Abstract

Studies of pretectonic plutons in the Foothills terrane, central Sierra Nevada, California, along with a review of studies on syntectonic and post-tectonic plutons, indicate that no single criterion can establish the relative timing of pluton emplacement and regional deformation. Criteria most often used are whether a pluton is deformed, cuts regional structures, or is associated with porphyroblasts that postdate regional structures. However, all three types of plutons may (1) appear deformed or nondeformed, (2) have contacts that appear to cut structures in the wall rocks, and (3) have porphyroblasts in their aureoles that display varied timing relations. The ambiguity of these criteria emphasize the need for careful studies of the structures present throughout the pluton and surrounding wall rock, with particular attention paid to regions where the pluton contact is at high angles to regional structures. Porphyroblast-cleavage relations are an important tool in this regard, but also must be used with caution.

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