Geology topics

Jun-Ichi Kimura

Publications and source records attributed to Jun-Ichi Kimura.

4 recordsLinked to original sources

USGS2010

Source materials for inception stage Hawaiian magmas: Pb‐He isotope variations for early Kilauea

New noble gas and radiogenic isotopic compositions are presented for tholeiitic, transitional, and alkalic rocks from the submarine Hilina region on the south flank of Kilauea, Hawaii. The 3 He/ 4 He ratios for undegassed glass and olivine separates (11–26 Ra) contrast with those of postshield and rejuvenated alkalic lavas, consistent with the alkalic and transitional basalts at Hilina corresponding to early Kilauea magmas. Most early Kilauea samples contain highly radiogenic Pb isotopes compared with other Hawaiian rocks and therefore derive from a Hawaiian plume end‐member source (here referred to as the Hilina component) distinctive in that respect. Besides radiogenic Pb isotopes, the Hilina component has relatively low 3 He/ 4 He (<12 Ra) among the Hawaiian magmas. Hawaiian inception stage magmas, including Hilina, Loihi, and deep Hana Ridge (east Maui), define a linear array in 206 Pb/ 204 Pb‐ 3 He/ 4 He isotope space, indicating that mixing between the Hilina and Loihi components (or their melts) dominates magmatism at the leading edge of the Hawaiian plume. The Hilina component's isotopic characteristics can be derived from young subduction‐recycled crust or metasomatised mantle. The isotopic differences between the geographically discriminated Kea and Loa trend volcanic chains, observed in shield stage lavas, are also seen in the inception stage magmas, suggesting that proportions of melts derived from the Hilina and Loihi components were different between the Kea and Loa trend volcanoes.

Hawaii↗

USGS2009

Basanite-nephelinite suite from early Kilauea: Carbonated melts of phlogopite-garnet peridotite at Hawaii's leading magmatic edge

A basanite-nephelinite glass suite from early submarine Kilauea defines a continuous compositional array marked by increasing concentrations of incompatible components with decreasing SiO 2 , MgO, and Al 2 O 3 . Like peripheral and post-shield strongly alkalic Hawaiian localities (Clague et al. in J Volcanol Geotherm Res 151:279-307, 2006; Dixon et al. in J Pet 38:911-939, 1997), the early Kilauea basanite-nephelinite glasses are interpreted as olivine fractionation products from primary magnesian alkalic liquids. For early Kilauea, these were saturated with a garnet-phlogopite-sulfide peridotite assemblage, with elevated dissolved CO 2 contents responsible for the liquids' distinctly low-SiO 2 concentrations. Reconstructed primitive liquids for early Kilauea and other Hawaiian strongly alkalic localities are similar to experimental 3 GPa low-degree melts of moderately carbonated garnet lherzolite, and estimated parent magma temperatures of 1,350-1,400??C (olivine-liquid geothermometry) match the ambient upper mantle geotherm shortly beneath the base of the lithosphere. The ???3 GPa source regions were too hot for stable crystalline carbonate and may have consisted of ambient upper mantle peridotite containing interstitial carbonate-silicate or carbonatitic liquid, possibly (Dixon et al. in Geochem Geophys Geosyst 9(9):Q09005, 2008), although not necessarily, from the Hawaiian mantle plume. Carbonate-enriched domains were particularly susceptible to further melting upon modest decompression during upward lithospheric flexure beneath the advancing Hawaiian Arch, or by conductive heating or upward drag by the Hawaiian mantle plume. The early Kilauea basanite-nephelinite suite has a HIMU-influenced isotopic character unlike other Hawaiian magmas (Shimizu et al. in EOS Tran Amer Geophys Union 82(47): abstr V12B-0962, 2001; Shimizu et al. in Geochim Cosmochim Acta 66(15A):710, 2002) but consistent with oceanic carbonatite involvement (Hoernle et al. in Contrib Mineral Petrol 142:520-542, 2002). It may represent the melting products of a fertile domain in the ambient upper mantle impinged upon and perturbed by the sustained plume source that feeds later shield-stage magmatism. ?? US Government 2009.

