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Petrographic characteristics of the appinite-granodiorite intrusion, eastern Drava depression (Eastern Croatia)

The appinite-granodiorite shallow intrusive body is characterized by complex textural relationships between different types of rocks. The shallower part of the hypabyssal body is composed mainly of granodiorite with hornblende diabase enclaves, while the deeper part is made up of intermediate lithology – monzodiorite. The monzodiorite is characterized by a fine-grained, hypidimorphic granular, locally porphyritic and poikilitic textures. It is composed of plagioclase, hornblende, orthoclase, quartz, biotite, accessory opaques, apatite and zircon. The hornblende diabase is porphyritic with phenocrysts of plagioclase and hornblende set in a finer groundmass composed of plagioclase, hornblende, accessory opaques, apatite and zircon, while biotite, quartz and orthoclase are situated near the contact with the granodiorite. The granodiorite exhibits a seriate texture and is composed of plagioclase, quartz, orthoclase and biotite, with accessory opaques, apatite and zircon. Hornblende occurs near the contact with the hornblende diabase. Enclaves in the shallow part are ~1-10 cm long and are very diverse, having different shapes and contact sharpness with the host rock. Angular enclaves with sharp contacts with host rocks indicate intrusion of mafic magma at an advanced stage of crystallization, while ellipsoid enclaves with sharp contacts point to intrusion of liquid mafic magma. Ameboid-shaped enclaves with diffuse contacts are characterized by the occurrence of a hybrid lithology and indicate low temperatures and viscosity gradients between the mafic and felsic end members. The different types of enclaves point to complex and long-term processes involving the interplay of the two end-member magmas. The monzodiorite in the deeper parts of the body most likely represents a hybrid lithology. Textural characteristics of this rock, such as the occurrence of sieve-textured plagioclase and acicular apatite point to dynamic setting and unsteady conditions in magma chamber. The lower liquidus temperature of the water-rich mafic magma probably enhanced the process of mixing between hot mafic and colder felsic end members. Mixing processes dominated the deeper part of the chamber, while in the shallower part mingling processes prevailed.

hornblende diabase, monzodiorite, granodiorite, magma mixing, magma mingling

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