Abstract
Abstract Jabal Tays trondhjemite and granophyre are leucocratic acidic rocks that intrude the melange zone of an ophiolitic complex. They consist of two small stocks 200 m in diameter and some dikes and vein-like bodies. Petrographically, they are medium—fine grained hypidiomorphic granular rocks consisting mainly of plagioclase (An10–60) and quartz which commonly shows myrmekitic texture. The mafic minerals are primarily biotite and muscovite, with occasional sericite, chlorite and epidote pseudomorphs after hornblende. The bulk chemical composition and trace elements are similar to trondhjemites from other ophiolite complexes. They also show calc-alkaline affinity. The K/Rb, Rb/Sr, and initial 87Sr/86Sr ( 0.7030 ± 0001 ) ratios, as well as the depletion of the (LIL) elements suggest an origin by partial melting of basic parent material in an island-arc tectonic setting over a subduction zone. The granophyres probably evolved from the trondhjemites either by crystal fractionation or crustal contamination. The whole-rock RbSr isochron age of 620 ± 40 Ma places an upper limit on the geologic and tectonic evolution of the Jabal Tays ophiolitic complex.
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