We investigated the state of the arc background mantle (i.e. mantle wedge without slab component) by means of olivine CaO and its Cr-spinel inclusions in a series of high-Mg# volcanic rocks from the Quaternary Trans-Mexican Volcanic Belt. Olivine CaO was paired with the Cr# [molar Cr/(Cr + Al) *100] of Cr-spinel inclusions, and 337 olivine+Cr-spinel pairs were obtained from 33 calc-alkaline, high-K and OIB-type arc front volcanic rocks, and three monogenetic rear-arc basalts that lack subduction signatures. Olivine+Cr-spinels display coherent elemental and He–O isotopic systematics that contrast with the compositional diversity of the bulk rocks. All arc front olivines have low CaO (0.135 ± 0.029 wt %) relative to rear-arc olivines which have the higher CaO (0.248 ± 0.028 wt %) of olivines from mid-ocean ridge basalts. Olivine 3He/4He–δ18O isotope systematics confirm that the olivine+Cr-spinels are not, or negligibly, affected by crustal basement contamination, and thus preserve compositional characteristics of primary arc magmas. Variations in melt H2O contents in the arc front series and the decoupling of olivine CaO and Ni are inconsistent with controls on the olivine CaO by melt water and/or secondary mantle pyroxenites. Instead, we propose that low olivine CaO reflects the typical low melt CaO of high-Mg# arc magmas erupting through thick crust. We interpret the inverse correlation of olivine CaO and Cr-spinel Cr# over a broad range of Cr# (~10–70) as co-variations of CaO, Al and Cr of their (near) primary host melts, which derived from a mantle that has been variably depleted by slab-flux driven serial melt extraction. Our results obviate the need for advecting depleted residual mantle from rear- and back-arc region, but do not upset the larger underlying global variations of melt CaO high-Mg# arc magmas worldwide, despite leading to considerable regional variations of melt CaO at the arc front of the Trans-Mexican Volcanic Belt.
- Award ID(s):
- 1714892
- NSF-PAR ID:
- 10354652
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Subduction‐related lavas have higher Fe3+/∑Fe than midocean ridge basalts (MORB). Hypotheses for this offset include imprint from subducting slabs and differentiation in thickened crust. These ideas are readily tested through examination of the time‐dependent evolution of slab‐derived signatures, thickening crust of the overriding plate, and evolving redox during subduction initiation. Here, we present Fe3+/ΣFe and volatile element abundances of volcanic glasses recovered from International Ocean Discovery Program (IODP) Expedition 352 to the Izu‐Bonin‐Mariana (IBM) forearc. The samples include forearc basalts (FAB) that are stratigraphically overlain by low‐ and high‐silica boninite lavas. The FAB glasses have 0.18–0.85 wt% H2O, 75–233 ppm CO2, S contents controlled by saturation with a sulfide phase (602–1,386 ppm), Ba/La from 3.9‐10, and Fe3+/ΣFe ratios from 0.136 to 0.177. These compositions are similar to MORB and suggest that decompression melting of dry and reduced mantle dominates the earliest stages of subduction initiation. Low‐ and high‐silica boninite glasses have 1.51–3.19 wt% H2O, CO2below detection, S contents below those required for sulfide saturation (5–235 ppm), Ba/La from 11 to 29, and Fe3+/∑Fe from 0.181 to 0.225. The compositions are broadly similar to modern arc lavas in the IBM arc. These data demonstrate that the establishment of fluid‐fluxed melting of the mantle, which occurs in just 0.6–1.2 my after subduction initiation, is synchronous with the production of oxidized, mantle‐derived magmas. The coherence of high Fe3+/∑Fe and Ba/La ratios with high H2O contents in Expedition 352 glasses and the modern IBM arc rocks strongly links the production of oxidized arc magmas to signatures of slab dehydration.
