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Interpreting magmatic processes from accessory phases: titanite—a small-scale recorder of large-scale processes

Published online by Cambridge University Press:  03 November 2011

Philip Piccoli
Affiliation:
Laboratory for Mineral Deposits Research, University of Maryland, College Park, Maryland 20742-4211, U.S.A.
Philip Candela
Affiliation:
Laboratory for Mineral Deposits Research, University of Maryland, College Park, Maryland 20742-4211, U.S.A.
Mark Rivers
Affiliation:
Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, U.S.A.

Abstract

In this study we examined variations in ore and other trace-metal concentrations in titanite, a ubiquitous product of magmatic (and subsequent sub-solidus) crystallisation in oxidised silicic magmas. Accessory titanite occurs in the Tuolumne Intrusive Suite (TIS), Sierra Nevada Batholith, as euhedral to anhedral, poikilitic, or interstitial grains. Zoned crystals of titanite were analysed by electron microprobe and synchrotron X-ray fluorescence for major and trace elements. Backscatter electron images reveal zoning, with bright areas correlating positively with total REE concentrations. REE concentrations generally decrease toward the edge of titanite crystals; however, some crystals are reversely zoned, and others exhibit oscillatory or patchy zoning; some grains contain discrete anhedral cores. Most elements in magmatic titanite decrease in concentration towards crystal rims, independent of host rock composition.

At least one major reduction event in the magma chamber(s) transiently stabilised ilmenite, now present only as inclusions in titanite, and resulted in a reduction in the REE concentration in titanite. We suggest the hypothesis that the reduction in the REE concentration in these zones is due to the diminished activity of the (REE)Fe3+ Ca−1Ti−1 exchange component; however, the scatter in the data, together with the operation of other exchange vectors for Fe and Al, did not allow us to test this hypothesis herein. Secondary (i.e. sub solidus, hydrothermal) titanite can be recognised on the basis of its chemistry, sometimes by its anhedral form, and by its position as an alteration rim around primary magmatic phases; however, secondary titanite growth on primary titanite crystals may be harder to discern. Secondary titanite rims on magnetite contain higher Cr, Zr and Mo, and lower REE, relative to magmatic titanite. U/Th ratios increase toward the rim of most titanite grains; however, Th decreases in concentration from core to rim. This is due, most likely, to complications resulting from the coupled substitutions necessary for replacement of Ca by tetravalent Th; factors of this sort are commonly overlooked in trace element analysis.

The analysed titanites are from rocks of the normally zoned TIS which ranges in 87Sr/86Sri, from 0·7059 (tonalite and quartz-diorite) to 0·7066 (granite). Many element ratios in the titanites exhibit little to no functional dependence on 87Sr/86Sri. However, log Mo/W increases with increasing 87Sr/86Sri, of the host unit from the equigranular quartz-diorite and tonalite, to the interior granodiorites, possibly reflecting the greater crustal contribution to the interior, more felsic units. Neither Mo nor W increase significantly from core to rim in titanite. If these trends are indicative of the general behaviour of these elements during in-situ fractionation, then these data suggest that Mo and W are not strongly incompatible, and indeed may behave compatibly, in some titaniteand magnetite-bearing granodioritic magmas.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 2000

