scholarly journals Low temperature aqueous alteration of basalt: Mineral assemblages of Deccan basalts and implications for Mars

2012 ◽  
Vol 117 (E11) ◽  
pp. n/a-n/a ◽  
Author(s):  
R. N. Greenberger ◽  
J. F. Mustard ◽  
P. S. Kumar ◽  
M. D. Dyar ◽  
E. A. Breves ◽  
...  
Keyword(s):  
Low Temperature ◽  
Aqueous Alteration ◽  
Mineral Assemblages

Diagenesis and low-temperature metamorphism of Mt. Medvednica, Croatia: Mineral assemblages and phyllosilicate characteristics

2004 ◽  
Vol 47 (2-3) ◽  
pp. 151-176 ◽  
Author(s):  
Katalin Judik ◽  
Péter Árkai ◽  
Péter Horváth ◽  
Gábor Dobosi ◽  
at al.
Keyword(s):  
Low Temperature ◽  
Mineral Assemblages

Crustal geochemistry in the Wawa–Foleyet region, Ontario

1994 ◽  
Vol 31 (7) ◽  
pp. 1104-1121 ◽  
Author(s):  
D. M. Shaw ◽  
A. P. Dickin ◽  
H. Li ◽  
R. H. McNutt ◽  
H. P. Schwarcz ◽  
...  
Keyword(s):  
Low Temperature ◽  
Continental Crust ◽  
Major Elements ◽  
Chemical Compositions ◽  
Transition Elements ◽  
Aqueous Alteration ◽  
Clastic Sediments ◽  
Greenstone Belts ◽  
Regional Abundance ◽  
Fluid Homogenization

Fifty-three rock samples from the Kapuskasing structural zone (KSZ) and 56 from the Wawa domal gneiss terrane (WGT), Ontario, have been analysed for major elements, 32 trace elements, and δ18O; δD was measured in a few samples.Average chemical compositions for the KSZ and WGT regions have been calculated from map unit averages weighted by regional abundance. Compared with estimates of the composition of the upper continental crust (UCC), the KSZ is enriched in Al, Fe, Mg, Ca, P, transition elements, Sc, and Sr; depleted in Si, B, most rare earth elements, Zr, Hf, Nb, Ta, Li, Na, K, U, Th, Ba, and Rb; but similar in composition to estimates of the lower continental crust. The WGT is closer in composition to the UCC. These data support the interpretation, on geophysical and petrological grounds, that the crust here is layered and has been uplifted, the WGT and KSZ regions representing progressively deeper levels.Igneous rock and orthogneiss δ18O values in the KSZ and WGT show good correlation with the weight percentages of SiO2. Paragneisses and clastic sediments and metavolcanics in the Michipicoten greenstone belt have higher ratios, as in other greenstone belts. Low δ18O and high δD values in most of the higher grade mafic gneisses show that they have never undergone low-temperature marine alteration. However, a few mafic gneisses with relict pillows show δ18O and δD values indicating low-temperature aqueous alteration. The δ18O and δD evidence throughout the two regions supports the view that no regional fluid homogenization took place.Errorchron ages of 2725 ± 130 Ma (Rb/Sr) and 2755 ± 110 Ma (Sm/Nd) were obtained for tonalite–granodiorite gneiss and agree within error with results from other workers. The intrusive Floranna Lake complex is 2580 ± 120 Ma (Rb/Sr), not significantly different from the age of the tonalite. Scatter in the data is to be attributed to localized late-stage alteration under low water–rock ratios by Sr-rich–Rb-poor brines. Model Nd ages suggest that there is no old crust [Formula: see text] in the region and that the 2700 Ma mantle was depleted relative to the bulk earth.

scholarly journals Exogenous copper sulfide in returned asteroid Itokawa regolith grains are likely relicts of prior impacting body

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Katherine D. Burgess ◽  
Rhonda M. Stroud
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Low Temperature ◽  
Copper Sulfide ◽  
Parent Body ◽  
Carbonaceous Chondrites ◽  
Aqueous Alteration ◽  
Thermal Alteration ◽  
Transmission Electron ◽  
Rubble Pile

