Petrology, geochemistry and tectonic setting of intrusive massives of Baft ophiolitic – melange, Southeast of Kerman, Iran.

摘要

Baft ophiolitic – mélange belt is a part of the ophiolite melange belt of central Iran whose genesis is considered as an environment related to Tethys subduction at Upper Cretaceous. Major part of intrusive masses of Baft ophiolitic – melange form gabbros with the inequigranular texture fine to coarse and pegmatitic, plagiogranites also with inequigranular general texture have been developed within the isotropic gabbros as local small masses or vein and or these have been injected as relatively thick veins within the dolerite dikes. Plagiogranites are located mainly in the range of volcanic arc and syncollision, and gabbros are located in the range of calc alkaline arc basalts. Based on the REE distribution pattern normalized according to chondrite plagiogranites indicate relatively similar pattern with gradual changes in the concentration of REE that indicates these rocks is syngenetic. The LREE enrichment shows that granites are related to suprasubduction zone that originally has been formed from island arc tholeiitic series or calk–alkaline series. Relative enrichment with almost flat pattern especially in part HREE, can be related to the shallow depth of partial melting for magma production of these rocks and or participation of amphibole in their formation, therefore consideration of hornblende gabbro and or amphibolitic source rock seems more logical for at least plagiogranites that are specifically enriched in HREE. In gabbros also the REE pattern normalized based on chondrite follow trend almost flat along with an enrichment slight increase of LREE elements in comparison with HREE that is indicating similar origin of gabbroic samples. According to the existence of defined differences in the content and pattern of REE in most samples of plagiogranite and gabbros of Baft ophiolitic–mélange–acid phase derivation from the gabbros does not seem plausible at least in template of partial melting for most samples of plagiogranite. Since the content of REE in the Baft plagiogranites is not higher than gabbros and even in one of samples this amount is lower than gabbros level, therefore acid phase derivation is not also plausible for most samples in the template of fractionation process. However, due to the field interconnected part of plagiogranitic with the part of doleritic in Baft ophiolitic–mélange–it is possible that fractional crystallization of basic rocks doleritic that is accompanied with pyroxene and plagioclase separation be able to produce plagiogranitic magma with features of volcanic arc similar to that of what is seen in the Baft area.