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Rosalind Tuthill Helz

Publications and source records attributed to Rosalind Tuthill Helz.

33 records · Page 2Linked to original sources
USGS1991

Reequilibration of chromite within Kilauea Iki lava lake, Hawaii

Chromite mainly occurs as tiny inclusions within or at the edges of olivine phenocrysts in the 1959 Kilauea Iki lava lake. Liquilus chromite compositions are only preserved in scoria that was rapidly quenched from eruption temperatures. Analyses of drill core taken from the lava lake in 1960, 1961, 1975, 1979, and 1981 show that chromite becomes richer in Fe+2, Fe+3, Ti and poorer in Mg, Al, Cr than the liquidus chromite. The amount of compositional change depends on the time elapsed since eruption, the cooling history of the sample, the extent of differentiation of the interstitial melt, and the position of the chromite inclusion within the olivine phenocryst. Compositional changes of the chromite inclusions are thought to be a result of reequilibration with the residual melt by cationic diffusion (Mg, Al, Cr outwards and Fe+2, Fe+3, Ti inwards) through olivine. The changing chemical potential gradients produced as the residual melt cools, crystallizes and differentiates drives the reequilibration process. Major and minor element zoning profiles in olivine phenocrysts suggest that volume diffusion through olivine may have been the major mechanism of cationic transport through olivine. The dramatic compositional changes observed in chromite over the 22 years between eruption and 1981 has major implications for othe molten bodies. ?? 1991 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1990

U-Pb and Sm-Nd ages for the Stillwater Complex and its associated sills and dikes, Beartooth Mountains, Montana: Identification of a parent magma?

Seven analyses from two samples of the Lower Banded series of the Stillwater Complex, Montana, yielded a U-Pb zircon-baddeleyite age of 2705 ±4 Ma. A more precise age of 2704 ±1 Ma is obtained if we regress only five of seven analyses. In either case, the age is in very good agreement with the previously reported Sm-Nd mineral isochron age of 2701 ±8 Ma for a gabbro from the Lower Banded series. Noncumulate mafic sills and dikes that immediately underlie the Stillwater Complex are separated into five compositional groups. U-Pb zircon ages for a group 1 gabbronorite (2711 ±1 Ma) and a group 3 mafic norite (2703 ±10 Ma) are comparable to previously reported U-Pb zircon ages for a group 1 diabase (2713 ±3 Ma) and a group 4 high-Ti norite (2712 ±3 Ma). Although group 2 high-Mg gabbronorite and group 6 olivine gabbro have not yet yielded significant amounts of zircon, baddeleyite, or sphene, mineral separates from group 2 ielded a four-point Pb-Pb internal isochron age of 2704 ±25 Ma, and separates from group 6 yielded a Sm-Nd internal isochron age of 2706 ±64 Ma, indicating that these groups are at least contemporaneous with intrusion of the Stillwater Complex. These results indicate that groups 1 and 4 of the associated sills and dikes are perhaps slightly older than the complex and that groups 2, 3, and 6 may be coeval with it, supporting the idea that these three groups are the best candidates for a Stillwater parent magma, a conclusion previously presented on the basis of detailed mineralogic and geochemical evidence.

Geology↗
USGS1989

Diapiric transfer of melt in Kilauea Iki lava lake, Hawaii: A quick, efficient process of igneous differentiation

