Basalt volatile fluctuations during continental rifting: An example from the Rio Grande Rift, USA

Abstract

Hydration and metasomatism of the lithospheric mantle potentially influences both the magmatic and tectonic evolution of southwestern North America. Prior studies have suggested that volatile enrichments to the mantle underlying western North America resulted from shallow subduction of the Farallon Plate during the Laramide . This study examines temporal and spatial variations in volatile elements (H 2 O, Cl, F, and S) determined from olivine and orthopyroxene-hosted melt inclusions along and across the Rio Grande Rift, the easternmost extent of Laramide shallow subduction. Maximum chlorine enrichments are observed in the southern rift with a Cl/Nb of $210 and reduce with time to MORB-OIB levels ($5-17). Measured water abundances are <0.8 wt % in rehomogenized inclusions; however, calculated H 2 O, based on Cl/Nb systematics, primarily varies from 0.5 to 2 wt % H 2 O. Sulfur abundances (<0.61 wt %), and calculated sulfide saturation, indicate magmas with high Cl/Nb also contain oxidized sulfur. The abundance of fluorine in melt inclusions (up to 0.2 wt %) is not correlated to other volatile elements. Temporal variations in melt inclusion volatile abundances coupled with varying isotopic (Sr-Nd-Pb) whole-rock systematics suggest a transition from lithospheric to asthenospheric melt generation in the southern RGR and potential lithosphere-asthenosphere melt mixing in the central RGR. East to west decrease in volatile enrichment likely reflects a combination of varying mantle sources and early removal of metasomatized lithospheric mantle underlying regional extension. Results indicate, from multiple causes, subduction-related volatile enrichment to the lithospheric mantle is ephemeral, and strong enrichments in volatiles are not preserved in active magmatic-tectonic provenances.

Shallow melting of MORB‐like mantle under hot continental lithosphere, Central Anatolia

“…Minimum melt water contents, averaging 1.0 wt %, were estimated by assuming primary melt H 2 O/Ce' 5 200, the average ratio for MORB and OIB [Michael, 1995;Dixon et al, 2002]. Similar H 2 O/Ce ratios have been measured or inferred for mafic melts in the southwestern U.S. (<450 and clustering at <250) [Gazel et al, 2012;Rowe et al, 2015;Plank and Forsyth, 2016], which, like Central Anatolia, represents a setting that experienced arc volcanism and subsequent slab rollback. Resulting maximum individual temperatures for Hasan Monogenetic Cluster basalts with >8 wt % MgO range from 1265 to 13358C, averaging 1300 6 198C (1 s.d.)…”

What lies beneath? Reconstructing the primitive magmas fueling voluminous silicic volcanism using olivine-hosted melt inclusions

“…MIs were homogenized through standard 1 atm heating experiments to remove postentrapment crystallization (Danyushevsky et al, 2002;Rowe et al, 2015). Rehomogenized MIs and olivine hosts were analyzed for major elements by electron microprobe (Table DR3), and then MIs >35 µm across were analyzed for trace-element concentrations by laser-ablation inductively coupled plasma-mass spectrometry (Table DR4).…”

“…Rehomogenized MIs and olivine hosts were analyzed for major elements by electron microprobe (Table DR3), and then MIs >35 µm across were analyzed for trace-element concentrations by laser-ablation inductively coupled plasma-mass spectrometry (Table DR4). Following analysis, measured glass compositions were corrected for over/underheating (Rowe et al, 2015) and olivine-melt postentrapment reequilibration (Fe loss) using Petrolog3 (Danyushevsky and Plechov, 2011). A fundamental assumption required for Fe-loss corrections is that the whole-rock Fe content is representative of the MIs prior to entrapment.…”

Sr and Nd isotopic compositions of individual olivine-hosted melt inclusions from Hawai'i and Samoa: Implications for the origin of isotopic heterogeneity in melt inclusions from OIB lavas

“…Thus, recycled materials in hotspot lavas are not expected to have high Cl/K (e.g., Kendrick et al, 2013) or Cl/Nb (Rowe and Lassiter, 2009), and mantle-derived lavas that have not assimilated seawater-derived materials have low Cl/Nb ratios (e.g. 5-17; Rowe et al, 2015;Michael and Cornell, 1998;Saal et al, 2002;Stroncik and Haase, 2004;Rowe and Lassiter, 2009).…”