Contributions to Mineralogy and Petrology↗

USGS2006

Submarine sliver in North Kona: A window into the early magmatic and growth history of Hualalai Volcano, Hawaii

Two manned submersible dives examined the Hualalai Northwest rift zone and an elongate ridge cresting at 3900 mbsl during a 2002 JAMSTEC cruise. The rift zone flank at dive site S690 (water depth 3412–2104 m) is draped by elongated and truncated pillow lavas. These olivine-rich tholeiitic lavas are compositionally indistinguishable from those examined further south along the bench, except that they span a wider range in dissolved sulfur content (200–1400 ppm). The elongate ridge investigated in dive S692, located at the base of the bench, is a package of distinct lithologic units containing volcaniclastic materials, glassy pillow breccias, and lava blocks; these units contain a range of compositions including tholeiitic basalt, transitional basalt, and hawaiite. The textures, compositions, and stratigraphic relationships of materials within the elongate ridge require that a variety of transport mechanisms juxtaposed materials from multiple eruptions into individual beds, compacted them into a coherent package of units, and brought the package to its present depth 10 km from the edge of the North Kona slump bench. Sulfur-rich hawaiite glasses at the base of the elongate ridge may represent the first extant representatives of juvenile alkalic volcanism at Hualalai. They are geochemically distinct from shield tholeiite and post-shield alkalic magmas, but may be related to transitional basalt by high-pressure crystal fractionation of clinopyroxene. Tholeiitic glasses that compose the majority of the exposed outcrop are similar to Mauna Kea tholeiites and other Hualalai tholeiites, but they differ from younger basalts in having greater incompatible element enrichments and higher CaO for a given MgO. These differences could arise from small extents of partial melting during the transition from alkalic to shield stage magmatism. Low sulfur contents of most of the volcaniclastic tholeiites point to early emergence of Hualalai above sea level relative to the development of the midslope slump bench.

Hawai'i↗

USGS2004

Ultra-high chlorine in submarine Kı̄lauea glasses: Evidence for direct assimilation of brine by magma

Basaltic glass grains from the submarine south flank of Kı̄lauea, Hawai′i, have Cl concentrations of 0.01–1.68 wt%, the latter being the highest Cl content yet recorded for a Hawaiian glass. The high-Cl glass grains are products of brine assimilation by tholeiite magma. The glasses are grains in a sandstone clast from bedded breccias draping the southwestern margin of Kı̄lauea’s submarine midslope bench. The clast contains two distinct suites of glass grains: abundant degassed tholeiites, perhaps derived from subaerial lavas of Mauna Loa that shattered upon ocean entry, and a smaller population of Kea-type tholeiite ( n =17 analyzed) that erupted subaqueously, based on elevated S (780–1050 ppm), H 2 O (0.42–1.27 wt%), and CO 2 (<30–120 ppm), probably early in Kı̄lauea’s shield-building stage. Ten grains in this group have Cl>1000 ppm, six >5000 ppm, and two grains have >10 000 ppm dissolved Cl. Abundances of H 2 O, Na 2 O, K 2 O, and several trace elements increase regularly with Cl concentration, and we estimate that Cl enrichment was due to up to 13 wt% addition of a brine consisting of 78% H 2 O (wt), 13% Cl, 4.4% Na, 2.6% K, 2.6% Ca, 620 ppm Ba, 360 ppm Sr, 65 ppm Rb, and 7 ppm Pb. The large amounts of brine addition argue against bulk assimilation of low-porosity brine-bearing rock. The brine’s composition is appropriate for a seawater-derived hydrothermal fluid that reacted with basaltic wall rocks at T >100°C, losing Mg and S and gaining K, Ca, Rb, Ba, Sr, and Pb, followed by phase separation near 500°C and ∼50 MPa (5 km below sea level at hydrostatic pressure). Brine was assimilated at or near the depth it formed, as estimated on petrologic grounds, but under lithostatic conditions. The highest extents of assimilation either forced volatile saturation of the magma or enriched already coexisting magmatic vapor in H 2 O. Possible mechanisms for assimilation are: (1) forcible injection of brine into magma during bursting of overpressured pockets heated by new dikes, or (2) intrusion of magma into lenses or sills occupied by trapped brine.

Hawaii↗