Petrologic studies

From our particular perspective, the goals of petrologic studies are determination of how, in the context of a given rock bulk composition, the intensive variables interrelate with the chemistry, polytypism, textural, and physical aspects of the minerals (primarily the white micas) in metamorphic rocks. In principle, if the minerals are in chemical equilibrium, or at least close thereto, interrelationships among mineral chemistry, bulk composition and intensive variables should be well defined inasmuch as they are constrained by the laws of chemistry. The interrelationships involving the intensive parameters and polytypism, textures, and physical aspects of the minerals may be less well defined because the laws controlling them are less well understood. Our emphasis is primarily on the mineral chemistry and secondarily on polytypism and some physical aspects like the elastic constants. 

Twenty or thirty years ago arguments indicating that the rocks being studied have approached chemical equilibrium were an important part of all metamorphic petrology 

In addition to the above outlined equilibrium problem, some key, mineralogy-related difficulties occur which may prevent attaining of the goals of petrologic studies. They include they include the following, largely interrelated topics  

Although the fundamental thermodynamic data for the end-member phases and systems relevant to common rocks now seems to be quite adequate (e.g., Berman 1988 or Holland and Powell 1998), some serious gaps still exist for quantitative treatment of equilibria in mixed composition space. In particular, at least for the micas, there is a dearth of data needed for quantitative treatment of the specific, common equilibria that occur in nature. Reasons for this dearth will be discussed below in the Mineralogic studies sub-section. At least three missing data sets that can be listed for the micas  

Obviously, activity models must reflect these sorts of interactions among and between sites. In some cases (Powell and Holland 1998) activity models have been proposed for micas to reflect these types of complex interactions, but as yet they seem to be largely theoretical constructs with little in the way of direct testing of the validity of the models. 

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Lazzarini, L., G. Moschini, and B. M. Stievano (1980), A contribution to the identification of Italian, Greek and Anatolian marbles through a petrological study and the evaluation of the Ca/Sr ratio, Archaeometry 22,173-183. 

Russell SS, Huss GR, Fahey AJ, Greenwood RC, Hutchison R, Wasserburg GJ (1998) An isotopic and petrologic study of calcium-aluminum-rich inclusions from C03 meteorites. Geochim Cosmochim Acta 62(4) 689-714... 

Detailed experimental studies on rock-forming minerals (see Chakraborty and Ganguly, 1991, and references therein) have shown that the pressure effect on elemental diffusivity cannot be neglected in petrologic studies, in which highly variable pressure regimes are commonly involved. 

Table 4.9 gives a summary of diffusion data for divalent cations in aluminous garnets, with the relative activation volume. Although estimation of activation volume is still largely uncertain, its evaluation is essential when dealing with the wide baric regimes encountered in petrologic studies. As shown in the third column of table 4.9, the presence of AF implies substantial modifications of Qj on the kbar scale of pressure. 

Tin K and P in kbar) however, its application to other thermobaric conditions is not so appropriate. The most satisfactory formulations for the exchange reaction 5.216 are those of Slavinskiy (1976), Ganguly (1979), Saxena (1979), and Dahl (1980), which are based on a large body of thermodynamic data, petrologic studies, and natural observations. 

Previous geological work is scarce. The San Miguel skarn was discovered by Villar Fabre (1956). During the sixties, Villar Fabre Quartino (1966), and Quartino Villar Fabre (1967) conducted petrological studies of this deposit, defining skarn mineral facies. 

Maxwell, J., "Petrologic Studies, Buddington Volume, The Geological Society of America, Baltimore, 1962. 

Frezzotti ML, Peccerillo A (2004) Fluid inclusion and petrological studies elucidate reconstruction of magma conduits. Eos 85 157-163... 

Bartholome, P., 1962. Iron-magnesium ratio in associated pyroxenes and olivines. Geol. Soc. Am., Petrologic Studies A volume in honour of A.F. Buddington, New York, pp. 1-20. 

Benedix G. K., McCoy T. J., Keil K., and Love S. G. (2000) A petrologic study of the LAB iron meteorites constraints on the formation of the lAB-winonaite parent body. Meteorit. Planet. Set 35, 1127-1141. 

Ikeda Y. and Prinz M. (1993) Petrologic study of the Belgica 7904 carbonaceous chondrite hydrous alteration, thermal metamorphism, and relationship to CM and Cl chondrites. Geochim. Cosmochim. Acta 57, 439-452. 

The chemical fractionations observed among chondrites and the compositions of many chondritic components are best understood in terms of quenched equilibrium between phases in a nebula of solar composition (Palme, 2001 Chapters 1.03 and 1.15). The equilibrium model assumes that minerals condensed from, or equilibrated with, a homogeneous solar nebula at diverse temperatures. Isotopic variations among chondrites and their components show that this assumption is not correct and detailed petrologic studies have identified relatively few chondritic components that resemble equilibrium nebular products. Nevertheless, the equilibrium model is invaluable for understanding the chemical composition of chondrites and their components as the solar nebular signature is etched deeply into the chemistry and mineralogy. 

Hess H. H. (1962) History of ocean basins. In Petrologic Studies a Volume in Honor of A. F. Buddington... 

Danyushevsky E. V., McNeill A. W., and Sobolev A. V. (2002) Experimental and petrological studies of melt inclusions in phenocrysts from mantle-derived magmas an overview of techniques, advantages and complications. Chem. Geol. 183, 5-24. 

Numerous petrological studies have established that the protoliths of eclogites underwent progressive dehydration during prograde metamorphism, and that many were later rehydrated to... 

As discussed by Coogan et al. (2002), there are currently two classes of models for the formation of the gabbroic sequence that are, to first order, consistent with available constraints from marine seismic investigations, and structural and petrologic studies of gabbros in ophiolites and oceanic drill cores. In the first class of models (Figure 25(a)), crystallization occurs... 

Stuckless J. S., Bunker C. M., Bush C. A., Doering W. P., and Scott J. H. (1977) Geochemical and petrological studies of uraniferous granite from Granite Mountains, Wyoming. US Geol. Surv. J. Res. 5, 61-81. 

H.D. Holland, Petrologic Studies - A Volume to Honor A. F. Buddington, Geological Society of America, Colorado, p. 447,1962. 

Tsuya, H. (1955). Geological and petrological studies of volcano Fuji. Tokyo Daigaku Jishin Kenkyusho Iho 33, 341-382. 

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