Abstract:
The most complete and the largest ophiolitic outcrop of Pakistan the Bela ophiolite contains a wide range of leucocratic rock types. These include leucogabbro, basic pegmatite, diorite, quartz diorite, trondhjemite, epidote trondhjemite, granite, keratophyre and acidic pegmatite. The plagiogranite forms large outcrops as well as small dykes and lensoid bodies. In places, the acidic rock occurs interdigitating with the surrounding diabase. At a few locations, the acidic melt has intruded diorite. The characteristic very low potash and high soda-containing acidic plagiogranite is accompained by granitic rocks with higher potash content. Radiogenic isotopic measurements on samples from both potassic and sodic types are distinct and related to their separate tectonic environments. U-Pb isotopic measurements on zircons separated from the acidic plagiogranite samples yield a crystallization age of 651 Ma for both sodic and potassic samples. The sodic plagiogranites could have been derived from basic magma by fractional crystallization. The potassic granitic rocks may have been generated by crustal anatexis in the subduction zone by the residual heat of the ophiolite. On the bais of geochemical data a suprasubduction zone origin with partial marginal basin environment is proposed for the Bela ophiolite.
Page(s):
9-24
DOI:
DOI not available
Published:
Journal: Acta mineralogica pakistanica, Volume: 5, Issue: , Year: 1991