Diverse sources of volatile release across volcanic arcs: Insights from Kozelsky and Khangar volcanoes, Kamchatka
Ivan Savov & Dan Morgan (Univ. Leeds),
Tanja Churikova (Russian Acad. of Sciences-Far East [Kamchatka] Branch)
Alex Iveson (Durham Univ.)
The Kamchatka peninsula is one of the most volcanically active regions on Earth and is among the best places in the world to study the fate of subducted old (cold) oceanic crust. Uniquely the volcanoes of this arc erupt in several, rather than one, broad volcanic lineaments, possibly sampling magmatic fluid and melt sources in the forearc, beneath the main volcanic front and also from the behind-the-arc region. Recent geophysical and geochemical results (Churikova et al., 2001, 2007; Portnyagin et al., 2007; Portnyagin & Manea,, 2008 and ref. therein) show that the Kamchatka volcanoes indeed sample fluids derived from slab depths from as little as 50km to as deep as 350 km. While the majority of arc volcanoes (here and elsewhere in other arcs) result from flux melting of depleted subarc mantle wedge source, the geochemistry of the arc volcanic rocks (incl. 10Be, U- series, B & Li isotopes, B/Be, B/Nb and Sr/Y ratios, among others) also shows, sometimes significant elemental and isotopic inputs from subducted slabs. These may include subducted sediments, altered basaltic crust and/or fluids/melts resulting from the dehydration of serpentinized sections of the slabs or forearc-serpentinized (subarc) mantle wedge (Yogodzinski et al., 2001; Churikova et al., 2001, 2007; Portnyagin et al., 2007). Although the depleted mantle sources dominate the major and minor element budgets of the erupted products, the components released from the slab are geochemically traceable (Kepezhinskas et al., 1997; Ishikawa et al., 2001; Yogodzinski et al., 2001; Churikova et al., 2001, 2007) and have been shown to deliver the most important H2O, CO2, halogen and fluid mobile element (B, Cs, Li, As, Sb) contributions to arc magmas. However, the individual slab lithologies involved and their relative influence with depth, especially that originating from dehydration reactions in the deeply subducted serpentinites, has not been quantified yet.
This project aims to address this issue by examining the geochemistry and petrology of volcanic products erupted along a SE-NW oriented depth transect across the Eastern Volcanic Arc Front and deep into the rear arc (Sredinny Ridge) region. In previous fieldwork campaigns we have extensively sampled Avachinsky and Bakening volcanoes that are ideally situated in the middle of cross-arc transect and represent depths to the top of the slab of 120 to 200 km., respectively. Here we will aim to conduct fieldwork in Kamchatka (2020 and/or 2021) and sample and study the volatile and fluid mobile element systematics in one additional shallow-sourced (<100 km, Kozelsky) and one very deeply sourced (>300 km Khangar) volcanoes from the same (arc front orthogonal) transect.
Top: Part of the shallow cross-arc volcano transect including (from left to right) Koryaksky, Avachinsky and the unstudied Kozelsky Pleistocene-Holocene volcanoes. Note that these are located <12 km from the nearby major populated city of Petropavlovsk; Right: Location of main Holocene volcanoes (cirles) of Kamchatka and the location of the main volcanic lineaments in respect to the Kurile-Kamchatka Trench and the proposed across-arc transect (highlighted). Red arrows indicate the relative position of the unstudied Kozelsky and Khangar volcanoes.
Kozelsky volcano is Pleistocene in age low-K andesitic volcano, situated in the shallowest segments of the Kamchatka subduction zone. Although it is one of the large volcanoes proximal to the town of Petropavlovsk (population ~170 000)- it is not extensively studied and sampled. We hope to be able to sample mafic rocks from several cinder cones on the flanks of Kozelsky volcano. We hypothesize that this volcano should sample very high volatile fluxes and the majority of the fluid mobile elements should be derived from the shallowly dehydrating trench sediments and the associated subducted forearc-serpentinized subarc mantle.
Khangar caldera hosts the southernmost volcanic centers of Sredinny Ridge and those are representing the deepest sourced rear- arc magmatism in Kamchatka. Various domes and ignimbrites here sample Holocene eruptions as young as 500 yrs. ago. About 7000 yrs. ago it exploded in Plinian (VEI= 6) eruption that produced ash that reached as far as Greenland and with total estimated volume of ~ 16 km3 (Braitseva et al., 1995; GVP-Smithsonian Inst.). Most of the deposits are high-K dacites that contain hornblende and biotite, but there are some mafic (picritic) materials south of the caldera and those will be the primary targets. We hypothesize that this volcano should sample very low quantity of slab volatiles and that the bulk of the fluid mobile elements would be derived from the serpentinized lithospheric mantle section of the subducted Pacific slabs and altered (gabbroic) part of the subducted (Pacific) crust.
