composition of oxygen in the fluid in equilibrium with quartz (δ18O = –9 to –16‰) indicates the presence of meteoric water. The latter is confirmed by analysis of the isotope compositions of oxygen and hydrogen in gas–liquid inclusions in fluorites from three deposits. These isotope compositions are due to recycling caused by the impact of shallow basic plutons. The isotope composition of sulfur indicates its deep source. During ascent, sulfur became enriched in its light isotope (δ34S = –1.8 to –7.7‰). We assess the association of fluorite ores with basaltoids widespread in the study area. The isotope and geochemical parameters suggest their spatial proximity. Probably, the basaltoids were responsible for the recycling of meteoric water. It is shown that the epithermal fluorite deposits formed by the same mechanism as fissure–vein thermal waters in western Transbaikalia.

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Oxygen–carbon isotope composition of Middle Jurassic–Cretaceous molluscs from the Saratov–Samara Volga region and main climate trends in the Russian Platform–Caucasus

Geological Society London Special Publications ◽

10.1144/sp498-2018-57 ◽

2019 ◽

Vol 498 (1) ◽

pp. 101-127 ◽

Cited By ~ 1

Author(s):

Yuri D. Zakharov ◽

Vladimir B. Seltser ◽

Mikheil V. Kakabadze ◽

Olga P. Smyshlyaeva ◽

Peter P. Safronov

Keyword(s):

Carbon Isotope ◽

Middle Jurassic ◽

Isotope Composition ◽

Russian Platform ◽

Volga Region ◽

Published Data ◽

Climate Trends ◽

Late Mesozoic ◽

Oxygen And Carbon Isotope ◽

Epipelagic Zone

AbstractOxygen and carbon isotope data from well-preserved mollusc shells and belemnite rostra are presented from the Jurassic (Bathonian, Callovian and Tithonian) and Cretaceous (Aptian, Turonian, Campanian and Maastrichtian) of the Saratov–Samara Volga region, Russia. New data provide information on the resulting trends in palaeoclimate and in palaeoceanography and palaeoecology in the late Mesozoic. Palaeotemperatures calculated from Jurassic–Cretaceous benthic (bivalves and gastropods) and semi-pelagic (ammonites) molluscs are markedly higher than those calculated from pelagic belemnites using oxygen isotopes. This is probably due to various mollusc groups of the Saratov–Samara area inhabiting different depths in the marine basins (e.g. epipelagic v. mesopelagic). Our isotope records, combined with a review of previously published data from shallow-water fossils from the Saratov–Samara area and adjacent regions permits us to infer temperature trends for the epipelagic zone from the Middle Jurassic to Cretaceous in the Russian Platform–Caucasus area. The Jurassic–Cretaceous belemnites from the Russian Platform and the Caucasus have a lower δ13C signature than the contemporaneous brachiopods, bivalves and ammonites.

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Lower Permian brachiopods from Oman: their potential as climatic proxies

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s1755691008075634 ◽

2007 ◽

Vol 98 (3-4) ◽

pp. 327-344 ◽

Cited By ~ 6

Author(s):

L. Angiolini ◽

D. P. F. Darbyshire ◽

M. H. Stephenson ◽

M. J. Leng ◽

T. S. Brewer ◽

...

Keyword(s):

Isotope Composition ◽

Isotopic Analysis ◽

Lower Permian ◽

Published Data ◽

Sr Isotope ◽

Marine Sedimentation ◽

Ice Accumulation ◽

Secondary Layer ◽

Data Points ◽

Few Data

ABSTRACTThe Lower Permian of the Haushi basin, Interior Oman (Al Khlata Formation to Saiwan Formation/lower Gharif member) records climate change from glaciation, through marine sedimentation in the Haushi sea, to subtropical desert. To investigate the palaeoclimatic evolution of the Haushi Sea we used O, C, and Sr isotopes from 31 brachiopod shells of eight species collected bed by bed within the type-section of the Saiwan Formation. We assessed diagenesis by scanning electron microscopy of ultrastructure, cathodoluminescence, and geochemistry, and rejected fifteen shells not meeting specific preservation criteria. Spiriferids and spiriferinids show better preservation of the fibrous secondary layer than do orthotetids and productids and are therefore more suitable for isotopic analysis. δ18O of −3·7 to −3·1℅ from brachiopods at the base of the Saiwan Formation are probably related to glacial meltwater. Above this, an increase in δ18O may indicate ice accumulation elsewhere in Gondwana or more probably that the Haushi sea was an evaporating embayment of the Neotethys Ocean. δ13C varies little and is within the range of published data: its trend towards heavier values is consistent with increasing aridity and oligotrophy. Saiwan Sr isotope signatures are less radiogenic than those of the Sakmarian LOWESS seawater curve, which is based on extrapolation between few data points. In the scenario of evaporation in a restricted Haushi basin, the variation in Sr isotope composition may reflect a fluvial component.

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Isotopic Compositions of Selected Ore Leads from Northeastern Washington

Canadian Journal of Earth Sciences ◽

10.1139/e73-067 ◽

1973 ◽

Vol 10 (5) ◽

pp. 670-678 ◽

Cited By ~ 5

Author(s):

W. D. Small

Keyword(s):

Isotopic Composition ◽

Lead Isotope ◽

Isotope Composition ◽

Canadian Cordillera ◽

Basement Structure ◽

Late Mesozoic ◽

Sedimentary Structures ◽

Lead Isotope Composition ◽

Isotopic Abundances ◽

Primary Type

Isotopic composition of ore leads from four districts in northeastern Washington has been measured with a precision in the ratios of about 0.1‰. Results indicate that the mineralization in the Marshall Diorites of Pend Oreille County is by a primary type lead with a model age of about 1300 to 1500 m.y. The remainder of the measured leads from Pend Oreille and Stevens Counties have a radiogenic component which could have developed in a closed system during the interval 1370 to about 250 m.y. ago. Leads from Ferry and Okanogan Counties have only slight variations in their isotopic abundances. These latter leads could have been produced by an homogenization of the leads from Pend Oreille and Stevens Counties through the mechanism of a late Mesozoic metamorphism of Mesozoic sedimentary structures in Ferry and Okanogan Counties, these latter sedimentary structures being the products of erosion of rocks in Pend Oreille and Stevens Counties. There is no evidence of an ancient basement structure under Ferry and Okanogan Counties from the data presented herein. The lead isotope composition of the ores from northeastern Washington is compatible with the current concepts of the crustal structure across the Canadian Cordillera.

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