Late Triassic–Early Jurassic I-type leucogranites and quartz diorites from the Kaçkar Batholith (Eastern Pontides, NE Türkiye): Implications for the generation of highly evolved felsic magmas at convergent plate boundaries

Eyüboğlu Y.

LITHOS AN INTERNATIONAL JOURNAL OF MINERALOGY, PETROLOGY, AND GEOCHEMISTRY, cilt.540541, ss.1-21, 2026 (SCI-Expanded, Scopus)

Özet

This study examines Late Triassic–Early Jurassic I-type leucogranites and quartz diorites from the Kaçkar Batholith (NE Türkiye) to constrain the origin of highly evolved felsic magmas at convergent plate boundaries. Zircon Usingle bondPb ages indicate crystallization of the Yedigöl quartz diorites and Sırakonaklar leucogranites at ∼210–207 Ma, whereas the Altıparmak leucogranites record a younger felsic event at ∼192 Ma, documenting episodic magmatism across the Triassic–Jurassic transition. The quartz diorites are calc-alkaline and metaluminous, displaying positive zircon Ce anomalies without Eu depletion, consistent with oxidized, hydrous, mantle-influenced magmas and limited plagioclase fractionation. In contrast, the leucogranites are evolved, weakly peraluminous, and characterized by very low Sr contents and pronounced negative Eu anomalies in both whole-rock and zircon chemistry, reflecting strong feldspar-controlled internal differentiation. The leucogranites include perthite- and antiperthite-bearing varieties, recording contrasting Ksingle bondNa feldspar systematics during magma evolution. All lithologies display mantle-influenced Sr–Nd–Pb and zircon Lusingle bondHf isotopic signatures consistent with an I-type, juvenile-dominated origin, excluding derivation from metasedimentary sources. Geochemical constraints indicate that the leucogranites did not form through simple fractional crystallization of quartz diorite magmas, but instead originated from feldspar-retentive partial melting of meta-igneous lower crust, driven by sustained thermal input from mantle-influenced magmatism within a vertically coupled arc system and followed by feldspar-dominated differentiation. Enrichment in Nb, Ta, Th, and U reflects magmatic fertility and late-stage accessory mineral concentration rather than economically significant rare-metal mineralization. Overall, the results highlight episodic felsic magma generation above a south-dipping subduction zone during Late Triassic–Early Jurassic.