Hydrothermal Experiments on Refractory Minerals Related to CAIs: Implications for Aqueous Alteration in Parent Bodies

Details Hydrothermal Experiments on Refractory Minerals Related to CAIs: Implications for Aqueous Alteration in Parent Bodies Hydrothermal Experiments on Refractory Minerals Related to CAIs: Implications for Aqueous Alteration in Parent Bodies

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.558n&link_type=abstract

Meteoritics, vol. 30, no. 5, page 558

Other

Aqueous Alteration, Calcium Aluminum-Rich Inclusions, Chondrites, Carbonaceous, Hydrothermal Experiments, Meteorites, Murchison, Yamato 791717, Nepheline

Scientific paper

Ca-Al-rich inclusions (CAIs) in carbonaceous chondrites contain secondary minerals such as nepheline, calcite and phyllosilicates [1]. There is no consensus on whether secondary minerals were produced by reaction with a solar nebular gas [2] or by aqueous alteration in parent bodies [3]. We performed hydrothermal experiments on several minerals common in CAIs to study aqueous alteration in parent bodies. Experiments: Hydrothermal experiments in this study were divided into two categories. The first category was the experiments with three refractory minerals, gehlenite (melilite), diopside and spinel as starting materials. The second one was the experiments done on assumption of further alteration of gehlenite from the first experiments with amorphous Al-Si ( decomposed gehlenite with a 1N HCl solution ). Gehlenite and diopside were synthesized in our laboratory. Spinel that is commercially produced was used for this study. We used both powder samples for characterization by X-ray diffraction and pellets for observation by a scanning electron microscope. Results: Gehlenite was decomposed to hydrogrossular [Ca3Al2(SiO4,OH)3] and acicular Ca-Si material (probably xonotlite [Ca6Si6O17(OH)2] or wollastonite) in a 1N NaOH solution. In a 1N Na2CO3 solution, gehlenite was decomposed to calcite and (hydro) sodalite. Gehlenite was decomposed to amorphous Al-Si in a 1N HCl solution. This may be related to formation of phyllosilicates in CAIs. Analcime [NaAlSi2O6 H2O] was produced easily from amorphous Al-Si (decomposed gehlenite with a 1N HCl solution) in the second experiments. Analcime has close relations with nepheline. Diopside and spinel were not affected in all run conditions (1N NaOH, Na2CO3 and HCl). The pH of solutions changed from 0.97 to 3.95 in case of 0.1N HCl with gehlenite and from 2.15 to 11.00 in case of 0.01N HCl. Discussion: We propose from this work that secondary minerals in CAIs were produced by aqueous alteration in parent bodies only from gehlenite. We could get hydrogrossular, acicular Ca-Si material, calcite, amorphous-Al-Si, analcime and sodalite from gehlenite in our experiments. These minerals are included in CAIs or have relations with minerals included in CAIs. Durability against hydrothermal alteration of minerals in our experiments suggests a similar trend to susceptibility to alteration of primary minerals included in CAIs [4]. The results that only gehlenite was altered are consistent with those of observations that gehlenite seems to be the most susceptible to alteration [4]. Elevation of pH of 0.1N and 0.01N solution with gehlenite was probably due to leaching of Ca from the surfaces of gehlenite grains. We attempt to extend these results into how gehlenite in CAIs was converted into nepheline and/or sodalite. Calcite and feldspathoid rich in sodium coexist in CAIs in the Murchison CM chondrite [5]. In our experiments, gehlenite in a Na2CO3 solution was converted into calcite and sodalite. In this case, Ca was extracted from gehlenite due to a high chemical potential of CO2 and calcite was produced. Al and Si ( residue of decomposed gehlenite by the Ca extraction ) reacted with Na in a fluid to form feldspathoid. However, nepheline and/or sodalite that do not coexist with calcite are often observed. For example, CAIs in Yamato 791717 have a core of gehlenite and spinel, mantled by nepheline, fassaite and diopside. These textures suggest that nepheline formed by replacing mainly gehlenite [6]. The most likely explanation is that nepheline and/or sodalite were produced by two stage aqueous alteration mainly from gehlenite in the parent body. In the first stage of aqueous alteration, gehlenite was decomposed to Al-Si material by leaching of Ca. At this stage, this leaching of Ca and that of Na from matrix glassy materials elevated the pH of the fluid. At a later stage, Al-Si material reacted with Na in the fluid and converted into nepheline and/or sodalite under higher pH condition. Spienl and diopside did not react with Na in the fluid at this later stage. References: [1] Lee M. R. and Greenwood R. C. (1994) Meteoritics, 29, 780-790. [2] Grossman L. and Steele I. M. (1976) GCA, 40, 149-155. [3] Greenwood R. C. et al. (1994) GCA, 58, 1913-1935. [4] MacPherson G. J. et al. (1988) in Meteorites and the Early Solar System (J. F. Kerridge and M. S. Matthews, eds.), 746-807. [5] MacPherson G. J. et al. (1983) GCA, 47, 823-839. [6] Tomeoka K. et al. (1992) Meteoritics, 27, 136-143.

Affiliated with

Also associated with

No associations

Rating

Hydrothermal Experiments on Refractory Minerals Related to CAIs: Implications for Aqueous Alteration in Parent Bodies does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Hydrothermal Experiments on Refractory Minerals Related to CAIs: Implications for Aqueous Alteration in Parent Bodies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrothermal Experiments on Refractory Minerals Related to CAIs: Implications for Aqueous Alteration in Parent Bodies will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-830233