Transition from Paleogene Normal Calc-Alkaline to Neogene Adakitic-Like Plutonism and Cu-Metallogeny in the Kerman Porphyry Copper Belt: Response to Neogene Crustal Thickening

Tertiary magmatic activities in the Kerman porphyry copper belt (KPCB) formed two contrasting episodes of granitoids: (1) Jebal Barez-type (late Eocene-early Miocene) associated with extensive calc-alkaline/shoshonitic volcanism but without and/or with only minor Cu-mineralization, and (2) Kuh Panj-type (middle Miocene-Pliocene) associated with major porphyry copper mineralization. Neogene granitoids exhibit high Sr (406-1015 ppm) and low Y ( < 18 ppm) contents, moderately high REE fractionation (La/Yb=19-53) and lack of negative Eu anomalies (Eu/Eu*?1) which is comparable with the adakitic-like magmas, when compared with Jebal Barez-type normal calc-alkaline granitoids (Sr=184-576 ppm; La/Yb < 14.7; Eu/Eu* < 1). The magmatic evolution from normal calc-alkaline in Paleogene to adakitic-like signature in Neogene which is reflected in an increase in REE fractionation can be interpreted by progressive increase in pressure and the availability of water at the lower crustal site of magma generation. These processes can be in response to crustal thickening related to excessive compressional tectonic regime during the late stages of arc development in a post-collisional tectonic setting. From the metallogenetic point of view, increasing the oxidizing conditions at the lower crustal site of melt generation due to the amphibole breakdown during Neogene crustal thickening and also declining of volcanism in this time were two critical determinants on development of porphyry copper metallogeny in Kerman region.