Nyílt rendszerű magmás folyamatok: magmakeveredés, kristálycsere és kumulátum-recirkuláció nyomai a Ditrói alkáli masszívumban (Orotva, Románia)

The Tarniţa Complex represents the characteristic ultramafic and mafic rock assemblage of the northern part of the Ditrau Alkaline Massif, exposed in the Eastern Carpathians (Romania). The ~60 m2 surface of the artificial outcrop in the intrusive igneous rock is located in the western part of the complex, near the interflow of the Pietrariei de Sus and Jolotca creeks. It provides a unique insight into the mingling and mixing processes which occurred between magmas (a) in the former magma storage system and (b) during the incorporation of the earlier crystallized magmatic fragments entrained during the new magma intrusions. The host rock of the studied section (grey, medium– and coarse–grained diorite with an oriented texture) comprises four different types of mafic magmatic enclave (MME): (i) mafic enclave; (ii) feldsparaggregatic enclave; (iii) porphyritic (feldsparaggregatic), mafic enclave and (iv) ultramafic enclave. In addition, a felsic xenolith type of distinct origin is also present: some of the felsic diorite enclaves are hosted in mafic enclaves, thus suggesting they were transported by the recharging mafic magma into the magma chamber. The most important feature of the magma mingling process is the presence of fine-grained, lens-shaped, elongated mafic magmatic enclaves parallel with each other and with the orientation of the minerals in the host rock. The rock wall shows this typical magma mingling structure and implies that mafic recharge was a dominant process during the evolution of the magma storage system. The angular felsic xenoliths and ultramafic enclaves indicate the recycling of earlier cumulates by the intruding magmas. The mafic rim of the mafic magmatic enclaves and the nearby black bands (“schlieren”) represent additional important characteristics of the mingling structures.