Kilauea Iki lava lake, formed in 1959, is a large pond of picritic basalt (average MgO content = 15.34% by weight), which has cooled and crystallized as a small, self-roofed magma chamber. Repeated drilling of the upper crust of the lake, down to its molten core, and more recent (1981) drilling, through the thermal maximum and part way through the lower crust, have made it possible to monitor the differentiation processes in the lake in detail. Differentiation processes recognized as active in the lake include rather inefficient settling of the larger (2-10 mm) olivine phenocrysts, formation of segregation veins, and formation of diapir-like vertical olivine-rich bodies, all processes which occur in one or more of the other Kilauean lava lakes as well. In addition, most of the central part of Kilauea Iki has been affected by diapiric melt transfer. In this process, relatively low-density liquid, present at 1145-1160 °C, rose from within the loose crystal mush at the base of the lens of melt and intruded the equivalent thermal horizon at the top of the lens of melt, passing through the hotter but denser melt in the core of the lake without mixing. The source volume from which the low-density liquid was extracted is depleted in TiO 2 and other incompatible elements and enriched in FeO and CaO. The upper part of the lake shows the opposite effects. The crystalline assemblage present was olivine + augite + minor plagioclase. The crystallinity of both the source and receiving layers was low enough that no obvious textural imprint was left by the transfer process; the principal evidence for its occurrence is the chemical zonation of the lake seen in core from depths of 13 to 80 m. Diapiric melt transfer was active from 1960 to 1971 and has affected most of the central part of the lake from 13 m to at least 80 m. The process ran simultaneously with the other three main differentia tion processes but started and stopped independently of the others. Calculations suggest that between 21 and 42 wt % liquid has been extracted from the depleted zone at 56-78 m in the center of the lake, making this a very efficient process of chemical differentiation.

Hawaii↗
USGS1987

Geothermometry of Kilauea Iki lava lake, Hawaii

Data on the variation of temperature with time and in space are essential to a complete understanding of the crystallization history of basaltic magma in Kilauea Iki lava lake. Methods used to determine temperatures in the lake have included direct, downhole thermocouple measurements and Fe-Ti oxide geothermometry. In addition, the temperature variations of MgO and CaO contents of glasses, as determined in melting experiments on appropriate Kilauean samples, have been calibrated for use as purely empirical geothermometers and are directly applicable to interstitial glasses in olivine-bearing core from Kilauea Iki. The uncertainty in inferred quenching temperatures is ??8-10?? C. Comparison of the three methods shows that (1) oxide and glass geothermometry give results that are consistent with each other and consistent with the petrography and relative position of samples, (2) downhole thermo-couple measurements are low in all but the earliest, shallowest holes because the deeper holes never completely recover to predrilling temperatures, (3) glass geothermometry provides the greatest detail on temperature profiles in the partially molten zone, much of which is otherwise inaccessible, and (4) all three methods are necessary to construct a complete temperature profile for any given drill hole. Application of glass-based geothermometry to partially molten drill core recovered in 1975-1981 reveals in great detail the variation of temperature, in both time and space, within the partially molten zone of Kilauea Iki lava lake. The geothermometers developed here are also potentially applicable to glassy samples from other Kilauea lava lakes and to rapidly quenched lava samples from eruptions of Kilauea and Mauna Loa. ?? 1987 Springer-Verlag.

Bulletin of Volcanology↗
USGS1980

Crystallization history of Kilauea Iki lava lake as seen in drill core recovered in 1967-1979

