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Vargas, JA, Hilton DR, Ramirez C, Molina J.  2018.  Metals in bivalve mollusks from the Jaco Scar seep, Pacific, Costa Rica. Revista De Biologia Tropical. 66:S269-S279. AbstractWebsite

Deep sea-research has made significant discoveries thanks to the availability of high resolution bathymetric mapping and vehicles able to reach hydrothermal vents and cold seeps. The Pacific continental margin of Costa Rica includes cold seeps that are inhabited by vesicomyid clams, which are expected to accumulate metals. Data on metals from cold seep clams are scarce. Thus, the objective of this study is to present the concentrations of Al, Cd, Cu, Fe, Pb, Mn, Ni, Sb and Zn in samples from seven clams, a mussel, sediment, and a rock, together with clam morphometric data. The bivalves (Archivesica sp.?) were collected in 2005 at a depth of 1888 m on the Jaco Scar (09 degrees 06' N - 84 degrees 50' W) during DSRV Alvin dive 4129. Metals were analyzed by Flame Atomic Absorption Spectrometry (FAAS) and Graphite Furnace (GFAAS). Concentrations are in mu g/g dry weight. The order of decreasing maximm concentrations and range in tissues of seven clams, were: Zn (43.4 - 266.3) > Fe (27.2 - 100.0) > Al (5.0 - 69.9) > Cd (0.1 - 12.2) > Sn (2.8 - 9.5) > Cu (4.0 - 7.3) > Mn (1.1 - 2.2) > Pb (0.2 - 0.8) > Ni (0.19 - 0.58 ). The gills had the maximum concentrations of Fe and Al. Maximum concentrations in the only mussel specimen collected, were: Zn (80.4 - gills), Fe (70.6 - gills). Cu (31.0 - gills). Al (26.6 - gills), Sn (4.8 - mantle), Mn (1.7 - mantle). Ni (0.97 - muscle), Pb (0.7 - muscle), Cd (0.57 - gills). The sediment sample had: Al (40 800), Fe (26 500), Mn (72.0), Zn (64.7), Cu (29.4), Ni (19.3), Sn (15.5). Pb (2.98), Cd (0.16). A rock fragment had: Fe (15 650), Al (9 240), Mn (170), Sn (99.5), Zn (36.5), Ni (20.4), Cu (13.4), Pb (1.6), Cd (traces). Clam gills concentrated metals such as Fe and Al. Fe was below the range reported for hydrothermal vent clams. while concentrations of other metals were near the lower range. Fe, Cd, Mn, and Pb in mussel tissues were lower than those in mussels from hydrothermal vent sites, while Cu and Zn were within the range. Metals in the sediment and rock samples appeared very rich in certain metals like Al and Fe and very poor in others, such as Cd. There is a paucity of information on metals and pollutants in clams and other macrofaunal species from Costa Rican cold seeps. Data presented herein must be complemented with future studies conducted jointly on the geochemistry, biology. and management of these deep-sea systems.

Haroardottir, S, Halldorsson SA, Hiltons DR.  2018.  Spatial distribution of helium isotopes in Icelandic geothermal fluids and volcanic materials with implications for location, upwelling and evolution of the Icelandic mantle plume. Chemical Geology. 480:12-27.   10.1016/j.chemgeo.2017.05.012   AbstractWebsite

The distribution of helium isotope ratios (He-3/He-4) in Icelandic geothermal fluids, volcanic glasses and phyric lavas is investigated. Along with presenting a new helium isotope dataset using phyric lavas largely from off-rift regions, we compiled published data and constructed a database of all available helium isotope data from Iceland. The new dataset reveals an exceptionally high He-3/He-4 ratio from a phyric lava in NW-Iceland (47.5 R-A, where R-A is the He-3/He-4 ratio of air), which is among the highest values measured in any mantle-derived magma to date. Modifications of primary (i.e., mantle-derived) helium isotope ratios, due to additions of air-derived helium and He from radiogenic ingrowth, were evaluated and the database was filtered accordingly. The geographical information system ArcGIS (ESRI) was used to perform spatial analysis on the filtered database and the interpolation method, Natural Neighbor, was used to calculate representative helium isotope ratios for all parts of Iceland, including off-rift regions. The results show that helium isotope ratios for the whole of Iceland vary from 5.1 to 47.5 R-A. However, this study allows for a fine-scale distinction to be made between individual rift segments and off-rift regions. The results clearly reveal that each rift zone has its own distinctive mean isotope signature: 12-17 R-A in the Western Rift Zone, 8-11 R-A in the Northern Rift Zone and 18-21 R-A in the Eastern Rift Zone. Our isoscape map places new constraints on a previously inferred high-helium plateau region in central Iceland (Breddam a al., 2000). The plateau continues southward along the propagating Eastern Rift Zone and through to the South Iceland Seismic Zone and the Mid-Iceland belt. Its location coincides with many geological features, e.g., eruption rates, location of abandoned rift segments, seismic velocity and gravity anomalies. Such high helium isotope ratios have been associated with undegassed and primordial mantle sources that have been isolated in the lower mantle over Earth's history. Thus, high-helium domains throughout Iceland are interpreted to mark the loci of present and past plume conduits which help explain the considerable spatial variation in the sampling of a primordial mantle He component beneath the Iceland hotspot.

