Granite petrogenesis and the δ44Ca of continental crust

Stable Ca isotopes are an increasingly useful tool for understanding the sources and processes leading to formation of magmatic rocks, yet isotope fractionation during genesis silicic continental crust is still poorly understood. Here, we present Ca, Sr, Nd isotope, as well major- trace-element whole-rock geochemical data A-, I-, S-type granites (n = 30) from Australia/Tasmania, Canada, France (δ44CaBSE -0.6‰ +0.2‰) compare them phase-equilibrium models partial-melting (pelite, greywacke, MORB, enriched Archean tholeiite) crystallization (hydrous arc basalt, A-type granite) that incorporate novel ab-initio predictions in epidote K-feldspar. The calculations predict has similar δ44Ca anorthite K-feldspar isotopically lightest known silicate mineral at equilibrium (Δ44Cakspar-melt -0.4‰ 1000 K). Our model results suggest variations all three granite types can be fully explained through processes, without necessarily requiring addition exotic components (e.g., carbonate sediments). Heavy enrichments Lachlan Fold Belt, however, require isotopic disequilibrium between plagioclase melt, which use constrain average growth rates these systems. This also serves illustrate measurements used estimate crystal rates, even absence analyzable phenocrysts. In general, low diffusivities strong diffusivity ratios (D44/D40) low-H2O granitic magmas should lead resolvable effects plagioclase, relatively slow > 0.03 cm/yr). Combining our with those previous studies, demonstrate granitoids upper (with newly estimated δ44CaBSE -0.25 ± 0.02‰, 2SE) have compared basalts oceanic crust. Given pressure a major influence on across models, this implies melts feeding crustal dominantly evolve lower (10-14 kbar, either or fractional crystallization). observation suggests heavier preferentially recycled back into mantle subduction and/or lower-crustal delamination events, but unlikely had significant evolution geologic time.