The incomplete crystal-melt separation of volcanic-plutonic complex in the southern Great Xing'an Range, NE China

Abstract

Probing the petrogenetic link between volcanic and plutonic rocks is crucial for deciphering continental crust evolution. Reconstructing the crystal-melt separation process represents a research frontier, albeit its role in silicic mushes remains contentious. Here, we present an integrated study of the Mangtudaba volcanic-plutonic complex from the southern Great Xing'an Range in NE China, comprising bulk-rock geochemistry and in situ zircon geochemical and geochronological analyses. All lithologies, including quartz monzonite, crystal-rich trachydacite, and crystal-poor rhyolite/rhyolitic tuff, exhibit consistency in spatial distribution, zircon ages (∼138 Ma), and Hf isotopic compositions [ε_Hf(t) = +4.7 − +9.0], demonstrating their derivation from a common magma reservoir. Both petrographic and geochemical characteristics reveal that quartz monzonites represent residual cumulates after the extraction of high-silica rhyolitic melts. Integrating microstructural evidence with terminal porosity measurements (Φ, quartz monzonites: 0.2–0.3; trachydacites: 0.1–0.2), we speculate that the crystal-melt separation in Mangtudaba complex was incomplete, leaving significant pore melt (F_trap, 10–35 vol%) trapped in cumulates and unexpected cumulate fragments entrained into the extracted melts. The trachydacites displaying cumulate signatures originated from mush rejuvenation and witnessed the interruption of efficient phase separation. Zircons display distinct texture-temperature-composition spectra that record their redistribution and recrystallization history in discrete melt domains, including extracted melts, trapped interstitial melts, and hot replenishments. Regarding the separation mechanisms, compaction played a dominant role, while magma recharge facilitates phase separation only within an optimal flux range, beyond which excessive replenishments become counterproductive. This study establishes a comprehensive, quantitative model of crystal-melt separation and advances our understanding of volcanic-plutonic connections.