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K-feldspar oscillatory zoning constraining efficient crystal fractionation in high-silica magma: A case study of the Dacaowu pluton, eastern China
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DOI：10.1016/j.gexplo.2026.108042.png)
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Abstract
En 中文
The efficiency and mechanisms of significant crystal fractionation in high-silica granitic magmas remain debated, largely due to their high viscosity, which strongly impedes crystal mobility and melt-crystal segregation. The Dacaowu granodiorite in northwest Jiaodong, eastern China, characterized by its high-silica composition and the presence of mafic enclaves, provides an ideal target for studying the above-mentioned issues. Integrating petrography, zircon U-Pb geochronology, mineral geochemistry, and whole-rock geochemistry, this study reveals the dynamic processes governing crystal fractionation in high-silica magmatic systems and deciphers the origin of K-feldspar overgrowth textures. LA-ICP-MS zircon U-Pb dating yields a weighted mean age of 126.8 +/- 1.2 Ma. Whole-rock geochemistry indicates high-K calc-alkaline, metaluminous (SiO2 = 72.32-75.36 wt%, A/CNK = 0.97-0.99), with an adakitic affinity (Sr = 648-814 ppm, Y = 5.9-10.9 ppm, Sr/Y = 60.18-138.67, (La/Yb)N = 28.96-105.45) and a weak negative Eu anomaly (delta Eu = 0.86-0.95). Amphibole thermobarometry (861-888 degrees C; 246-308 MPa) and biotite thermobarometry (570-690 degrees C; 107-152 MPa) reveal a continuous evolutionary process. K-feldspar compositional profiles show potassium-rich cores (Ab = 7.18) and rhythmically zoned sodium-rich rims (Ab = 96.01). These oscillatory zones provide direct evidence of multiple mantle-derived melt injections. Multiple injections of mantle-derived melts acted as the key driver of compositional oscillation and efficient crystal fractionation in this high-silica magma. These recharge events supplied heat, triggered cyclic K/ Na variations, and induced convective shear, thereby counteracting the high viscosity of the melt, sustaining prolonged K-feldspar growth, and enhancing effective melt-crystal segregation. Combined with the temporal and spatial relationship with gold deposits, the above processes may be related to the gold mineralization in Jiaodong Peninsula.
Keywords:
K -feldspar phenocrysts
Mafic enclaves
Magma mixing
Crust-mantle interaction
K -feldspar overgrowth
Jiaodong Peninsula
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