Growth of upper plate lithosphere controls tempo of arc magmatism: Constraints from Al-diffusion kinetics and coupled Lu-Hf and Sm-Nd chronology

Continental crust formation at arcs, the arclogite “delamination” cycle, and one origin for fertile melting anomalies in the mantle

“…The tendency to founder is controlled by the competing effects of negative buoyancy forces (associated with compositional and thermal densification and the thickness of the cumulate layer) and viscous resisting forces. Thermobarometry of Sierran garnet pyroxenites indicates that prior to their hypothesized removal in the Pliocene, they last equilibrated at temperatures below *800°C at *50 km depth [11,43,[63][64][65][66]. This suggests that, following the formation of the cumulate layer, considerable cooling took place, most likely due to impingement upon the cold subducting Farallon plate as the arc root thickened [66].…”

“…In the case of cratonic lithosphere, the lithospheric mantle could be *200 km thick, whereas the lower crust is less than 20 km thick. In the case of arc lithosphere, it seems likely that the lithospheric mantle is thin, given that mature volcanic arcs may have crustal roots extending down to depths in excess of 60 km [11,21,29,30,[64][65][66]. Additionally, in juvenile or island arcs, thermobarometric constraints on the origin of basaltic magmas suggest the presence of hot asthenospheric mantle at depths shallower than 60 km [83,84], leaving little room for lithospheric mantle when typical arc crusts are *20-30 km thick.…”

“…Thermobarometry of Sierran garnet pyroxenites indicates that prior to their hypothesized removal in the Pliocene, they last equilibrated at temperatures below *800°C at *50 km depth [11,43,[63][64][65][66]. This suggests that, following the formation of the cumulate layer, considerable cooling took place, most likely due to impingement upon the cold subducting Farallon plate as the arc root thickened [66]. Using a diabase rheology as an analog for the rheology of garnet pyroxenite [67], we find that the effective viscosity at these temperatures is *10 22 Pa s (Table 1; Fig.…”

The rise and fall of continental arcs: Interplays between magmatism, uplift, weathering, and climate

“…What leads to long-lived magmatic flare-ups in continental arcs is unclear, but possibilities include changes in plate motion, lithospheric thinning by delamination/convective removal, and underthrusting of continental lithosphere in the back-arc region (Ducea and Barton, 2007). The eventual decline and termination of magmatism could be caused by thickening of the arc crust (e.g., by magmatism), which limits the extent of decompression melting in the asthenosphere (Chin et al, 2015;Karlstrom et al, 2014). For the purposes of this paper, we take the observed flareup as given.…”

Spatial and Depth‐Dependent Variations in Magma Volume Addition and Addition Rates to Continental Arcs: Application to Global CO2 Fluxes since 750 Ma

“…Total thickness of the arc crust has been estimated to be~80 km, based on calculations by and and~90 km by Chin et al (2015). The magmatic flare-up period lasted for~60 Ma from 140 to 80 Ma as the arc migrated eastward and was accompanied by syn-magmatic crustal deformation resulting in greater than~60% shortening in the main arc.…”