Abstract

Rb–Sr and K–Ar age measurements for whole-rock and mineral samples representing the various rock units of the White Creek batholith and the adjacent Precambrian country rocks are reported. Four geological events have been identified: (1) emplacement and (or) consolidation of the marginal zones of the batholith at, or subsequent to, 126 m.y.; (2) final consolidation of the leucocratic quartz monzonite core rocks at 111 ± 5 m.y.; (3) a period of thermal activity affecting all batholithic rocks at 85 m.y.; and finally (4) a second thermal event affecting all batholithic rocks and resulting in partial, localized redistribution of radiogenic argon and strontium at 65 m.y.The leucocratic quartz monzonite core rocks are characterized by a high initial 87Sr/86Sr ratio of 0.7250 in marked contrast to the lower average value of 0.7077 determined for the boundary rock units of the batholith.Chemical and mineralogical data for the whole-rock samples exhibit gradational trends between all rock units of the batholith, indicating they have developed as a consequence of the differentiation of a homogeneous source magma. However, evidence provided by isotopic and trace-element studies suggests that the leucocratic quartz monzonite core rocks were derived from a separate source, and were emplaced during an unique intrusive event late in the cycle of plutonic activity.

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