Collisional and alteration history of the CM parent body

Abstract

Boriskino is a little studied CM2 chondrite composed of millimeter-sized clasts of different lithologies and degrees of alteration. Boriskino thus offers a good opportunity to better understand the preaccretionary alteration history and collisional evolution that took place on the CM parent body. The least altered lithology displays 16 O-poor Type 1a calcite and aragonite grains ( 18 O ≈ 30-37‰,  17 O ≈ 15-18‰ and  17 O ≈-2 to 0‰, SMOW) that precipitated early, before the establishment of the petrofabric, from a fluid whose isotopic composition was established by isotopic exchange between a 16 O-poor water and 16 O-rich anhydrous silicates. In contrast, the more altered lithologies exhibit 16 O-rich Type 2a and veins of calcite ( 18 O ≈ 17-23‰,  17 O ≈ 6-9‰ and  17 O ≈-4 to-1‰, SMOW) that precipitated after establishment of the deformation, from transported 16 O-rich fluid in preexisting fractures. From our petrographic and X-ray tomographic results, we propose that the more altered lithologies of Boriskino were subjected to high intensity impact(s) (10-30 GPa) that produced a petrofabric, fractures and chondrule flattening. Taking all our results together, we propose a scenario for the deformation and alteration history of Boriskino, in which the petrographic and isotopic differences between the lithologies are explained by their separate locations into a single CM parent body. Based on the  13 C- 18 O values of the Boriskino Type 2a calcite ( 13 C ≈ 30-71‰, PDB), we propose an alternative  13 C- 18 O model where the precipitation of Type 2a calcite can occurred in an open system environment with the escape of 13 C-depleted CH 4 produced from the reduction of C-bearing species by H 2 released during serpentinization or kamacite corrosion. Assuming a mean precipitation temperature of 110°C, the observed δ 13 C variability in T2a calcite can be reproduced by the escape of ≈ 15-50% of dissolved carbon into CH 4 by Rayleigh distillation.

Testing the genetic relationship between fluid alteration and brecciation in CM chondrites

“…We compiled our measurements of the O‐isotopic compositions of carbonates in the section 3788‐1 of Boriskino with those already reported for sections 3788‐3 and ‐4 from Vacher et al. (). The lithology 1 reported in their study corresponds to our lithology A, while others exhibit textures and abundances of major constituents that differ from the ones in our study.…”

“…), we assumed that they precipitated from the same water as the cc5‐1 carbonate in section 3788‐3 (Vacher et al. ), which precipitated at 71 °C (Table ). Considering ∆ sw = 8‰ at 70 °C, this yields .…”

“…; Vacher et al. ). CM chondrites thus recorded the postaccretion evolution of asteroids and enabled regolith gardening to be studied in detail.…”

THE CONCISE GUIDE TO PHARMACOLOGY 2017/18: G protein‐coupled receptors

“…Knock-out of the GABA B1 subunit in C57B mice causes the development of severe tonic-clonic convulsions that prove fatal within a month of birth, whereas GABA B1 -/-BALB/c mice, although also displaying spontaneous epileptiform activity, are viable. The phenotype of the latter animals additionally includes hyperalgesia, hyperlocomotion (in a novel, but not familiar, environment), hyperdopaminergia, memory impairment and behaviours indicative of anxiety [510,2008]. A similar phenotype has been found for GABA B2 -/-BALB/c mice [613].…”

“…Boatman PD et al (2008) The human BLT 1 receptor is the high affinity LTB 4 receptor whereas the BLT 2 receptor in addition to being a low-affinity LTB 4 receptor also binds several other lipoxygenase-products, such as 12S-HETE, 12S-HPETE, 15S-HETE, and the thromboxane synthase product 12-hydroxyheptadecatrienoic acid. The BLT receptors mediate chemotaxis and immunomodulation in several leukocyte populations and are in addition expressed on non-myeloid cells, such as vascular smooth muscle and endothelial cells.…”