Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (4) Citing Articles via Google Scholar Google Scholar Articles by Simmons, Wm. B. S. Articles by Webber, K. L. Search for Related Content GeoRef GeoRef Citation

Pegmatite genesis: state of the art

Department of Earth and Environmental Sciences, University of New Orleans, New Orleans, LA 70148, USA

^* Corresponding author, e-mail: wsimmons{at}uno.edu

No one universally accepted model of pegmatite genesis has yet emerged that satisfactorily explains all the diverse features of granitic pegmatites. Genesis from residual melts derived from the crystallization of granitic plutons is favoured by most researchers. Incompatible components, fluxes, volatiles and rare elements, are enriched in the residual melts. The presence of fluxes and volatiles, which lower the crystallization temperature, decrease nucleation rates, melt polymerization and viscosity, and increase diffusion rates and solubility, are considered to be critical to the development of large crystals. A number of new concepts have shed light on problems related to pegmatite genesis.

Cooling rates calculated from thermal cooling models demonstrate that shallow-level pegmatites cool radically more rapidly than previously believed. Rapid cooling rates for pegmatites represent a quantum shift from the widely held view that the large crystals found in pegmatites are the result of very slow rates of cooling and crystal growth.

Experimental and field evidence both suggest that undercooling and disequilibrium crystallization dominate pegmatite crystallization. London’s constitutional zone refining model of pegmatite evolution involves disequilibrium crystallization from an undercooled, flux-bearing granitic melt. The melt is not necessarily flux–rich and the model does not require the presence of an aqueous vapor phase.

Experimental studies of volatile- and flux-rich melts and fluid inclusion studies suggest that volatile-rich silicate melts may persist to temperatures well below 500 °C and even down to 350 °C.

Studies of melt inclusions and fluid inclusions have led some researchers to suggest that the role of immiscible fluids must be considered in any model regarding pegmatite genesis. Fluid saturation is thought to occur early in the crystallization history of pegmatites. Two types of melt inclusions along with primary fluid inclusions have been found coexisting in pegmatite minerals.

Advances by Petr ern in pegmatite classification are in wide use and the fractionation trends of Nb, Ta and other HFSE and K, Rb, Cs, Li, Ga and Tl are now well understood.

How pegmatitic melts are produced, the types of source rocks involved and how melt generation relates to plate tectonic models are challenging areas for future investigations. Also, the roles of regional zoning, anatexis, and chemical quenching in pegmatite genesis are areas for future pegmatite research.

Key-words: pegmatite, pegmatite genesis, thermal modelling, chemical quench, classification, regional zoning.

This article has been cited by other articles:

				M.-L. C. Sirbescu, M. A. Leatherman, J. J. Student, and A. R. Beehr APATITE TEXTURES AND COMPOSITIONS AS RECORDS OF CRYSTALLIZATION PROCESSES IN THE ANIMIKIE RED ACE PEGMATITE DIKE, WISCONSIN, USA Can Mineral, August 1, 2009; 47(4): 725 - 743. [Abstract] [Full Text] [PDF]

				D. R. Soares, H. Beurlen, S. d. B. Barreto, M. R. R. Da Silva, and A. C. M. Ferreira COMPOSITIONAL VARIATION OF TOURMALINE-GROUP MINERALS IN THE BORBOREMA PEGMATITE PROVINCE, NORTHEASTERN BRAZIL Can Mineral, October 1, 2008; 46(5): 1097 - 1116. [Abstract] [Full Text] [PDF]