AbstractSamples from asteroid 25143 Itokawa returned by the Hayabusa mission have been identified as LL4-6 ordinary chondrite materials and have shown it to be a rubble pile that aggregated after break-up of a parent body. Here we investigate particle RB-CV-0038 from the Itokawa regolith using scanning and transmission electron microscopy and energy dispersive spectroscopy. We identify a cubanite-chalcopyrite-troilite-pyrrhotite assemblage, the phases and structure of which are indicative of low-temperature, aqueous alteration. Cubanite is stable only at temperatures below around 250 °C and has thus far only been identified in CI carbonaceous chondrites and the comet 81P/Wild2 sample suite. Chalcopyrite is also very rare in the meteorite record and is found mostly in R chondrites and some CK chondrites. Because the Itokawa parent body experienced significant thermal alteration with little evidence of low-temperature equilibration or aqueous alteration, we propose that the assemblage we identify is most likely exogenous and represents a component of an impacting body.

Phase Equilibria in the System MgO-Al2O3-SiO2-H2O: Chlorites and Associated Minerals

1973 ◽  
Vol 39 (303) ◽  
pp. 297-312 ◽  
Author(s):  
Bruce Velde
Keyword(s):  
Solid Solution ◽  
Chemical Composition ◽  
Low Temperature ◽  
Phase Equilibria ◽  
Water Pressure ◽  
Positive Slope ◽  
Natural Mineral ◽  
Natural Minerals ◽  
Cell Dimensions ◽  
Mineral Assemblages

SummaryTwenty-six compositions in the system MgO-Al2O3-SiO2-H2O were investigated under conditions of 1 and 2 Kb water pressure and temperatures between 300 and 700°C. The solid solution for 7 Å and 14 Å chlorites has been delimited as well as that of the expanding phases (tri- and dioctahedral montmorillonites and expanding chlorites). Negative slopes were found for the transformation montmorillonite → expanding chlorite, and expanding chlorite → chlorite+quartz and a positive slope for 7Å → 4 Å transformation. The relative positions of the reactions chlorite+quartz → cordierite+talc, chlorite+andalusite → cordierite and chlorite+corundum → cordierite+spinel are located between 500 and 65°C.Cell dimensions of the synthetic chlorites can be correlated with their chemical composition. Solid solution in synthetic minerals compares well with 325 analysis of natural minerals from the literature, indicating that the chemiographic relations between phases in the simplified synthetic system are applicable to natural mineral assemblages. The phase relations indicate that at low temperature the 7Å aluminous chlorite is not stable with quartz or another silica phase.

The precursor principle and the possible significance of stratiform ores and related chemical sediments in the elucidation of processes of regional metamorphic mineral formation

1989 ◽  
Vol 328 (1602) ◽  
pp. 529-646 ◽  
Keyword(s):  
Low Temperature ◽  
Regional Metamorphism ◽  
Mineral Chemistry ◽  
Metamorphic Grade ◽  
Island Arc ◽  
Calc Alkaline ◽  
Diagenetic Alteration ◽  
Metamorphic Mineral ◽  
Mineral Assemblages ◽  
Chemical Sediments

