Chemical and oxygen isotopic properties of ordinary chondrites (H5, L6) from Oman: Signs of isotopic equilibrium during thermal metamorphism

2017 ◽  
Vol 52 (10) ◽  
pp. 2097-2112 ◽  
Author(s):  
Arshad Ali ◽  
Sobhi J. Nasir ◽  
Iffat Jabeen ◽  
Ahmed Al Rawas ◽  
Neil R. Banerjee ◽  
...  
Keyword(s):  
Ordinary Chondrites ◽  
Isotopic Equilibrium ◽  
Thermal Metamorphism ◽  
Oxygen Isotopic

Thermal Metamorphism of Primitive Meteorites—XII. The Enstatite Chondrites Revisited

2005 ◽  
Vol 2 (3) ◽  
pp. 215 ◽  
Author(s):  
Ming-Sheng Wang ◽  
Michael E. Lipschutz
Keyword(s):  
Radiochemical Neutron Activation Analysis ◽  
Parent Material ◽  
Ordinary Chondrites ◽  
Terrestrial Environment ◽  
Volatile Element ◽  
Thermal Metamorphism ◽  
Report Data ◽  
Element Contents ◽  
Type 3 ◽  
Solid Bodies

Environmental Context.The first Solar System material condensed 4.567 billion years ago, rapidly forming planetesimals—solid bodies that might combine to form planets (accretion) or survive as asteroidal meteorites. Earth’s main accretion ended within the next 30 million years, but subsequent high temperatures essentially erased evidence of this history. However, heating in these early episodes produced effects uniquely recorded by 14 volatile trace elements. The volatile element composition of chondritic meteorites, whose parent material formed closest to Earth, may thus provide important information about early planetesimal evolution. Abstract.We report data for 14 trace and ultratrace elements—Au, Co, Sb, Ga, Rb, Ag, Cs, Te, Zn, Cd, Bi, Tl, In (ordered by increasing putative nebular volatility)—in 13 enstatite (E) chondrites recovered from Antarctica and two E inclusions in the Kaidun polymict breccia that fell in 1980. These data, determined by radiochemical neutron activation analysis (RNAA), essentially double the amount of information known for E chondrites, whose parent materials formed closest to the Sun in the chondrite-forming nebular region. We discuss here the data for all 29 samples studied. The meteoritic suite studied here includes both representatives of previously rare types—like high-iron EH3 and EH5 individuals—but also unique individuals and previously unknown low-iron, EL3, chondrites. Prior hypothetical assertions by others are corrected by the new data. Volatile element contents of EL3 and EH3 chondrites are variable, but comparable, like those of type 3 ordinary chondrites (i.e. H3, L3, and LL3). Volatile element contents of EH4 chondrites are at least as high as those of the E3 types, in contrast to the lower contents of H4, L4, and LL4 types. Compositionally, E3,4 chondrites reflect only nebular condensation and/or accretion processes. Volatiles in E5 and E6 chondrites—whether of EH, EL or unique ones—are depleted relative to cosmic (i.e. CI1) or E3,4 chondrite abundances. The evidence indicates that E5,6 chondrites compositionally reflect vaporization and loss of volatiles during open-system, thermal metamorphism of their parent(s); this may have been the terrestrial environment during Earth’s formation from early planetesimals. Compositional differences between Antarctic E5,6 chondrites and contemporary falls probably do not reflect weathering during the long residence of these chondrites in Antarctica. They might reflect differences in the starting compositions and/or metamorphic conditions in the parent(s).

scholarly journals Potential of Stable Carbon and Oxygen Isotope Variations of Speleothems from Andaman Islands, India, for Paleomonsoon Reconstruction

2011 ◽  
Vol 2011 ◽  
pp. 1-7 ◽  
Author(s):  
Amzad H. Laskar ◽  
S. Raghav ◽  
M. G. Yadava ◽  
R. A. Jani ◽  
A. C. Narayana ◽  
...  
Keyword(s):  
Monsoon Rainfall ◽  
Boreal Summer ◽  
Stable Carbon ◽  
The South ◽  
Isotopic Equilibrium ◽  
The Past ◽  
Carbon And Oxygen Isotope ◽  
Show Evidence ◽  
Oxygen Isotopic ◽  
India Receive

The Indian monsoon activity, coinciding with the Inter-Tropical Convective Zone (ITCZ), progresses from the southern Indian Ocean during the boreal summer and withdraws towards the south in winter. Islands situated to the south of India receive, therefore, the first and last showers of the monsoon; speleothems in such islands have not yet been explored for their potential to reconstruct past monsoon rainfall. Here, we present the first measurements of stable carbon and oxygen isotopic compositions (δ13C and δ18O) of a stalagmite collected from the Baratang Island of Andamans, along with new data on δ18O of modern monsoon precipitation (May to July 2010). The aim was to detect (i) whether these samples are amenable to dating using 14C, (ii) whether their oxygen isotopes indicate precipitation under isotopic equilibrium, and (iii) if (i) and (ii) above are true, can we reconstruct monsoon activity during the past few millennia? Our results indicate that while δ18O of speleothem does show evidence for precipitation under isotopic equilibrium; dating by 14C shows inversions due to varying contributions from dead carbon. The present work highlights the problems and prospects of speleothem paleomonsoon research in these islands.

Isotopic variations in primitive meteorites

1981 ◽  
Vol 303 (1477) ◽  
pp. 339-349 ◽  
Keyword(s):  
Solar System ◽  
Time Scale ◽  
Decay Product ◽  
Common Source ◽  
Time Interval ◽  
Crystal Formation ◽  
Ordinary Chondrites ◽  
Gas Reservoir ◽  
Oxygen Isotopic ◽  
Isotopic Variations

Oxygen isotopic variations in carbonaceous chondrites and in ordinary chondrites can each be interpreted as mixtures of two isotopically different reservoirs, one consisting of solids, enriched in 16 O , the other of a gas, depleted in 16 O relative to terrestrial abundances. The data suggest a common source of the solids for each of the two classes of meteorites, but a different gas reservoir for each. These conditions might prevail in gaseous protoplanets. Radiogenic 26 Mg is variable in abundance among some classes of Allende inclusions, implying either nebular heterogeneity with respect to 26 A1/ 27 Al ratios, or time differences of crystal formation of 1 or 2 x 10 6 a. The presence of excess 107 Ag from decay of extinct 107 Pd supports the evidence from 26 Mg for a time interval of at most a few million years between the last nucleosynthetic event and accretion of substantial bodies in the Solar System. The widespread small excess of 50 Ti in Allende inclusions is tantalizing, but unexplained. An exceptional hibonite-rich inclusion from Allende contains strongly fractionated isotopes of oxygen and calcium, but isotopically normal magnesium. Its trace elements imply association with a hot, oxidized gas. Among the volatile elements, neon-E has been shown to be essentially pure 22 Ne, and appears to be the decay product of extinct 22 Na. If so, condensation of some stellar ejecta must take place on a time scale of a year or so. The problem of reconciling the 26 A1 time scale of about 10 6 years between nucleosynthesis and Solar System condensation with the 10 8 year scale implied by the decay of 129 I to 129 Xe and fission of 244 Pu requires that at most a small fraction of the 129 I and 244 Pu be formed in the most recent event. Progress has been made in establishing the carrier phases of isotopically anomalous xenon and krypton. The apparent location of anomalous xenon and 14 N-rich nitrogen in identical carriers supports the notion that nucleosynthetic anomalies in nitrogen are also present in Allende.

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