Oxygen-Isotope Fractionation between Aluminum-Hydroxide Phases and Water at <60°C: Results of Decade-Long Synthesis Experiments

Cambridge University Press (CUP) - Tập 48 Số 2 - Trang 230-237 - 2000
Frédéric Vitali1, Fred J. Longstaffe1, Michael I. Bird2, W. G. E. Caldwell1
1Department of Earth Sciences, The University of Western Ontario, London, Ontario N6A 5B7, Canada
2Research School of Earth Sciences, The Australian National University, Canberra, A.C.T. 0200, Australia

Tóm tắt

AbstractOxygen-isotope data were obtained for synthetic aluminum-hydroxide phases precipitated over 65–125 mo and have been compared to results from similar experiments conducted for 3–56 mo. The Al(OH)3 polymorphs, gibbsite, nordstrandite, and bayerite, were synthesized, but gibbsite was dominant in most samples, and commonly the only phase present. Using pure gibbsite samples, the following oxygen-isotope fractionation factors, αgibbsite−H2O, were obtained: 1.0167 ± 0.0003 (9 ± 1°C), 1.0147 ± 0.0007 (24 ± 2°C), 1.0120 ± 0.0003 (51 ± 2°C). These values, and the associated equation for an oxygen-isotope geothermometer for the interval 0–60°C 103ln αgibbsite−H2O=2.04×106/T2−3.61×103/T+3.65 (T in K), are not significantly different from those obtained from experiments of much shorter duration. These results, and the good agreement with αgibbsite−H2O values obtained for well-constrained natural systems, suggest that the experimentally determined fractionation factors describe equilibrium conditions for gibbsite that has precipitated directly from solution.As also proposed by others using a modified-increment calculation, our synthesis experiments suggest that αAl(OH)3−H2O is polymorph-dependent at low temperatures and that a significant temperature-dependent trend exists in the values of αAl(OH)3−H2O. However, previously calculated fractionation factors obtained using the modified-increment method are higher than those obtained from the experiments, with this discrepancy becoming larger as temperature decreases.

Từ khóa


Tài liệu tham khảo

10.1016/0016-7037(90)90172-H

Yapp, 1993, Climate Change in Continental Isotopic Records, 285

Schoen, 1970, Structures of aluminum hydroxides and geochemical implications, American Mineralogist, 55, 43

10.1351/pac199466020273

10.1016/0009-2541(88)90085-X

10.1016/0016-7037(71)90017-2

10.1016/0016-7037(63)90071-1

10.1016/0016-7037(94)90310-7

10.1016/0016-7037(72)90068-3

10.1515/9781501508998-012

Davis, 1974, Occurrence of nordstrandite and its possible significance in Jamaica bauxite, Travaux Commission Internationale Etude Bauxites Alumine Alum. ICSOBA, 11, 61

Chen, 1990, Comment on “A stable-isotope study of lateritic bauxite” by M.I. Bird, A.R. Chivas, and A.S. Andrew, Geochimica et Cosmochimica Acta, 54, 1483, 10.1016/0016-7037(90)90171-G

10.1016/0016-7037(89)90073-2

10.1016/0016-7037(53)90051-9

Bernard, 1976, Détermination des rapports isotopiques 18O/16O de la gibbsite et de la boehmite présentes dans differentes bauxites, Comptes Rendus Académie Sciences Paris, 282, 1089

10.1007/s002690050105

10.1016/0016-7037(92)90362-M

Bernard, 1978, Composition isotopique des minéraux secondaries des bauxites. Problèmes de genèse

10.2136/sssaj1966.03615995003000020011x

Jackson, 1975, Soil Chemical Analysis Advanced Course

10.1180/minmag.1971.038.295.11

Goldbery, 1970, Dawsonite and nordstrandite in the Permian Berry Formation of the Sydney Basin, New South Wales, American Mineralogist, 55, 477

10.1016/0016-7037(93)90295-8

10.1038/196265a0

Hsu, 1989, Minerals in Soil Environments, 331

10.1038/196264b0

10.1180/minmag.1963.033.263.14

Thông tin
Thông tin xuất bản

Cambridge University Press (CUP)

Tập 48 Số 2

230-237

Thông tin tác giả