Gulec, N, Hilton DR.  2006.  Helium and heat distribution in western Anatolia, Turkey; relationship to active extension and volcanism. Special Paper Geological Society of America. 409:305-319.   10.1130/2006.2409(16)   Abstract

Western Anatolia, one of the world's best-known extensional terrains, is characterized by the presence of several moderate- to high-enthalpy geothermal fields. Geo-thermal fluids have helium isotope compositions reflecting mixing between mantle and crustal helium components, the former ranging between 0.58% and 45% of the total helium in a given sample. Regarding the distribution of heat and mantle He and their correlation with tectonic structure and volcanism in western Anatolia, the prominent features are as follows: (1) the association between highest heat and highest (super 3) He lies along the eastern segment of the Buyuk Menderes graben, (2) the high heat and high (super 3) He occur in the vicinity of the Quaternary Kula volcanism, (3) high-enthalpy fields exist in close vicinity to the young alkaline volcanics, (4) relatively high mantle He contributions occur in areas of not only the young alkaline, but also the old calc-alkaline volcanics, and (5) there is a lack of volcanic exposures along the Buyuk Menderes graben (except at its western and southeastern terminations), where the highest values are recorded for both heat and helium. The first three features collectively suggest that the transfer mechanism for both heat and helium is probably mantle melting accompanying the current extension in western Anatolia, yet the latter two further indicate that this may be accomplished via subsurface plutonic activities. The large range observed in the helium isotope compositions may be linked with differential (local) extension rates and associated melt generation in the respective areas. This suggestion can be substantiated by He isotope data from more of the region.

Hilton, DR, Hoogewerff JA, Vanbergen MJ, Hammerschmidt K.  1992.  Mapping Magma Sources in the East Sunda-Banda Arcs, Indonesia - Constraints from Helium Isotopes. Geochimica Et Cosmochimica Acta. 56:851-859.   10.1016/0016-7037(92)90105-r   AbstractWebsite

We report new helium isotope analyses of olivine and clinopyroxene separates from recent lavas for eleven volcanoes from Flores in the east Sunda arc through the inactive segment between the arcs to Banda Island at the extreme of the contiguous Banda arc. In the east Sunda arc, He-3/He-4 (R) vary between 4.5R(A) (R(A) = air He-3/He-4) for the leucitic Batu Tara volcano to a remarkable low of pure radiogenic helium (0.0075 R(A)) for Werung at the southern tip of Lomblen Island. Lavas from the inactive zone, which represents the locus of collision of the Australian continent with the arc, have a narrower range in R/R(A)from 3.9 for Kisu in the straits of Pantar to 1.0 for Romang Island. Our one locality (Banda Island) in the Banda arc gives the highest R/R(A) ratio (3.1) observed along this arc to date. The results are consistent with the involvement of crustal material in magma genesis throughout the east Sunda/Banda arcs, as far west as Iya in central Flores. We combine these helium isotope results with published and on-going strontium isotope studies, and show that the source of the helium in the crustal component is unlikely to be terrigenous sediments derived from the Australian continent; rather, degassing of Australian continental crust appears to be the dominant process controlling the helium budget. The He-Sr isotope systematics also provide a framework to account for the areal pattern of He-3/He-4 in this part of the arcs: the radiogenic crustal component is diluted with mantle helium both in a down-dip direction and with increasing lateral distance from the collision zone. These factors result in an excellent first-order relationship between the He-3/He-4 ratio, degree of He/Sr enrichment (relative to the postulated mantle endmember), and alkalinity of the erupted lavas. Such a relationship has a direct bearing on models of the tectonic evolution of the collision zone, and on the observation that helium isotopes are decoupled from strontium and other geochemical signatures along the Banda arc.