-
more » « less
Abstract Two-thirds of the Earth is covered by mid-ocean ridge basalts, which form along a network of divergent plate margins. Basalts along these margins display a chemical diversity, which is consequent to a complex interplay of partial mantle melting in the upper mantle and magmatic differentiation processes in lower crustal levels. Igneous differentiation (crystal fractionation, partial melting) and source heterogeneity, in general, are key drivers creating variable chemistry in mid-ocean ridge basalts. This variability is reflected in iron isotope systematics (expressed as δ57Fe), showing a total range of 0.2 ‰ from δ57Fe = + 0.05 to + 0.25 ‰. Respective contributions of source heterogeneity and magma differentiation leading to this diversity, however, remain elusive. This study investigates the iron isotope systematics in basalts from the ultraslow spreading Gakkel Ridge in the Arctic Ocean and compares them to existing data from the fast spreading East Pacific Rise ridge. Results indicate that Gakkel lavas are driven to heavier iron isotope compositions through partial melting processes, whereas effects of igneous differentiation are minor. This is in stark contrast to fast spreading ridges showing reversed effects of near negligible partial melting effects followed by large isotope fractionation along the liquid line of descent. Gakkel lavas further reveal mantle heterogeneity that is superimposed on the igneous differentiation effects, showing that upper mantle Fe isotope heterogeneity can be transmitted into erupting basalts in the absence of homogenisation processes in sub-oceanic magma chambers.
-
more » « less
Abstract Delineation of geochemically distinct domains in Earth’s mantle is essential for understanding large-scale mantle convective flow and dynamics. Previous studies identify possible long-lived (>60 million-year) mantle isotopic domains (i.e. Antarctic-Zealandia, Pacific and Indian) near the Philippine Sea and western Pacific. Here we compile published basalt geochemistry of the Philippine Sea and surroundings and add new Mo isotopic and water content data for Gagua Ridge lavas, northwestern Philippine Sea, to distinguish slab-derived components during subduction. The water content, trace element, and Mo-Sr-Nd isotope compositions of Gagua Ridge arc lavas suggest that slab fluids and sediment melts are responsible for element recycling to the arc. The Philippine Sea basalts show both Indian and Zealandia-Antarctic Pb isotopic signatures; restoration of the basalt locations within a plate reconstruction shows the far-travelled Philippine Sea traversed these mantle domains. We establish the Indian mantle domain eastern boundary at ~120°E under SE Asia and the Indian Ocean. The Antarctic-Zealandia mantle domain lies south of ~10°N within the SW Pacific and has mostly remained in oceanic realms since ~400 Ma with only limited continental material input.
-
PhD Dissertation Abstract: The imposing andesite stratovolcano is the characteristic expression of subduction zone magmatism, posing hazards to coastal populations and bearing insight into deep Earth processes. On a map of a typical volcanic arc, one can easily distinguish the approximately linear alignment and regular spacing of these major edifices that stand out from a diffuse distribution of mafic volcanoes (e.g. the Quaternary Cascades; Hildreth, 2007). The andesitic composite volcanoes have a reputation for being complex, open systems: crystal zoning “stratigraphies,” diverse crystal cargoes including antecrysts or xenocrysts, quenched magmatic inclusions, and variations in isotopic signatures are among the many lines of evidence that these systems involve a variety of igneous processes and melt sources. To investigate the development and evolution of such transcrustal magma factories, I have conducted a detailed temporal, spatial, and geochemical characterization of a long-lived arc volcanic center in the southern Washington Cascades, the Goat Rocks volcanic complex. Results from ⁴⁰Ar/³⁹Ar and U/Pb geochronology constrain the lifespan of the Goat Rocks volcanic complex from ~3.1 Ma to ~100 ka. During this time, four major composite volcanoes were built (as well as several smaller volcanoes). From oldest to youngest, these are Tieton Peak, Bear Creek Mountain, Lake Creek volcano, and Old Snowy Mountain. Four volcanic stages are defined based on the