Quick Search:    advanced search

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

This Article 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 Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Clarke, D. B. Articles by Erdmann, S. GeoRef GeoRef Citation

Is stoping a volumetrically significant pluton emplacement process?: Comment

D. Barrie Clarke^1, and Saskia Erdmann¹

¹ Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada

Correspondence: E-mail: clarke@dal.ca

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
Glazner and Bartley (2006) have challenged the "large-magma-body-emplaced-by-stoping" model for granite batholiths. Instead, primarily as a consequence of their geochronological data on the Tuolumne Batholith, Glazner and Bartley (2006), building on Glazner et al. (2004) and Coleman et al. (2004), have inferred that plutons grow by a prolonged sequence of magma injections and/or dikes. Such emplacement of magma by dikes, as opposed to emplacement of magma by stoping, is much less likely to produce xenoliths; therefore, the abundances of country-rock xenoliths in granites represent a major problem for the dike emplacement hypothesis, and require that Glazner and Bartley explain them in some other way. Thus, according to Glazner and Bartley (2006), such xenoliths are not stoped fragments of country rock because:

(1) they are in situ pieces of country rock isolated from their source by dikes;

(2) their particle-size distribution is inappropriate to have been derived by stoping; and

(3) the contamination of granite bodies, a logical consequence of stoping, does not occur to any significant degree.

Below, we take issue with these three assertions.

	ORIGIN OF XENOLITHS

 
When is a xenolith not a xenolith? The commonly accepted view of xenoliths, a subset of "enclaves," is that they are broken and/or spalled and/or stoped fragments detached from the country rocks and "entirely surrounded" (Didier and Barbarin, 1991) by the host magma. Most workers would go on to accept that the fate of such "free-swimming" xenoliths, including their spatial coordinates, sizes, shapes, mineral assemblages, textures, and bulk compositions, are subject to whatever degree of physical and chemical equilibrium they can establish with the magma before all such activity ceases (e.g., Green, 1994; McLeod and Sparks, 1998; Beard et al., 2005). In contrast, Glazner and Bartley (2006) claim that these foreign blocks are in situ pieces carved . . . [Full Text of this Article]