Three phases of carbonate minerals and two degrees of alteration in the Nogoya CM2 carbonaceous chondrite

No abstract available

Serpentinisation of Chondrules in the Murchison Cm Carbonaceous Chondrite by Centripetal Replacement and Cementation [abstract]

No abstract available

Formation of Berthierine in the Martian Meteorite Nakhla by Replacement Of Aluminosilicate Glass [abstract]

No abstract available

Glassy chondrule mesostasis in EET 96029: a CM3 component of a minimally altered CM2 carbonaceous chondrite

No abstract available

Tracking the Earliest Stages of Aqueous Alteration in the Mildly Altered CM Chondrite EET 96029

The earliest stages of CM carbonaceous chondrite aqueous alteration are very poorly understood as mildly altered CMs are extremely rare. The Paris meteorite (CM2.7) [1-3] and QUE 97990 (CM2.6) [4,5] are among the least aqueously altered CMs described to date. However, neither of them contain the pristine attribute of chondrule mesostasis glass. Glass is highly reactive and so among the very first phases to undergo aqueous alteration [6]. Therefore, the CM carbonaceous chondrite EET 96029 is very unusual as it has been shown to have retained mesostasis glass in at least one chondrule [7]. According to the new CM classification scheme of [8], which is based on H content, EET 96029 has an index of 2.0 (data in [9]), meaning that it is less altered than all but one of the fifty CMs analysed by [8]. A caveat is that a low H content could be due to mild heating as well as a low degree of aqueous processing [9]. However, the bulk O oxygen isotope composition of EET 96029 (as determined by [10]) is consistent with a low degree of alteration as it is slightly closer to that of the CO3 falls (possible representatives of the anhydrous progenitors of the CMs) than even the least altered lithology of Paris (Fig. 1).<p></p> To better understand the earliest stages of CM aqueous alteration and its impact on mesostasis glass, we have undertaken a detailed study of chondrule mesostasis textures and compositions in the mildly aqueously altered CM chondrite EET 96029.<p></p&gt

Dating climatic change in hot deserts using desert varnish on meteorite finds

A thin coating of desert varnish occurs on Forrest 009 and Nurina 004, both equilibrated ordinary chondrite (L6) finds from the Nullarbor Plain, Australia. This finely laminated deposit is chemically and petrographically comparable to the varnish found on terrestrial rocks. Forrest 009, which has a terrestrial age of 5.9 kyr, has a 100-130 micrometre thick coating of desert varnish that has a laterally consistent chemical microstratigraphy comprising a narrow Ba- and Mn-poor lower region, a thick Ba- and Mn-rich central area and a narrow outer zone almost devoid of both cations. The interior of the meteorite contains Fe-oxide and oxyhydroxide veins that have formed by chemical weathering of metals and sulphides. As these veins do not cross-cut the varnish, it must have accreted rapidly relative to the weathering rate of the meteorite. The less than or equal to 70 mum thick varnish on Nurina 004, which has a terrestrial age of 33.4 kyr, lacks a consistent chemical microstratigraphy, but it is cross-cut by Fe-oxide and oxyhydroxide veins, some of which have supplied Fe to the varnish. This implies that the chemical weathering rate of Nurina 004's interior was slow in comparison to the accretion rate of the varnish. The petrography and chemical composition of varnish on Forrest 009 indicates that this meteorite may have resided in a relatively humid environment for most of its 5.9 kyr terrestrial history and that the Nullarbor recently became more arid. This conclusion supports results from an analysis of Fe-bearing weathering products in the interior of the meteorite by Mossbauer spectroscopy, which also indicate that Forrest 009 experienced an early period of rapid weathering under relatively humid conditions. The petrography of varnish on Nurina 004 shows that the interior of the meteorite weathered relatively slowly, probably because it fell during an and time, which is again in agreement with previous Mossbauer spectroscopy results. Results from both meteorites are in agreement with palaeoclimate data derived from a number of other proxies. The implications of this work are that the large number of meteorites that have been collected from several hot deserts of the world may be a powerful source of information on climate change over the last 30-35 kyr

Martian Fluid Evolution Recorded in Smectite from the Northwest Africa (Nwa) 817 Nakhlite Meteorite [abstract]

No abstract available

Evidence for Localized High Temperature Hydrothermal Fluid Flow within the Sub-Crater Environment of the Rochechouart Impact Structure: Observations from a Polymict Breccia Dike

Hypervelocity impacts into volatilebearing terrestrial targets can initiate hydrothermal circulation for a finite period of time; evidence for this is preserved in approximately one-third of impact structures on Earth [1, 2]. Hydrothermal environments can host extremophile life, and microbial communities have been found to colonize impact craters [3, 4]. The majority of impact structures on Earth have yet to be studied in great detail; many aspects of the post-impact environment such as the extent and duration hydrothermal circulation with respect to location within the structure as well as crater diameter, target composition and external influences, (paleogeography) are not fully understood. <p></p>We present evidence for high temperature hydrothermal fluid circulation within the sub-crater environment of the highly eroded, 23km diameter, Mesozoic Rochechouart impact structure located in west-central France [5]. This evidence is a new impact lithology that was found during a recent field campaign at a collection site located approximately 7.5km north-east of the structure's center. It is a highly porous, polymict lithic impact breccia dike containing carbonate mineralization found below the transient crater floor. Secondary hydrothermal mineral assemblages are diagnostic of a range of temperatures (>100°C to low temperature diagenetic).<p></p&gt