A possible link between gabbros bearing High Temperature Iddingsite alteration and huge pegmatoid intrusions: The Society Islands, French Polynesia

摘要: This paper reports new field observations and petrological, textural geochemical data on two gabbroic intrusions one pegmatoid dyke from the French Polynesian islands Maupiti Bora Bora, respectively. Olivine crystals Faataufi Barque de Hiro gabbros (Maupiti) include High Temperature Iddingsite (HTI), exhibiting three distinct morphological facies. Chemical crystallographical performed by electron microprobe, scanning microscope, X-ray diffractometry Near InfraRed spectroscopy show that HTI results modifications of olivine structure through intense hydroxylation Fe-oxidation. The HTI-free 120 m-wide Cloche (Bora Bora) exhibits a zonation heterogranular/intergranular gabbro (peripheral part) to typical (inner area). We propose tetrahedral classificatory diagram which can be used clearly distinguish characteristics pegmatoids those other coarse-grained samples. Through comparison with lava flow containing vesicle-rich segregation sheets, we suggest may correspond huge derived Maupiti-type HTI-bearing vapor-differentiation process. Both might considered as representative superposed levels in vertically arranged magmatic complex. In this view, bodies would represent lower part postulated system. Under high oxygen fugacity, have undergone important their structure, leading HTI. upper After expulsion solidification zone build-up gas pressure, residual melt gathered into shallow level crystallized there body.