Abstract
Detailed study of the petrology of Pulau Ubin island in the southern Malay Peninsula has unravelled convincing evidence of the operation of magma mixing in the genesis of certain granitoids. Significant features exposed on Pulau Ubin include synplutonic dykes, enclave dykes and the important, newly discovered “globular rock”. These features, in particular the extremely enclave-rich globular rock, show microgranular enclaves, a class of enclaves now recognized world wide, to be agents of magma mixing. The microgranular enclave-granitoid association represents a stage in the mixing of magmas of contrasted composition arrested before completion. In this context microgranular enclaves represent quenched globules of basic magma within commingled, cooler granitoid magma. Enclave formation is a vital stage in the magma mixing process since it greatly increases the area of interface between the commingling magmas. The ultimate petrographic and chemical character of most microgranular enclaves is determined by solidified enclave-granitoid magma reaction superimposed on previous globule magma-granitoid magma hybridization.
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