Kilauea Iki lava lake formed during the 1959 summit eruption, one of the most picritic eruptions of Kilauea Volcano in the twentieth century. Since 1959 the 110 to 122 m thick lake has cooled slowly, developing steadily thickening upper and lower crusts, with a lens of more molten lava in between. Recent coring dates, with maximum depths reached in the center of the lake, are: 1967 (26.5 m). 1975 (44.2 m), 1976 (46.0 m) and 1979 (52.7 m). These depths define the base of the upper crust at the time of drilling. The bulk of the core consists of a gray, olivine-phyric basalt matrix, which locally contains coarser-grained diabasic segregation veins. The most important megascopic variation in the matrix rock is its variation in olivine content. The upper 15 m of crust is very olivine-rich. Abundance and average size of olivine decrease irregularly downward to 23 m; between 23 and 40 m the rock contains 5-10% of small olivine phenocrysts. Below 40 m. olivine content and average grainsize rise sharply. Olivine contents remain high (20-45%, by volume) throughout the lower crust, except for a narrow (< 6 m) olivine depleted zone near the basalt contact. Petrographically the olivine phenocrysts in Kilauea Iki can be divided into two types. Type 1 phenocrysts are large (1-12 mm long), with irregular blocky outlines, and often contain kink bands. Type 2 crystals are relatively small (0.5-2 mm in length), euhedral and undeformed. The variations in olivine content of the matrix rock are almost entirely variations in the amount of type 1 olivines. Sharp mineral layering of any sort is rare in Kilauea Iki. However, the depth range 41-52 m is marked by the frequent occurrence of steeply dipping (70??-90??) bands or bodies of slightly vuggy olivine-rich rock locally capped with a small cupola of segregation-vein material. In thin section there is clear evidence for relative movement of melt and crystals within these structures. The segregation veins occur only in the upper crust. The most widely distributed (occurring from 4.5-59.4 m) are thin veins (most < 5 cm thick), which cut the core at moderate angles and appear to have been derived from the immediately adjacent wall-rock by filter pressing. There is also a series of thicker (0.1-1.5 m) segregation veins, which recur every 2-3 m, between 20 and 52 m. These have subhorizontal contacts and appear, from similarities in thickness and spacing, to correlate between drill holes as much as 100 m apart. These large veins are not derived from the adjacent wallrock: their mechanism of formation is still problematical. The total thickness of segregation veins in Kilauea Iki is 3-6 m in the central part of the lake, corresponding to 6-11% of the upper crust. Whole-rock compositions for Kilauea Iki fall into two groups: the matrix rock ranges from 20-7.5% MgO, while the segregation veins all contain between 6.0 and 4.5% MgO. There are no whole-rock compositions of intermediate MgO content. Samples from < 12 m show eruption-controlled chemistry. Below that depth, matrix rock compositions have higher Al2O3, TiO2 and alkalies, and lower CaO and FeO, at a given MgO content than do the eruption pumices. The probable causes of this are assimilation of low-melting components from foundered crust, plus removal of olivine, plus removal of minor augite, for rocks with MgO contents of < 8.0%. Given the observed rate of growth of the upper crust, one can infer that significant removal of the type 1 olivine phenocrysts from the upper part of the lake began in 1963 and ceased sometime prior to 1972. The process. probably gravitative settling, appears to have been inhibited earlier by gas streaming from the lower part of the lens of melt. The olivine cumulate zone, which extends into the upper crust, contains relatively few (25-40%) olivine crystals, few of which actually touch each other. The diffuseness of the cumulate zone raises the possibility that the crystals were coated with a relatively visous boundary layer

Bulletin Volcanologique↗
USGS1980

A catalogue of drill core recovered from Kilauea Iki lava lake, from 1967 to 1979

The purpose of this report is to serve as a descriptive catalogue for drill core recovered from Kilauea Iki lava lake, from 1967 to 1979. Kilauea Iki lava lake was formed when lavas of the 1959 summit eruption were ponded in Kilauea Iki pit crater, a large pit crater at the extreme upper end of Kilauea's east rift zone (Fig. 1). This eruption is one of the best documented of Kilauean eruptions: Murata and Richter (1966) and Richter and Murata (1966) presented data on the chemistry and petrography of the lavas, respectively, and Richter et al. (1970) described the complex filling of the pit crater in considerable detail. Investigation of the lava lake began a few months after the crust stabilized, with the establishment of two perpendicular lines of levelling stations on the surface of the lake. In 1960-62, four holes were drilled through the upper crust in the center of the lake; the crust was 22-44 feet (6.7-13.4 m) thick at that time. Richter and Moore (1966) presented petrographic, modal, and chemical data on the core recovered from this early drilling. The upper crust of Kilauea Iki was drilled again in 1967 by staff members of the Hawaiian Volcano Observatory, and core was recovered from three holes. In 1975, U.S. Geological Survey workers drilled three more holes, each a few feet away from one of the 1 967 holes. A summary of all work done on Kilauea Iki and other Hawaiian lava lakes through 1975 has been given by Wright et al. (1976). The lake has been redrilled twice since 1975, by workers from Sandia Laboratories, as part of their Magma Energy Research program, in cooperation with the U.S. Geological Survey. In 1976, they drilled two holes near the center of the lake. In 1978-79, they drilled a total of six holes; one, commissioned by the U.S. Geological Survey, went completely through the lava lake near its north edge, into the pre-1959 lavas below.