This contribution is concerned with the regional metamorphism of fine-grained (pelitic) sedimentary materials, and with the pelitic components of coarser sediments. It emphasizes the possible importance of purely chemical sedimentary rocks, and the preservation of chemical patterns within them, in the elucidation of some regional metamorphic mineralogical processes. The materials and examples used come largely from the category of exhalative sediments, of which stratiform metallic sulphide orebodies and their associated exhalites are important members. A few examples come from volcanic rocks that have been altered by exhalative processes. The special significance of chemical sediments stems from their propensity for the development of highly complex metamorphic silicate mineral assemblages within relatively minuscule volumes of rock, and from their commonly sharply defined chemical bedding and chemical sedimentary facies patterns. As the primary nature of such chemical bedding and chemical layering and zoning in completely unmetamorphosed materials is observable and known, and as their sharp boundaries and other well-defined features can be examined in a full range of unmetamorphosed to highly metamorphosed environments, they may be used as extremely sensitive markers for the detection and measurement of any chemical movement that may have taken place during regional metamorphism. Detailed examination of such evidence appears to indicate a general lack of diffusion and reaction, and a common lack of attainment of mineral equilibrium, in the development of the regional metamorphic silicate assemblages of a number of such stratiform ore deposits and their associated exhalative materials. This, together with the common interbedded nature of metamorphic silicate, sulphide, carbonate, etc., and the faithful maintenance of primary sedimentary chemical facies patterns within many exhalative metasediments suggests that the silicates, like the accompanying sulphides and associated compounds, may derive directly and in situ from early-formed precursor materials rather than from extensive elemental diffusion and metamorphic reaction. That particular clays and zeolites derive from specific precursors in many instances has been recognized for a long time. That many metamorphosed bedded oxides (including quartz), together with carbonates, sulphates, sulphides and authigenic silicates such as the feldspars, have derived from sedimentary: diagenetic precursors is self-evident and unavoidable, and establishes precursor derivation for at least some regional metamorphic minerals as a principle, not an hypothesis. What is not known, however, is the extent to which this principle applies to the broader spectrum of metamorphic silicates. The present contribution examines this problem. The evidence of ‘ metamorphic ’ silicates in a range of unmetamorphosed and littlemetamorphosed rocks, in present ocean-floor sediments, in unmetamorphosed volcanic alteration products and in modern geothermal systems is examined. The preservation of possible precursor materials in a variety of rocks, and the synthesis of a number of ‘ metamorphic ’ minerals by low-temperature solution experimentation and in low-temperature industrial products is considered. It is deduced that most of the well-known regional metamorphic minerals may in fact be produced directly from low-temperature sedimentary/diagenetic/alteration materials, and that such precursors may be of simple or complex kind. It is suggested that the direct derivation of regional metamorphic silicates from precursors may resolve the problem of the elusive metamorphic mineral reaction, and that the principal regional metamorphic grade indicators may be the temperatures of precursor transformations rather than temperatures of reactions. Several implications of the precursor principle are then examined: its significance in the interpretation of zoning of regional metamorphic mineral assemblages and mineral chemistry; in considerations of metamorphic grade and the development of grainsize; in the identities of certain metamorphic equilibria, intergrowths and ‘retrograde’ materials; and in the deduction of earlier environments of rock formation and alteration. In this general connection it is proposed that the overall regional metamorphic process may be substantially indigenous: that through their primary nature certain materials, e.g. some andesitic-dacitic volcaniclastic rocks, may be predisposed to metamorphose themselves, and that this may be accentuated by the petro-tectonic setting in which they form, e.g. island arc - eugeosynclinal provinces, with their characteristically inter-related calc-alkaline volcanism, riftrelated palaeogeographical features and highly patterned heat flow. Effects of climate may be superimposed on this: some of the more highly developed regional metamorphic zoning may arise in calc-alkaline volcanic sediments deposited in tropical island arc shelf areas, and in sediments laid down in large saline lakes of continental volcanic rift provinces. From all this it is proposed that the ambit of regional metamorphic petrology may be much wider than currently visualized. Just as precursor-derived oxides, carbonates, sulphates, graphite, pyrite, etc., of high-grade metasedimentary rocks may give clear indications concerning the nature and environments of formation of the original sediments, so the metamorphic silicates may yield subtle insights into palaeoprovenance, palaeogeography, palaeoclimate and a variety of weathering, volcanic alteration, sea-floor hydrothermal and other regimes. The application of metamorphic mineralogy and mineral chemistry to the search for stratiform ores in metamorphosed terranes may constitute one of the major advances in mineral exploration in the near future. It appears that there is considerable scope for further searching for possible precursor material in a variety of rocks and modern sediments (especially those of the present-day volcanic-sedimentary milieu), extension of clay and mixed-layer clay-chlorite-zeolite mineral synthesis in low-temperature-pressure laboratory experiment, and for the investigation of the behaviour of these synthetic products at metamorphic temperatures and pressures.

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