Topic
Iddingsite
About: Iddingsite is a research topic. Over the lifetime, 114 publications have been published within this topic receiving 3764 citations.
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TL;DR: The seven nakhlite meteorites are augite-rich igneous rocks that formed in flows or shallow intrusions of basaltic magma on Mars as discussed by the authors, and they consist of euhedral to subhedral crystals of augite and olivine (to 1 cm long) in fine-grained mesostases.
Abstract: The seven nakhlite meteorites are augite-rich igneous rocks that formed in flows or shallow intrusions of basaltic magma on Mars. They consist of euhedral to subhedral crystals of augite and olivine (to 1 cm long) in fine-grained mesostases. The augite crystals have homogeneous cores of Mg' = 63% and rims that are normally zoned to iron enrichment. The core-rim zoning is cut by iron-enriched zones along fractures and is replaced locally by ferroan low-Ca pyroxene. The core compositions of the olivines vary inversely with the steepness of their rim zoning - sharp rim zoning goes with the most magnesian cores (Mg' = 42%), homogeneous olivines are the most ferroan. The olivine and augite crystals contain multiphase inclusions representing trapped magma. Among the olivine and augite crystals is mesostasis, composed principally of plagioclase and/or glass, with euhedra of titanomagnetite and many minor minerals. Olivine and mesostasis glass are partially replaced by veinlets and patches of iddingsite, a mixture of smectite clays, iron oxy-hydroxides and carbonate minerals. In the mesostasis are rare patches of a salt alteration assemblage: halite, siderite, and anhydrite/ gypsum. The nakhlites are little shocked, but have been affected chemically and biologically by their residence on Earth. Differences among the chemical compositions of the nakhlites can be ascribed mostly to different proportions of augite, olivine, and mesostasis. Compared to common basalts, they are rich in Ca, strongly depleted in Al, and enriched in magmaphile (incompatible) elements, including the LREE. Nakhlites contain little pre-terrestrial organic matter. Oxygen isotope ratios are not terrestrial, and are different in anhydrous silicates and in iddingsite. The alteration assemblages all have heavy oxygen and heavy carbon, while D/H values are extreme and scattered. Igneous sulfur had a solar-system isotopic ratio, but in most minerals was altered to higher and lower values. High precision analyses show mass-independent fractionations of S isotopes. Nitrogen and noble gases are complex and represent three components: two mantle sources (Chas-E and Chas-S), and fractionated Martian atmosphere. The nakhlites are igneous cumulate rocks, formed from basaltic magma at approx.1.3 Ga, containing excess crystals over what would form from pure magma. After accumulation of their augite and olivine crystals, they were affected (to various degrees) by crystallization of the magma, element diffusion among minerals and magma, chemical reactions among minerals and magma, magma movement among the crystals, and post-igneous chemical equilibration. The extent of these modifications varies, from least to greatest, in the order: MIL03346, NWA817, Y000593, Nakhla = Governador Valadares, Lafayette, and NWA998. Chemical, isotopic, and chronologic data confirm that the nakhlites formed on Mars, most likely in thick lava flows or shallow intrusions. Their crystallization ages, referenced to crater count chronologies for Mars, suggest that the nakhlites formed on the large volcanic constructs of Tharsis, Elysium, or Syrtis Major. The nakhlites were suffused with liquid water, probably at approx.620 ma. This water dissolved olivine and mesostasis glass, and deposited iddingsite and salt minerals in their places. The nakhlites were ejected from Mars at approx.10.75Ma by an asteroid impact and fell to Earth within the last 10,000 years. Although the nakhlites are enriched in incompatible elements, their source mantle was strongly depleted. This depletion event was ancient, as the nakhlites source mantle was fractionated while short-lived radionuclides (e.g., t(sub 1/2 = 9 my) were still active. This differentiation event may have been core formation coupled with a magma ocean, as is inferred for the moon.
324 citations
TL;DR: In this article, the authors suggest that the most plausible models for secondary mineral formation involve the evaporation of low temperature (25 - 150 °C) brines, which is consistent with the simple mineralogy of these assemblages, Fe-Mg-Ca carbonates, anhydrite, gypsum, halite, clays.
Abstract: The SNC (Shergotty-Nakhla-Chassigny) meteorites have recorded interactions between martian crustal fluids and the parent igneous rocks. The resultant secondary minerals — which comprise up to ~1 vol.% of the meteorites — provide information about the timing and nature of hydrous activity and atmospheric processes on Mars. We suggest that the most plausible models for secondary mineral formation involve the evaporation of low temperature (25 – 150 °C) brines. This is consistent with the simple mineralogy of these assemblages — Fe-Mg-Ca carbonates, anhydrite, gypsum, halite, clays — and the chemical fractionation of Ca-to Mg-rich carbonate in ALH84001 “rosettes”. Longer-lived, and higher temperature, hydrothermal systems would have caused more silicate alteration than is seen and probably more complex mineral assemblages. Experimental and phase equilibria data on carbonate compositions similar to those present in the SNCs imply low temperatures of formation with cooling taking place over a short period of time (e.g. days). The ALH84001 carbonate also probably shows the effects of partial vapourisation and dehydration related to an impact event postdating the initial precipitation. This shock event may have led to the formation of sulphide and some magnetite in the Fe-rich outer parts of the rosettes.
302 citations
TL;DR: In this article, the authors describe the larger scale aspects of the weathering of several southeastern Australian basalts on samples taken from the fresh, rounded, core-stone out to the edge of the surrounding coherent weathering rinds and discuss the changes in bulk-rock chemistry and mineralogy that accompanied this early weathering.
