Predicting Rates and Distribution of Carbonate Melting in Oceanic Upper Mantle: Implications for Seismic Structure and Global Carbon Cycling

Abstract

Coupling a global mantle flow model with a parameterized carbonate solidus, we examine the global distribution and extent of carbonate melting beneath the ocean basins. We predict carbonate melting in spatially heterogeneous patterns throughout the oceans. The rate of CO2 segregation from the mantle by off‐axis carbonate melting (~1.1 × 1012 mol/year) is comparable to the global ridge flux (~1.2 × 1012 mol/year). As the generation of carbonate melts should be enhanced in regions of mantle upwelling, we compare upwelling patterns with seismic detections of the G‐discontinuity. The upwelling velocities in areas where the G‐discontinuity is detected are not statistically different from areas with no detections—implying that the generation and pooling of carbonate melts are not dominant mechanisms in forming the G‐discontinuity. However, detections of a deeper seismic discontinuity are correlated with enhanced upwelling velocities, suggesting locally higher melt fractions at the transition between carbonate‐only and carbonate‐enhanced silicate melting.

Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds

“…Carbonate can also be found in the peridotite portion of the oceanic lithosphere, especially in samples emplaced at fracture zones (Li et al., 2019). Abyssal peridotite at the ridge carries organic carbon (Ménez et al., 2018) that is likely augmented by the ambient flux of CO 2 to the base of the lithosphere as it ages in the ocean basins (e.g., Clerc et al., 2018). Thus both the oceanic crust and mantle portion of the lithosphere can contain significant carbon.…”

High-pressure elastic properties of dolomite melt supporting carbonate-induced melting in deep upper mantle

“…The small amount (<0.1%) of melt produced by melting of carbonated peridotite ( 1 ), or by redox melting of upwelling reduced carbon-enriched mantle ( 9 ) is likely to be carbonatite (with ∼40 wt% CO 2 ) at a depth greater than ∼300 km or carbonate-rich silicate melt (≤ 25 wt% CO 2 and ≥25 wt% SiO 2 ) at a shallower depth. Geodynamic modeling on the rates and distribution of carbonate melting using mantle upwelling patterns also shows that low-degree carbonate-induced melting occurs pervasively throughout the oceanic upper mantle at depths greater than ∼150 km ( 51 ). The presence of such carbonate-rich melt at greater depths (∼150–330 km) than typical silicate melting (less than ∼85 km deep) may well explain the observed deeper geophysical anomalies in the upper mantle ( 52 – 55 ), implying that carbonated incipient melting may extend to as deep as ∼300–330 km.…”

A comparison of oceanic and continental mantle lithosphere

“…However, the association of upwelling asthenosphere, melt generation, and converted/reflected detections of the LAB remains unclear. Clerc et al (2018) did not find a significant correlation between upwelling velocities in a global flow model and the Schmerr (2012) SS precursor LAB detections from depths less than 80 km, and did not resolve a correlation when the SS precursor results of Tharimena et al (2017a) were considered. However, Clerc et al (2018) point out that convection at scales smaller than resolved in their flow model may be an alternative source of partial melt.…”