Study on formation process of layered MMEs based on field observation and petrographic characteristics: A case study from Taejongdae, Busan Korea.

Mafic Magmatic Enclaves (MME) are a common feature in granitic rocks. However, the Multi-layered MME developed in the outcrop of Cretaceous granite in Taejongdae National Geopark, Busan is a unique phenomenon providing useful information on the formation of MMEs. Multi-layered MME is defined here as MME composed of several contrasting rock shells. Characteristics and origin of MMEs have been studied by several ways; descriptively, geochemically and isotopically due to their importance in the evolution of igneous rocks. This study focuses on the understanding of the formation mechanism of the multi-layers and their rock type diversity. To achieve these goals, field observation between the MMEs and the host granite, petrographic studies and XRF analysis have been carried out. The results show that the MMEs have different shapes and sizes, ranging from elliptical to angular, and from a few centimeters to a meter, respectively. Based on the lithology and the number of layers, the studied MMEs are subdivided into three types as followed; a) single layer type, b) double layer type, and c) triple layer type. The single and double layer types have relatively angular shapes, and their contacts with the host granite are commonly sharp. Layer-forming rocks are variable from mafic porphyritic, mafic fine- to medium- and felsic coarse-grained. The triple layer type has a circular to elliptical shape, while its contact with the host granite is gradual indicating diffusion. It also shows gradual compositional change from mafic to felsic. It is interesting that some of the triple MMEs are injected by granitic materials through cracks. That may indicate brittle deformation during cooling process. The two internal layers of the triple layer MMEs have almost the same mineral composition with different textures indicating the result of cooling process. However, the outer dioritic layer shows mixing composition of mafic and felsic magma, and thus it may indicate that it was generated by the chemical transfer of elements with the host granite. The sharp contact with the host rock and relatively angular shape of the single and double layer types may indicate that they are formed by breaking of triple layer types before the crystallization of the host granite. To confirm these ideas, more petrographic and chemical analyses are necessary.