scholarly journals Paleoproterozoic age of carbonates and trondhjemites of the central azov group: Sr-isotope chemostratigraphy and U-Pb geochronology

2019 ◽  
Vol 484 (6) ◽  
pp. 725-728
Author(s):  
A. B. Kuznetsov ◽  
S. B. Lobach-Zhuchenko ◽  
T. V. Kaulina ◽  
G. V. Konstantinova
Keyword(s):  
Isotope Composition ◽  
Sedimentary Cover ◽  
Sr Isotope ◽  
Early Precambrian ◽  
Nd Model Age

The Sr-isotope composition of the Central Azov Group carbonates (0.70322-0.70352) and Nd model age of silicate sediments (2.34-2.31 Ga) has been reported. The U-Pb age of trondhjemite (2052+5 Ma) cutting the carbonates has been determined. According to the obtained data, the marine sedimentary cover of the Azov block making up the Early Precambrian Sarmatia Continent emplaced in the Early Paleoproterozoic at 2.23-2.34 Ga.

Nd, Pb, and Sr isotope composition of juvenile magmatism in the Mesozoic large magmatic province of northern Chile (18–27°S): indications for a uniform subarc mantle

2006 ◽  
Vol 152 (5) ◽  
pp. 571-589 ◽  
Author(s):  
Friedrich Lucassen ◽  
Wolfgang Kramer ◽  
Viola Bartsch ◽  
Hans-Gerhard Wilke ◽  
Gerhard Franz ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Northern Chile ◽  
Sr Isotope

Epithermal Fluorite Deposits in Transbaikalia (Geochemical Features, Sources of Matter and Fluids, and Genesis)

2021 ◽  
Vol 62 (4) ◽  
pp. 415-426
Author(s):  
E.I. Lastochkin ◽  
G.S. Ripp ◽  
D.S. Tsydenova ◽  
V.F. Posokhov ◽  
A.E. Murzintseva
Keyword(s):  
Meteoric Water ◽  
Isotope Composition ◽  
Spatial Proximity ◽  
Thermal Waters ◽  
Sr Isotope ◽  
Light Isotope ◽  
Geochemical Parameters ◽  
Nd Systems ◽  
Deep Source ◽  
The Impact

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.

Sr Isotope Chemostratigraphy and Pb–Pb Age of the Riphean Carbonate Deposits of the Kharaulakh Uplift (Northeastern Margin of the Siberian Platform)

2021 ◽  
Vol 62 (03) ◽  
pp. 377-387
Author(s):  
B.B. Kochnev ◽  
A.B. Kuznetsov ◽  
D.R. Sitkina ◽  
A.Yu. Kramchaninov
Keyword(s):  
Siberian Platform ◽  
Sedimentary Cover ◽  
Complex Structure ◽  
The Arctic ◽  
86Sr Ratio ◽  
Sr Isotope ◽  
Upper Riphean ◽  
Carbonate Deposits

Abstract —The least altered limestones of the Ukta and Eselekh formations in the Precambrian section of the Kharaulakh uplift have a minimum 87Sr/86Sr ratio of 0.70673–0.70715. The lowest 87Sr/86Sr ratio of the overlying Neleger and Sietachan formations is 0.70791–0.70817. Based on these data, along with the earlier obtained positive δ13С values (up to 8‰) for the Kharaulakh section, we have estimated the age of the Ukta and Eselekh formations at 800–670 Ma and the age of the Neleger and Sietachan formations at ~640–580 Ma. The Pb–Pb isochron age of the least altered limestones of the Eselekh Formation calculated from eight samples is 720 ± 30 Ma. This age permits us to define the lower part of the Kharaulakh section of the Ukta and Eselekh formations to be the late Tonian of the International Chronostratigraphic Chart or to the Upper Riphean of the General Stratigraphic Scale of Russia. The presence of reliably dated Upper Riphean sediments in the Kharaulakh uplift indicates a more complex structure of the Precambrian sedimentary cover on the Arctic margin of the Siberian Platform than assumed earlier.

scholarly journals Lower Permian brachiopods from Oman: their potential as climatic proxies

2007 ◽  
Vol 98 (3-4) ◽  
pp. 327-344 ◽  
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.

Sr isotope composition of sea water over the past 75 Myr

Nature ◽  
1985 ◽  
Vol 314 (6011) ◽  
pp. 526-528 ◽  
Author(s):  
M. R. Palmer ◽  
H. Elderfield
Keyword(s):  
Sea Water ◽  
Isotope Composition ◽  
Sr Isotope ◽  
The Past

Nd and Sr Isotope Composition in the Tooth Enamel from Fe–Mn Nodules of the Cape Basin (Atlantic Ocean): Age and Sources

2018 ◽  
Vol 56 (12) ◽  
pp. 1209-1219 ◽  
Author(s):  
A. V. Dubinin ◽  
A. B. Kuznetsov ◽  
M. N. Rimskaya-Korsakova ◽  
T. Kh. Safin
Keyword(s):  
Atlantic Ocean ◽  
Tooth Enamel ◽  
Isotope Composition ◽  
Sr Isotope ◽  
Cape Basin

Sr isotope fractionation in a karst river: case study of Krka, Croatia

2021 ◽  
Author(s):  
Sonja Lojen ◽  
Qasim Jamil ◽  
Tea Zuliani ◽  
Leja Rovan ◽  
Tjaša Kanduč ◽  
...  
Keyword(s):  
Trace Element ◽  
Isotope Fractionation ◽  
Solid Phase ◽  
Isotope Composition ◽  
Karst Water ◽  
Carbonate Precipitation ◽  
Sr Isotopes ◽  
Sr Isotope ◽  
Element Partitioning ◽  
Karst River

<p>Precipitation of calcite from water fractionates strontium (Sr) isotopes because of preferential incorporation of light (<sup>86</sup>Sr) isotopes into the solid phase, making continental carbonates one of the most <sup>88</sup>Sr depleted reservoirs. It was suggested that carbonate precipitation is the most likely process controlling <em>δ</em><sup>88/86</sup>Sr composition of karst water. Therefore, the <sup>88</sup>Sr enrichment of river water could be used for the estimation of Sr and carbonate precipitation at catchment scale.</p><p>In the present study, we report on trace element partitioning and Sr isotope fractionation between tufa and water in the groundwater fed karst river Krka (Croatia). Water and tufa along with samples of bedrock and soil as the main contributors of dissolved and particulate Sr at seven main waterfalls and cascades along a 33 km section of the river were analysed for trace element and Sr isotope composition (<em>δ</em><sup>88/86</sup>Sr).</p><p>The highest δ<sup>88/86</sup>Sr values were measured in soils and in siliciclastic rocks, while in limestone, the <em>δ</em><sup>88/86</sup>Sr values were similar to those of old tufa precipitated in the period between 96 and 141 ky BP. Recent tufa, however, was considerably depleted in <sup>88</sup>Sr. The isotope fractionation between water and recent tufa varied a lot and was inversely correlated with Mg and Sr partitioning coefficients, while correlations with precipitation rates and temperature were rather weak. The <em>δ</em><sup>88/86</sup>Sr of recent tufa was strongly correlated with the stable isotope composition of organic carbon, which indicates that apart from hydrochemical, hydraulic parameters and temperature, plants and microbial communities that knowingly stimulate the tufa formation also affect the isotope fractionation of Sr.</p>

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