Magmatic evolution of a Cordilleran flare-up and its role in the creation of silicic crust

Abstract

The role of magmatic processes as a significant mechanism for the generation of voluminous silicic crust and the development of Cordilleran plateaus remains a lingering question in part because of the inherent difficulty in quantifying plutonic volumes. Despite this difficulty, a growing body of independently measured plutonic-to-volcanic ratios suggests the volume of plutonic material in the crust related to Cordilleran magmatic systems is much larger than is previously expected. To better examine the role of crustal magmatic processes and its relationship to erupted material in Cordilleran systems, we present a continuous high-resolution crustal seismic velocity model for an ~800 km section of the active South American Cordillera (Puna Plateau). Although the plutonic-to-volcanic ratios we estimate vary along the length of the Puna Plateau, all ratios are larger than those previously reported (~30:1 compared to 5:1) implying that a significant volume of intermediate to silicic plutonic material is generated in the crust of the central South American Cordillera. Furthermore, as Cordilleran-type margins have been common since the onset of modern plate tectonics, our findings suggest that similar processes may have played a significant role in generating and/or modifying large volumes of continental crust, as observed in the continents today.

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

“…In general, estimates of CO 2 fluxes from arc volcanoes based on direct measurements of gas concentrations and flux calculations are higher (e.g., 18-43 Mt C/year) compared to estimates of diffusive outgassing in arcs (e.g., 4-12 Mt C/year; Kelemen & Manning, 2015). Although the latter is difficult to constrain, these estimates are surprising given the large plutonic to volcanic ratio observed (e.g., Ward et al, 2017; Table 1). However, assuming that these estimates are reasonable, one explanation could be that arc volcanoes source the underlying magma plumbing systems at several crustal levels and thus channelize CO 2 from magma chambers to the surface.…”

“…Based on recent publications (e.g., Ward et al, 2017), volcanic additions are thought to be less than 10% of the plutonic additions. Based on recent publications (e.g., Ward et al, 2017), volcanic additions are thought to be less than 10% of the plutonic additions.…”

“…Where volcanic units are exposed in isolated pendants, local stratigraphic correlations between pendants are used to infer predeformation lateral extents. Based on recent publications (e.g., Ward et al, 2017), volcanic additions are thought to be less than 10% of the plutonic additions. Thus, we are generous with our volcanic estimates in an attempt to avoid underestimating the volcanic additions.…”

“…Less well studied is the contribution of CO 2 from magmas stalled and crystallized in the crust, which exsolve a volatile phase lost to the surface (i.e., diffusive outgassing). Plutonic footprints of arc systems are volumetrically enormous in comparison to volcanic caps, with plutonic to volcanic ratios ranging from 10:1 to 30:1 (Lipman & Bachmann, 2015;Tierney et al, 2016;Ward et al, 2017;Zandt et al, 2003). MARs calculated in this study include plutonic and volcanic rocks and thus allow the estimate of potential diffusive CO 2 outgassing and outgassing at volcanic centers associated with eruption.…”

“…Furthermore, in magma-rich arcs, the volume of magma added to the crust influences its rheology and mass balance causing crustal thickening and mountain building (e.g., . Plutonic footprints of arc systems are volumetrically enormous in comparison to volcanic caps, with plutonic to volcanic ratios ranging from 10:1 to 30:1 (Lipman & Bachmann, 2015;Tierney et al, 2016;Ward et al, 2017;Zandt et al, 2003). The release of CO 2 to the atmosphere through arc volcanoes plays a major role in the global carbon cycle (e.g., Kelemen & Manning, 2015), and its influence on modulating climate variability throughout Earth's history has been documented (e.g., McKenzie et al, 2016).…”