The olivine- and pyroxene- bearing mafic samples (preferably scoria) we collect will be used to extract melt inclusions (MI) from the mafic minerals (ol, px, hbl). The MI will be complementary to already available (in Durham and Leeds) Kamchatka arc MI collection. The new MI will be adding, for the first time, an exceptional high resolution look at the petrochemical variations across active volcanic arc. Moreover, we will uniquely have a chance to examine compositional changes of slab derived fluxes with increasing depth-to-slab. The proposed transect will be complementary to a cross arc transect to the north (Churikova et al., 2007), although the slab depths/geometry and the overlaying terrain boundaries there are less clear when compared with the newly proposed transect, where the Benioff zone is clearly delineated by deep regional seismicity and tomography.
The project will involve training and use of various in-situ measurement techniques such as SEM, EPMA, LA-ICP-MS and SIMS (for the MI). We will provide training (mostly in-house) in textural/petrological observations, sample selection and preparation and geochemical modelling based on bulk rock and MI datasets.
Khangar Caldera in the southernmost rear arc (Sredinny Ridge) of Kamchatka. Magmas erupted here include 16km3 ignimbrites and post ignimbrite arc picrites (with abundant olivine). These materials may sample volatile and fluid components originating from deeply (>300 km) subducted slabs.
The Candidate: This project will be integral part of a larger NERC-funded consortia (Deep Mantle Volatiles), where global volatile cycles (including from Kamchatka) will be reviewed via many other (and complementary) techniques. Key samples for this study are already in Leeds or Durham (from Avachinsky and Bakening volcanoes), but fieldwork to complete/extend the sample suite and to better understand the local geological setting is planned. The wide range of techniques require a multidisciplinary training and approach, which will be covered by the wide range of facilities available in one of the leading schools for petrology and geochemistry in the UK and Europe- Leeds, Durham. The student will be based in Leeds, where s/he will be able to interact with large and very active research groups in the broad fields of Volcanology and High-T geochemistry. More info on these groups members can be found here:
Preference will be given to candidates who have prior experience and solid training in the fields of petrology and geochemistry and/or MI sample preparation and in-situ analysis. Ability to carry collaborative fieldwork in isolated mountainous terrain and in remote (Arctic) wilderness are not required but will be a plus.
Fit to NERC Science, Training and Support:
This student project is highly relevant and excellent fit to the ongoing NERC-funded (5 yrs.) Deep (Mantle) Volatiles Consortia (http://www.deepvolatiles.org), where Savov is a Co-PI. Savov and Churikova are actively involved in the consortia project design and in the fieldwork and training of three postdocs (including one (A.I.) to co-supervise (this) project) and two PhD students that are examining aspects of the elemental and isotope cycles across subduction zones, including in Kamchatka. The elemental cycles on Earth and specifically the fate of volatiles and fluids have been outlined as a primary target for the understanding of Planet Habitability and so the proposed project is a direct fit to the NERC science. The vast interest in the convergent margin processes (incl. popular and applied science involving the “Ring of Fire”) and the fact that volatile releases at these settings govern volcano explosivity and earthquake distributions, the proposed project is directly linked to adding scientific knowledge aiding realistic hazard assessments and preventing loss of life. Considering how little is known about the proposed volcanoes and the uniqueness of their position relative to an actively subducting Pacific plate and the most populated area in Kamchatka (<12 km from Petropavlovsk), the results from this project will have no problem to generate highly referenced and influential (4*) future publications.
Selected relevant literature:
Braitseva, O., Melekestsev, I., Ponomareva, V., Sulerzhitsky, L., 1995, Ages of calderas, large explosive craters and active volcanoes in the Kuril-Kamchatka region, Russia: Bulletin of Volcanology 57, 383-402.
Churikova, T., Dorendorf, F., Wörner, G. (2001). Sources and Fluids in the Mantle Wedge below Kamchatka, Evidence from Across- Arc Geochemical Variation, J. Petrology 42, 1567-1593.
Churikova, T., Worner, G., Mironov, N., Kronz, A. (2007). Volatile (S, Cl and F) and fluid mobile trace element compositions in melt inclusions: implications for variable fluid sources across the Kamchatka arc, Contrib Mineral Petrol 154, 217-239.
Ishikawa, T., Tera, F., Nakazawa, T., 2001, Boron isotope and trace element systematics of the three volcanic zones in the Kamchatka arc: Geochim. Cosmochim. Acta 65, 24, 4523-4537.
Kepezhinskas, P., McDermott, F., Defant, M.J., Hochstaedter, A., Drummond, M.S., Hawkesworth, C.J., Koloskov, A., Maury, R., Bellon, H., 1997, Trace element and Sr-Nd-Pb isotopic constraints on a three-component model of Kamchatka arc petrogenesis: Geochim. Cosmochim. Acta 61, 3, 577-600.
Portnyagin, M., Hoernle, K., Plechov, P., Mironov, N. and Khubunaya, S. 2007. Constraints on mantle melting and composition and nature of slab components in volcanic arcs from volatiles (H2O, S, Cl, F) and trace elements in melt inclusions from the Kamchatka Arc. Earth Planet. Sci. Lett. 255, 53-69.
Portnyagin, M. and Manea, V., 2008. Mantle temperature control on composition of arc magmas along the Central Kamchatka Depression. Geology 36(7), 519-522.
Yogodzinski GM, Lees JM, Churikova TG, Dorendorf F, Wörner G, Volynets O. (2001). Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges. Nature 409, 500-504.