Petrography and Chemistry of the Younger Granitic Intrusives, Llano Uplift, Central Texas




Campos, Juan Marcel

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Younger Intrusives from the Llano Uplift in central Texas reveal geochemical source diversity that reached a heterogeneously differentiate granitoid type (granodiorites to granites) and pockets of partial anatectic melts. Proposed magmatism shows a lower crustal igneous subduction signature with metasedimentaries and metamorphic schists and gneisses melted by crustal relaxation from uplift following orogenesis of the Grenville Mountains in the Proterozoic Eon. Plutons of the Keese and Enchanted Rock vary significantly compared to the rest of the Younger Intrusives which indicated batch crystallization with antecedent dehydrational partial melting as a foregoing magmatic process shown by trace element modeling and petrographic investigations. A comparison to the eastern Town Mountain Granites found fluid migration compatibilities but variances in major constituents and magma type (considered I-Type in the Younger Intrusives and undetermined A-Type signature for the Town Mountain Granites). The Restite Unmixing Model (proposed by A. JR White and B.W. Chappell) contrast appropriately with the Younger Intrusives due to source differences (unmixing), I-Type signatures, anatectic melts, and extensive geochemical suite variations for such highly differentiation rocks. Therefore, decompressional relaxation occurred gradual to allow transfer melting at lower crustal regions from upper crustal regions, which can deliberate the age of the Younger Granitic Intrusives.


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Llano Uplift, Petrology, Texas, Town Mountain, Younger Intrusives