Interstellar Gas and X-rays toward the Young Supernova Remnant RCW 86; Pursuit of the Origin of the Thermal and Non-Thermal X-ray

We have analyzed the atomic and molecular gas using the 21 cm HI and 2.6/1.3 mm CO emissions toward the young supernova remnant (SNR) RCW 86 in order to identify the interstellar medium with which the shock waves of the SNR interact. We have found an HI intensity depression in the velocity range between $-46$ and $-28$ km s$^{-1}$ toward the SNR, suggesting a cavity in the interstellar medium. The HI cavity coincides with the thermal and non-thermal emitting X-ray shell. The thermal X-rays are coincident with the edge of the HI distribution, which indicates a strong density gradient, while the non-thermal X-rays are found toward the less dense, inner part of the HI cavity. The most significant non-thermal X-rays are seen toward the southwestern part of the shell where the HI gas traces the dense and cold component. We also identified CO clouds which are likely interacting with the SNR shock waves in the same velocity range as the HI, although the CO clouds are distributed only in a limited part of the SNR shell. The most massive cloud is located in the southeastern part of the shell, showing detailed correspondence with the thermal X-rays. These CO clouds show an enhanced CO $J$ = 2-1/1-0 intensity ratio, suggesting heating/compression by the shock front. We interpret that the shock-cloud interaction enhances non-thermal X-rays in the southwest and the thermal X-rays are emitted by the shock-heated gas of density 10-100 cm$^{-3}$. Moreover, we can clearly see an HI envelope around the CO cloud, suggesting that the progenitor had a weaker wind than the massive progenitor of the core-collapse SNR RX J1713.7$-$3949. It seems likely that the progenitor of RCW 86 was a system consisting of a white dwarf and a low-mass star with low-velocity accretion winds.Comment: 19 pages, 15 figures, 4 tables, accepted for publication in Journal of High Energy Astrophysics (JHEAp

Origin of the Paleoproterozoic “Giant Quartz Reef” System in the Bundelkhand Craton, India: Constraints from Fluid Inclusion Microthermometry, Raman Spectroscopy, and Geochemical Modelling

AbstractThe Bundelkhand “giant quartz reef” (BGQR) system comprises 20 major quartz reefs which run for tens of km in strike length of average width of 40 m and occurs in spatial intervals of 12–19 km in the Bundelkhand craton, North Central India. The BGQR system is distinct from quartz vein systems originating from crustal scale shearing observed in ancient as well as modern convergent tectonic settings. Fluid inclusions studied in BGQR system are intriguingly diverse although dominated by aqueous fluid which exhibit a broad range of salinity from ~0 to 28.9 wt% NaCl equivalent and temperature of homogenization range of 58 to 385°C. Primary and pseudosecondary aqueous inclusions in assemblages in grain interiors and growth zones vary randomly in their Th—salinity characteristics that preclude identification of discrete fluid events. Aqueous fluid in the BGQR system evolved through mixing of two distinct sources of fluids—a meteoric fluid and a moderate temperature—moderate salinity fluid that was possibly derived from the Bundelkhand granodiorite based on an important clue provided by hydrous mineral bearing fluid inclusions detected by Raman microspectrometry. The results of modeling with PHREEQC indicate that mixing of fluids could be a suitable mechanism in formation of these giant reefs. The available 1-dimensional diffusive transport model for deposition of silica helps in putting constraints on the time span of deposition of silica in the context of the BGQR system. The BGQR system is a possible result of shallow-crustal sources of fluid and silica and could be visualized as a “Paleoproterozoic geothermal system” in a granitic terrane

Mineral thermobarometry and fluid inclusion studies on the Closepet granite, Eastern Dharwar Craton, south India: implications to emplacement and evolution of late-stage fluid

