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Textural and Chemical Evolution of Unidirectional Solidification Textures in Highly Differentiated Granitic Rocks at K haraatyagaan, Central M ongolia
Author(s) -
Erdenebayar Jamsran,
Ogata Takeyuki,
Imai Akira,
Sereenen Jargalan
Publication year - 2014
Publication title -
resource geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 43
eISSN - 1751-3928
pISSN - 1344-1698
DOI - 10.1111/rge.12050
Subject(s) - quartz , geology , phenocryst , mineralogy , magma , geochemistry , crystallization , texture (cosmology) , scanning electron microscope , plagioclase , materials science , composite material , chemistry , paleontology , organic chemistry , volcano , artificial intelligence , computer science , image (mathematics)
Unidirectional solidification texture ( UST ) in an aplite body is recognized in the Neoproterozoic highly differentiated granitic rocks at K haraatyagaan, central M ongolia. On the basis of crystal morphology, two main types of UST were identified in the aplite body: (i) thin crenulate UST layers; and (ii) thick intergrowth UST layers. Bulk geochemistry indicates that the K haraatyagaan UST ‐bearing aplite and aplite dike are alkaline, and are enriched in light rare‐earth elements. Scanning electron microscopy and cathadoluminescence imaging of UST quartz from K haraatyagaan show four types of quartz: euhedral quartz phenocrysts with well‐developed concentric growth zoning ( Qa1 ) in the aplite; euhedral quartz with weak growth zoning in the aplite ( Qa2 ); UST quartz exhibiting distinct growth zones ( Qu1 ); and UST quartz showing mosaic texture ( Qu2 ). Crystallization temperatures determined by the T i‐in‐quartz geothermometer of Qa1 and Qu1 quartz range between around 500° C and 780° C and Qa2 and Qu2 range between about 490° and 630° C . The cathodoluminescence textures of quartz are predominantly caused by variations in the trace elements contents of quartz. The Qa1 and Qu1 quartz crystals are characterized by high T i and A l concentrations in the quartz lattice, and are observed in the bottom of the K haraatyagaan hill, which formed in the early, less evolved magmatic stage. The Qa2 and Qu2 UST quartz characterized by low T i and variable A l concentrations are found at the top. The UST layers crystallized along the upper part of the magma chamber in the presence of fluid phases exsolved from felsic magma.