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References

Bateman, P. C. 1987. Pre-Tertiary bedrock geologic map of the Mariposa 1° by 2° quadrangle. United States Geological Survey Open File Report 87–670.Google Scholar
Bateman, P. C. 1988. Constitution and genesis of the central part of the Sierra Nevada Batholith, California. United States Geological Survey Open File Report 88–382.Google Scholar
Bateman, P. C. 1992. Plutonism in the Central Part of the Sierra Nevada Batholith, California. United States Geological Survey Professional Paper 1483.Google Scholar
Bateman, P. C., Kistler, R. W., Peck, D. L.& Busacca, A. 1983. Geological map of the Tuolumne Meadows Quadrangle, Yosemite National Park, California. United States Geological Survey Geological Quadrangle Map GQ–1570, 1:62,500.Google Scholar
Bateman, P. C., Chappell, B. W., Kistler, R. W., Peck, D. L.& Busacca, A. 1988. Tuolumne Meadows Quadrangle, California-analytic data. United States Geological Survey Bulletin 1819.Google Scholar
Bateman, P. C.& Chappell, B. W. 1979. Crystallisation, fractionation, and solidification of the Tuolumne Intrusive Series, Yosemite National Park, California. Geological Society of America Bulletin 90, 465–82.Google Scholar
Bence, A. E.& Albee, A.L. 1968. Empirical correction factors for the electron microanalysis of silicates and oxides. Journal of Geology 76, 382403.Google Scholar
Candela, P. A.& Bouton, S. L. 1990. The partitioning of tungsten and molybdenum between silicate melts and ilmenite: implications for F(O2) control of metal ratios in magmatic-hydrothermal W-Mo deposits. Economic Geology 85, 633–40.Google Scholar
Coleman, D. S.& Glazner, A. F. 1997. The Sierran Crest Magmatic Event: Rapid formation of juvenile crust during the late Cretaceous in California. International Geology Review 39, 768–87.Google Scholar
Criss, J. 1977. NRLXRF, Naval Research Laboratory Cosmic Program # DOD-00065. Naval Research Lab, Washington D.C.Google Scholar
Deer, W. A., Howie, R. A.& Zussman, J. 1982. Orthosilicates, Rockforming Minerals, vol. 1A, 2nd ed., 443–66. London: Longman Group Limited.Google Scholar
Drake, M. J.& Weill, D. F. 1972. New rare earth element standards for electron microprobe analysis. Chemical Geology 10, 179–81.Google Scholar
Exley, R. A. 1980. Microprobe studies of REE-rich accessory minerals: implications for the Skye granite petrogenesis and REE mobility in hydrothermal systems. Earth and Planetary Science Letters 48, 97110.Google Scholar
Fleck, R. J., Kistler, R. W.& Wooden, J. L. 1996. Geochronological complexities related to multiple emplacement history of the Tuolumne Intrusive Suite, Yosemite National Park, California. Geological Society of America Abstracts with Programs 28, 65–6.Google Scholar
Fleck, R. J.& Kistler, R. W. 1994. Chronology of multiple intrusion in the Tuolumne Intrusive Suite, Yosemite National Park, Sierra Nevada, California. United States Geological Survey Circular 1107, 101.Google Scholar
Green, T. H. 1994. Experimental studies of trace-element partitioning applicable to igneous petrogenesis—Sedona 16 years later. Chemical Geology 117, 136.Google Scholar
Green, T. H.& Pearson, N. J. 1986. Rare-element partitioning between sphene and coexisting silicate liquid at high pressure and temperature. Chemical Geology 55, 105–19.Google Scholar
Gromet, L. P.& Silver, L. T. 1983. Rare earth element distributions among minerals in a granodiorite and their petrogenetic implications. Geochimica et Cosmochimica Acta 47, 925–40.Google Scholar
Huber, N. K. 1987. The geologic story of Yosemite National Park. United States Geological Survey Bulletin 1595.Google Scholar
Huber, N. K., Bateman, P. C.& Wahrhaftig, C. 1989. Geologic Map of Yosemite National Park and vicinity, California. United States Geological Survey Miscellaneous Investigation Series Map 1–1874.Google Scholar
Jarosewich, E., Nelen, J. A.& Norberg, J. A. 1980. Reference samples for electron microprobe analysis. Geostandards Newsletter 4, 43–7.Google Scholar
Jugo, P. J., Candela, P. A.& Piccoli, P. M. 1999. Linearly independent conditions of chemical equilibrium for the partitioning of ore metals in melt-crystal-volatile phase systems: applications to mineral exploration. Lithos 46, 573–89.Google Scholar
Kistler, R. W., Chappell, B. W., Peck, D. L.& Bateman, P. C. 1986. Isotopic variations in the Tuolumne Intrusive Series, California. Contributions to Mineralogy and Petrology 94, 205–20.Google Scholar
Nakada, S. 1991. Magmatic processes in titanite-bearing dacites, central Andes of chile and Bolivia. American Mineralogist 76, 548–60.Google Scholar
Paterson, B. A., Stephens, W. E.& Herd, D. A. 1989. Zoning in granitoid accessory minerals as revealed by backscattered electron imagery. Mineralogical Magazine 53, 5561.Google Scholar
Paterson, B. A., Rogers, G.& Stephens, W. E. 1992. Evidence for inherited Sm-Nd isotopes in graitoid zircons. Contributions to Mineralogy and Petrology 111, 378.Google Scholar
Paterson, B. A.& Stephens, W. E. 1992. Kinetically induced compositional zoning in titanite: implications for accessory-phase/melt partitioning of trace elements. Contributions to Mineralogy and Petrology 109, 373–85.Google Scholar
Prince, A. T. 1943. The system albite-anorthite-sphene. Journal of Geology 51, 116.Google Scholar
Reid, J. B. Jr, Evans, O. C.& Fates, D. G. 1983. Magma mixing in granitic rocks of the central Sierra Nevada, California. Earth and Planetary Science Letters 66, 243–61.Google Scholar
Ribbe, P. H. 1982. Titanite. In Ribbe, P. H. ed. Reviews in Mineralogy, vol. 5, Orthosilicates, 2nd ed., 137–54. Washington, D.C.: Mineralogical Society of America.Google Scholar
Sawka, W. N., Chappell, B. W.& Kistler, R. W. 1990. Granitoid compositional zoning by side-wall boundary layer differentiation: Evidence from the Palisade Crest Suite, Central Sierra Nevada, California. Journal of Petrology 31, 519–53.Google Scholar
Tacker, R. C.& Candela, P. A. 1987. Partitioning of molybdenum between magnetite and melt; a preliminary experimental study of partitioning of ore metals between silicic magmas and crystalline phases. Economic Geology 82, 1827–38.Google Scholar
Tiller, W. A., Jackson, K. A., Rutter, J. W.& Chalmers, B. 1953. The redistribution of solute atoms during the solidification of metals. Acta Metallurgica 1, 5065.Google Scholar
Toulmin, P. III, & Hammarstrom, J. M. 1990. Geology of the Mount Aetna Volcanic Center, Chaffee and Gunnison Counties, Colorado. United States Geological Survey Bulletin 1864.Google Scholar
Wones, D. R. 1989. Significance of the assemblage of titanite + magnetite + quartz in granitic rocks. American Mineralogist 74, 744–9.Google Scholar
Wyborn, D., Turner, B. S.& Chappell, B. W. 1987. The Boggy Plain Supersuite: A distinctive belt of I-type igneous rocks of potential economic significance in the Lachlan Fold Belt. Australian Journal of Earth Sciences 34, 2143.Google Scholar