Mesoproterozoic emplacement and enriched mantle derivation of the Racherla alkali syenite, Palaeo-Mesoproterozoic Cuddapah Basin, southern India: insights from in situ Sr–Nd isotopic analysis on apatite

Comets are primitive, kilometer-sized bodies that formed in the outer regions of the solar system. Composed of ice and dust, comets are generally believed to be relic building blocks of the outer solar system that have been preserved at cryogenic temperatures since the formation of the Sun and planets. The analysis of cometary material is particularly important because the properties of cometary material provide direct information on the processes and environments that formed and influenced solid matter both in the early solar system and in the interstellar environments that preceded it.The first direct analyses of proven comet dust were made during the Soviet and European spacecraft encounters with Comet Halley in 1986. These missions carried time-of-flight mass spectrometers that measured mass spectra of individual micron and smaller particles. The Halley measurements were semi-quantitative but they showed that comet dust is a complex fine-grained mixture of silicates and organic material. A full understanding of comet dust will require detailed morphological, mineralogical, elemental and isotopic analysis at the finest possible scale. Electron microscopy and related microbeam techniques will play key roles in the analysis. The present and future of electron microscopy of comet samples involves laboratory study of micrometeorites collected in the stratosphere, in-situ SEM analysis of particles collected at a comet and laboratory study of samples collected from a comet and returned to the Earth for detailed study.

Download Full-text

In situ isotopic analysis of uranium using a new data acquisition protocol for 1013 ohm Faraday amplifiers

Journal of Analytical Atomic Spectrometry ◽

10.1039/d0ja00498g ◽

2021 ◽

Author(s):

Kota Yamamoto ◽

Hisashi Asanuma ◽

Hiroaki Takahashi ◽

Takafumi Hirata

Keyword(s):

Data Acquisition ◽

Data Reduction ◽

Reduction Method ◽

Isotopic Analysis ◽

High Gain ◽

Transient Signals ◽

Acquisition Protocol ◽

Data Reduction Method ◽

Isotopic Measurements

New data reduction method for isotopic measurements using high-gain Faraday amplifiers enables precise uranium isotopic analysis even from transient signals.

Download Full-text

Constraining the tectonic setting of continental crust formation from coupled in situ Rb-Sr dating and Pb isotopic analysis of detrital, single K-feldspar grains

10.7185/gold2021.5245 ◽

2021 ◽

Author(s):

Dan Bevan ◽

Christopher Coath ◽

Jamie Lewis ◽

Daniel Stubbs ◽

Joel Rodney ◽

...

Keyword(s):

Continental Crust ◽

Tectonic Setting ◽

Isotopic Analysis ◽

Crust Formation

Download Full-text

Metamorphic chronology of the Precambrian provinces of South India

Canadian Journal of Earth Sciences ◽

10.1139/e68-054 ◽

1968 ◽

Vol 5 (3) ◽

pp. 591-600 ◽

Cited By ~ 14

Author(s):

U. Aswathanarayana

Keyword(s):

South India ◽

Regional Metamorphism ◽

Southern India ◽

Eastern Ghats ◽

Cuddapah Basin ◽

Upper Limit

There are three Precambrian provinces in southern India — the Dharwars (metavolcanics, metasediments, charnockites and granites), the Eastern Ghats (metasediments, charnockites and granites), and the Cuddapahs (essentially flat-lying continental sediments disturbed at the margins) — with chronostratigraphic histories dovetailing into one another. The Dharwars bear the impress of three episodes (about 3000 m.y., 2600–2300 m.y., and about 2000 m.y.) of folding, metamorphism, and emplacement of granites, the second being the most important. The pelitic sediments deposited in the Eastern Ghats geosyncline during the post-Dharwar times (upper limit, 2600 m.y.) were later folded and metamorphosed about 1600 m.y. ago into garnet-sillimanite-graphite gneisses (khondalites). Important deposits of mica pegmatites developed during this episode. Charnockites and granites associated with the Eastern Ghats were emplaced 1520–1300 m.y. ago. The Eastern Ghats rocks were subsequently cross-folded and metamorphosed about 500 m.y. ago. The sedimentation in the Cuddapah Basin was initiated sometime after the Eastern Ghats orogeny (1600 m.y. ago) but before 1160 m.y. ago. The Cuddapahs were subjected to regional metamorphism about 500 m.y. ago.

Download Full-text