Abstract: The weathering of eastern Australian basalts, sampled from the rounded, hard, core-stone to the rind of softer weathered material, has been examined by bulk chemical analyses, thin section pe- trography, electron microprobe, and X-ray powder diffraction analyses. Using density as a measure of weathering intensity, data from four core-stones show that at a stage of weathering in which the total loss due to dissolution is I/3 (i.e., at the core-stone rim), the percentages lost of the following major elements are: Ca, 85; Mg, 80; Na, 70; K, 50-80; P, 55; Si, 45; Mn, 40; A1, 5; Fe, 0; and Ti, 0. With more intense weathering, deposition of some elements, particularly rare earths and Ba, and mobilization and deposition of A1 and Fe make quantification impossible. The rate of weathering of individual minerals is consistent with the well-known susceptibility series: glass ~ olivine > plagioclase > pyroxene > opaque minerals. Clay minerals in the core-stones are dominated by smectites, whereas those in the surrounding more intensely weathered rinds are dominated by halloysite and goethite. The investigations described in this and succeeding papers of this series were conducted to understand the mechanism of basalt weathering by examining the pro- cess at the maximum available resolution. Optical mi- croscopic, X-ray powder diffraction, transmission and scanning electron microscopic, bulk chemical, energy- dispersive X-ray, electron microprobe, and various other analytical techniques were used to trace mineral alterations and to evaluate these alterations within a broader framework of the bulk changes occurring in the whole rock during the weathering process. The present paper describes the larger scale aspects of the weathering of several southeastern Australian basalts on samples taken from the fresh, rounded, core- stone out to the edge of the surrounding coherent weathering rinds and discusses the changes in bulk- rock chemistry and mineralogy that accompanied this early weathering. Later papers will present detailed ex- aminations of the alteration of individual minerals, including the weathering of olivine to iddingsite and bowlingite and the weathering of plagioclase, pyroxene, and opaque oxides. BACKGROUND
290 citations
TL;DR: This paper used the ages of secondary alteration minerals in Martian meteorites to obtain absolute ages when liquid water was at or near the surface of Mars, and showed that water very efficiently fractionates I from Xe, raising the intriguing possibility that Mars had a liquid water ocean within its first 100 Myr.
Abstract: [1] There is widespread photogeological evidence for ubiquitous water flowing on the surface of Mars. However, the age of surface and near-surface water cannot be deduced with high precision from photogeology. While there is clear evidence for old and young fluvial features in the photogeologic record, the uncertainty in the absolute calibration of the Martian crater flux results in uncertainties of ±1.5 Gyr in the middle period of Martian geologic history. Aqueous alteration of primary igneous minerals produces secondary minerals in Martian meteorites. Here we use the ages of secondary alteration minerals in Martian meteorites to obtain absolute ages when liquid water was at or near the surface of Mars. Aqueous alteration events in Martian meteorites occurred at 3929 ± 37 Ma (carbonates in ALH84001), 633 ± 23 Ma (iddingsite in nakhlites), and 0–170 Ma (salts in shergottites). Furthermore, these events appear to be of short duration, suggesting episodic rather than continuous aqueous alteration of the meteorites. The Martian meteorites appear to be contaminated by Martian surface Pb characterized by a 207Pb/206Pb ratio near 1. Lead of this composition could be produced by water-based alteration on the Martian surface. The high 129Xe/132Xe ratio in the Martian atmosphere compared to Martian meteorites indicates fractionation of I from Xe within ∼100 Myr after nucleosynthesis of 129I. Such fractionation is difficult to achieve through magmatic processes. However, water very efficiently fractionates I from Xe, raising the intriguing possibility that Mars had a liquid water ocean within its first 100 Myr.1.
134 citations
TL;DR: In this paper, heavy-mineral analyses of fifty Quaternary sediments from the North Sea, Red Sea, East China Sea, South China Sea and Vancouver Island area (western seaboard of Canada) supplemented by over 1000 published analyses of sediment from many other sites in the world define accessory clastic mineral assemblages indicative of the principal plate-tectonic settings (excluding transform plate boundaries) associated with continental margins.
Abstract: Heavy-mineral analyses of fifty Quaternary sediments from the North Sea, Red Sea, East China Sea, South China Sea, and Vancouver Island area (western seaboard of Canada) supplemented by over 1000 published analyses of sediments from many other sites in the world define accessory clastic mineral assemblages indicative of the principal plate-tectonic settings (excluding transform plate boundaries) associated with continental margins. Assemblages of all continental margins studied differ significantly from those of the intraoceanic, island-arc, and deep marginal-sea assemblages by possessing relatively high contents of zircon, tourmaline, garnet, epidote, amphibole (as well as other less common minerals), derived chiefly from metamorphic and sialic intrusive rocks. This suite is accompan ed by olivine, iddingsite, and brown (titanium-rich) clinopyroxene in regions containing rifting-type volcaniclastic sediments (i.e., near divergent plate boundaries), and with orthopyroxene, green clinopyroxene, and green-brown hornblende in arc-type volcaniclastic deposits (areas near convergent plate boundaries). On passive continental margins, both volcaniclastic suites are absent or present in negligible amounts.
114 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 6 |
| 2020 | 3 |
| 2019 | 2 |
| 2018 | 3 |
| 2017 | 1 |
| 2016 | 4 |