Clasts in theCM2 carbonaceous chondrite Lonewolf Nunataks 94101: Evidence for aqueous alteration prior to complex mixing

Abstract

Abstract-Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks (LON) 94101 have been characterized using scanning and transmission electron microscopy and electron microprobe analysis to determine their degrees of aqueous alteration, and the timing of alteration relative to incorporation of clasts into the host. The provenance of the clasts, and the mechanism by which they were incorporated and mixed with their host material are also considered. Results show that at least five distinct types of clasts occur in LON 94101, of which four have been aqueously altered to various degrees and one is largely anhydrous. The fact that they have had different alteration histories implies that the main part of aqueous activity occurred prior to the mixing and assimilation of the clasts with their host. Further, the presence of such a variety of clasts suggests complex mixing in a dynamic environment involving material from various sources. Two of the clasts, one containing approximately 46 vol% carbonate and the other featuring crystals of pyrrhotite up to approximately 1 mm in size, are examples of unusual lithologies and indicate concentration of chemical elements in discrete areas of the parent body(ies), possibly by flow of aqueous solutions.

Replacement of olivine by serpentine in the Queen Alexandra Range 93005 carbonaceous chondrite (CM2): Reactant–product compositional relations, and isovolumetric constraints on reaction stoichiometry and elemental mobility during aqueous alteration

“…The relatively narrow range of alteration exhibited by serpentine pseudo-alteromorphs after olivine in Nogoya and QUE 93005 contrasts sharply with the much wider range of alteration as determined by other parameters (e.g., carbonate mineral relations) in QUE 93005 (Lee et al, 2012) and LON 94101 (Lindgren et al, 2013). Murray (CM2.4/2.5) contains a number of clasts that experienced severe aqueous alteration contained within a much-less-altered host, suggesting that clasts in Murray were derived from a greater variety of sources (Rubin and Wasson, 1986).…”

“…Arguments favoring alteration of all phases in their present host material (after assembly and lithification of the regolith breccias) require that an aqueous medium within which alteration occurred must have been present during or after the time when all constituents were deposited and lithified into the present rock. The widely observed juxtaposition in some individual CM samples of distinct clasts of lithologies showing different extents of alteration before final assembly militates against hypotheses of postassembly aqueous alteration Lindgren et al, 2013). A scenario in which different volumes of the QUE 93005 parent body experienced different extents of alteration, followed by juxtaposition of lessand more-altered fragments by brecciation after cessation of aqueous alteration was inferred from QUE 93005 by Lee et al (2012), and is supported by the more diverse carbonaceous lithologies in LON 94101 by Lindgren et al (2013).…”

“…Brecciation up to and including regolith brecciation resulted in extensive mechanical clastic mixing of diverse carbonaceous chondrite lithologies, including CM lithologies of varying degrees of aqueous alteration and other carbonaceous chondrite lithologies, in many meteorites (Bunch, 1975;Fodor and Keil, 1976;Bunch et al, 1979;Dodd, 1981;Rubin and Wasson, 1986;Metzler, 1995;Zolensky et al, 1996Zolensky et al, , 1997Nakamura et al, 1999;Brown et al, 2000;Zolensky et al, 2002;Zolensky and Ivanov, 2003;Hutchison, 2004;Bischoff et al, 2006;MacPherson et al, 2009;Herrin et al, 2011;Jenniskens et al, 2012;Prettyman et al, 2012;Lindgren et al, 2013;Greshake, 2014;Hewins et al, 2014).…”

“…Aqueous alteration may have occurred prior to or after accretion and/or re-assembly of the parent body, before or after impact brecciation, and before or after final regolith deposition and (in the case of regolith breccias) lithification of regolith into regolith breccia (e.g., Zolensky et al, 1996;Lee et al, 2012;Lindgren et al, 2013). Arguments favoring alteration of all phases in their present host material (after assembly and lithification of the regolith breccias) require that an aqueous medium within which alteration occurred must have been present during or after the time when all constituents were deposited and lithified into the present rock.…”

The paradox between low shock-stage and evidence for compaction in CM carbonaceous chondrites explained by multiple low-intensity impacts

“…The calcite vein has a fine-scale contortion. LON 94101 has been shown to contain a wide range of clasts with different lithologies (e.g., Lindgren et al, 2013a) each of which could have a different petrofabric.…”