The Closepet granite (CPG), a spectacularly exposed magmatic body along with other intrusive bodies (to the east of it) typifies the late Archean granitic activity in the Eastern Dharwar Craton (EDC), south India. In the present study, the P-T-fO₂ conditions of emplacement and physico-chemical environment of the associated magmatic-hydrothermal regime of CPG have been retrieved on the basis of mineral chemical and fluid inclusion studies. Amphibole-plagioclase Ti-in-amphibole and Ti-in-biotite geothermometers along with Al-in-amphibole geobarometer have been used to reconstruct the emplacement temperature and pressure conditions in the majority of the pluton. Estimated temperatures of emplacement of CPG vary from to 740 to 540 °C. A variation of pressure from 4.8 to 4.1 kilo bars corresponding to this temperature range was obtained. While there is a faint south to north negative gradient in temperature, the variation of pressure does not seem to follow this trend and indicates more or less same crustal level of emplacement for the body between Ramanagaram–Kalyandurga segment extending for about 230 km. Mineral chemistry of biotite indicates crystallization of CPG under high oxygen fugacity conditions (mostly above QFM buffer) with no clear spatial variation in the fugacity of halogen species in the late-stage magmatic fluid. It may be surmised that barring the southernmost part of CPG, there is no perceptible variation in the physicochemical environment of emplacement. Fluid Inclusion studies in the granitic matrix quartz and pegmatite/vein quartz show dominance of H₂O and H₂O–CO₂ fluids respectively in them. The difference in the fluid characteristics is interpreted in terms of the initial loss of CO₂ rich fluid from granitic magma and aqueous-rich nature during the later stages of crystallization of quartz. The exsolved CO₂-rich fluid was responsible in formation of the later quartz and pegmatitic veins at different crustal levels and also possibly was responsible in CO₂ – induced metamorphism (charnockitization) preserved in the Kabbaldurga area in the southernmost part. The fluid characteristics in the vast tract of CPG revealed from mineral chemical and fluid inclusion studies make a case for its involvement in gold mineralization in the schist belts in EDC

Relative abundances of foraminifera and age models of DSDP Site 22-214 (eastern Indian Ocean) and ODP Hole 130-807A (western Pacific)

This study investigates the timing of development of oligotrophic conditions and thickening of the West Pacific Warm Pool (WPWP) during the Pliocene. It has been hypothesized that the evolution of the WPWP and the establishment of strong equatorial Pacific zonal gradients are closely related to the narrowing of the Indonesian Gateway (IG) as well as the closure of the Central American Seaway (CAS). However, the timing of these events remains unclear. Here we report Pliocene-to-recent relative abundances of planktic foraminifera at DSDP Site 214, in the eastern Indian Ocean, and at ODP Site 807, in the western Pacific, along with stable isotope values at the latter site. A comparison of the abundance of mixed-layer species (MLS) from both sites indicates a pronounced increase in their population between ~3.15 and 1.6 Ma. On the contrary, there is a contemporaneous decrease in the Globigerinita glutinata population during this time, which together suggest the development of oligotrophic conditions in the western tropical Pacific. Our data suggest that the oligotrophic WPWP resembling present-day conditions developed around ~3.15 Ma, and was closely linked to the gradual constriction of the IG

A 23000 year old record of paleoclimatic and environmental changes from the eastern Arabian Sea

Climate of the eastern Arabian Sea is highly influenced by both global climate and Indian monsoon. We produced multi-proxy records of benthic foraminiferal biofacies and stable isotope ratio (δC and δO), planktic foraminifera and total organic carbon (wt%) content of sediments from core SK291/GC11 in the upper continental shelf off Mangalore, off eastern Arabian Sea (EAS) to decipher paleoenvironmental and paleoclimatic changes during the past ~23,000 years. The monsoon was weak during the Last Glacial Maximum ~23,000–18,000 calibrated years before Present (cal yr BP) when sea level was lower. Globigerinoides ruber populations fluctuate from 30 to 60% in the studied interval with a maximum during ~6000–5000 cal yr BP and a minimum during 19,000–17,000 cal yr BP. The δO values of benthic foraminifer Ammonia gaimardii suggest pronounced cooling phases during ~23,000–18,000 cal yr BP, and a short-term cooling at ~6000 cal yr BP. Several intervals of high organic productivity and low oxygen conditions were identified based on benthic foraminiferal biofacies during 23,247–682 cal yr BP. Wind-induced surface mixing was intense during 3200–530 cal yr BP as evidenced by high Globigerina bulloides abundances. The core was affected by moderate chemical weathering and solar variability appears to have been an important forcing factor in shaping climate of the region