lifespans of these centers and distinct compositional changes that occur from one to the next: Tieton Peak stage (3.1-2.6 Ma), Bear Creek Mountain stage (1.6-1.1 Ma), Lake Creek stage (1.1 Ma to 456 ka), and Old Snowy Mountain stage (440 ka to 115 ka). Two lava flow remnants also have ages in the interim between Tieton Peak stage and Bear Creek Mountain stage (2.3 Ma and 2.1 Ma), and their sources are not yet identified. The ages of the Bear Creek Mountain and Lake Creek stages in fact overlap, and the gap between Lake Creek stage and Old Snowy Mountain stage is only on the order of 10⁴ years. Based on supporting compositional evidence, the Bear Creek Mountain, Lake Creek, and Old Snowy Mountain stage volcanoes are considered to be the migrating surface expressions of a continuous magmatic system that was active over at least ~1.5 million years. It remains uncertain whether the gaps between the Tieton Peak stage, scattered early Pleistocene andesites, and Bear Creek Mountain stage are due to incomplete exposure/sampling or real quiescent periods earlier in the development of the Goat Rocks volcanic complex. Throughout the construction of the andesitic complex, mafic volcanoes were active on its periphery. These include the Miriam Creek volcano (~3.6-3.1 Ma), Devils Washbasin volcano (3.0-2.7 Ma), Hogback Mountain (1.1 Ma – 891 ka), Lakeview Mountain (194 ka), and Walupt Lake volcano (65 ka). Two basalt and basaltic andesite units (Qob₁ and Qob₂, 1.4 and 1.3 Ma; Hammond, 2017) also erupted from the Goat Rocks area, likely an older incarnation of Hogback Mountain. The suite of mafic magmas erupted in this region are all calcalkaline basalt (or basaltic andesite; CAB), but two compositional groups emerge from the trace element and isotopic data. Group 1 is LILE and LREE-enriched, with higher ⁸⁷Sr/⁸⁶Sr isotopes, and includes compositions from Devils Washbasin, Lower Hogback Mountain, and Lakeview Mountain. Group 2 is less enriched in LILE and LREE and lower in ⁸⁷Sr/⁸⁶Sr, and includes the compositions of Miriam Creek, Qob1, Upper Hogback Mountain, Walupt Lake, and Coleman Weedpatch. The two groups are recurrent through time and with no geographic distinction; in fact, both types were tapped by the Hogback Mountain volcano. Together both of these groups, alongside CABs from Mount Adams and various basalts from Mount St. Helens, form a compositional array between the basalts of the High Cascades and the intraplate-type basalts (IPB) of Mount Adams and Simcoe volcanic field. These results lead to three conclusions. 1) Variably subduction-modified mantle is distributed across the region, perhaps either as stratified layers or a web-like network of fluid pathways amongst less metasomatized mantle. 2) Transitional compositions between the IPBs and typical “High Cascades” CAB/HAOT signature suggest a broader influence of the mantle domain that feeds IPBs—if asthenospheric mantle through a slab window, as suggested by Mullen et al. (2017), then perhaps it bleeds in smaller quantities over a broader area. This compositional trend solidifies the interpretation of the southern Washington Cascades as a unique and coherent “segment” of the arc (the Washington segment of Pitcher and Kent, 2019). 3) The recurrence of variable mafic magma types through time, and with no geographic boundaries, indicates that the compositional evolution of the Goat Rocks volcanic complex was not likely driven by a change in mafic input. Indeed, the Sr, Nd, Hf, and Pb isotope ratios of the intermediate to felsic suite are closely aligned with the local basalts and suggest a limited role of crustal assimilation. Importantly, several mineral thermometers (zircon, ilmenite-magnetite pairs, and amphibole) align in recording higher crystallization temperatures in Bear Creek Mountain to early Lake Creek time, a cooling trend through the Lake Creek stage, and a more diverse range of temperatures in the transition to Old Snowy Mountain stage. Thus, it is suggested that the compositional evolution at Goat Rocks represents a thermal cycle of waxing and waning magmatic flux: where the period of Bear Creek Mountain to early Lake Creek volcanism was the climactic phase of a vertically extensive magma homogenization factory, then the system waned and cooled, ultimately losing its ability to filter, homogenize, and enrich magmas.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-021-25027-2
