International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

ENCLAVES IN THE ROCHOVCE GRANITE INTRUSION AS INDICATORS OF THE TEMPERATURE AND ORIGIN OF THE MAGMA

Pages: 125 - 138

Authors: LUBOMIR HRASKO, ALEXANDER B. KOTOV, EKATHERINA B. SALNIKOVA, VICTOR P. KOVACH

Abstract: Two boreholes in the Mo-W-bearing porphyric Cretaceous granite, located near the village of Rochovce, Western Carpathians, reveal the existence of two types of enclaves: 1. micaceous enclaves (biotite-plagioclase gneisses without quartz, with highly calcitic plagioclases) and 2. mafic microgranular enclaves (MME), with predominantly dioritic composition. In the first type, corundum, Zn-hercynite and magnetite were produced due to the high temperature melting of biotite. These are considered to be restites. The melting reactions in biotite indicate that the granite magma temperatures exceeded 800 °C at the time of the enclave melting. The mafic microgranular enclaves represent portions of mafic magma incorporated in the granitic magma. Seven types of mineralogical-petrological indicators of magma mixing were found. The chemical and Sm/Nd isotopic characteristics of the host granite and MME show that chemical and isotopic equilibration was achieved within the granite-MME system. The initial ∈Nd value in granite (-3.0) indicates that some mafic magmatic material was added to the magma chamber. The apparent crustal residence age (T*DM = 1100 Ma) indicates an old, Precambrian history of the crustal source material. Thus, the Rochovce magma was derived from a crustal source, with addition of more mafic (probably mantle-derived) magma.

Keywords: Western Carpathians, Cretaceous, granite, mafic microgranular enclaves, micaceous enclaves, mixing, Sm/Nd isotopes

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