Hawaii↗
USGS1980

The 1977 eruption of Kilauea volcano, Hawaii

Kilauea volcano began to erupt on September 13, 1977, after a 21.5-month period of quiescence. Harmonic tremor in the upper and central east rift zone and rapid deflation of the summit area occurred for 22 hours before the outbreak of surface activity. On the first night, spatter ramparts formed along a discontinuous, en-echelon, 5.5-km-long fissure system that trends N70??E between two prehistoric cones, Kalalua and Puu Kauka. Activity soon became concentrated at a central vent that erupted sporadically until September 23 and extruded flows that moved a maximum distance of 2.5 km to the east. On September 18, new spatter ramparts began forming west of Kalalua, extending to 7 km the length of the new vent system. A vent near the center of this latest fissure became the locus of sustained fountaining and continued to extrude spatter and short flows intermittently until September 20. The most voluminous phase of the eruption began late on September 25. A discontinuous spatter rampart formed along a 700-m segment near the center of the new, 7-km-long fissure system; within 24 hours activity became concentrated at the east end of this segment. One flow from the 35-m-high cone that formed at this site moved rapidly southeast and eventually reached an area 10 km from the vent and 700 m from the nearest house in the evacuated village of Kalapana. We estimate the total volume of material produced during this 18-day eruption to be 35 ?? 106 m3. Samples from active vents and flows are differentiated quartz-normative tholeiitic basalt, similar in composition to lavas erupted from Kilauea in 1955 and 1962. Plagioclase is the only significant phenocryst; augite, minor olivine, and rare orthopyroxene and opaque oxides accompany it as microphenocrysts. Sulfide globules occur in fresh glass and as inclusions in phenocrysts in early 1977 lavas; their absence in chemically-similar basalt from the later phases of the eruption suggests that more extensive intratelluric degassing occurred as the eruption proceeded. Bulk composition of lavas varied somewhat during the eruption, but the last basalt produced also is differentiated, suggesting that the magma withdrawn from the summit reservoir during the rapid deflation has not yet been erupted. ?? 1980.

Journal of Volcanology and Geothermal Research↗
USGS1973

Phase relations of basalts in their melting range at PH2O = 5 kb as a function of oxygen fugacity: Part I. Mafic phases

The phase relations of three basalts, the Picture Gorge tholeiite, the 1921 Kilauea olivine tholeiite, and the 1801 Hualalai alkali basalt, were studied at 5 kb water pressure, 680–1000°C, at the oxygen fugacities of the quartz-fayalite-magnetite (QFM) and hematite-magnetite (HM) buffers. In the range 680–850 °C, the crystalline assemblage on the QFM buffer is dominantly hornblende+ plagioclase, ± ilmenite, magnetite, sphene, fayalitic olivine, and phlogopitic mica. From 875 to 1000 °C the crystalline assemblage is hornblende+ olivine± augite+ ilmenite± magnetite. A melt phase is present from 700 to 1000 °C; a vapor phase was present in all charges. The hornblendes formed on the QFM buffer range in composition from common green hornblendes at low temperatures to kaersutitic hornblendes at 1000 °C. A1(IV) and Ti increase temperature. AI(VI) passes through a maximum near 825 °C, decreasing both above and below this temperature. AI(IV) is proportional to the sum A1(VI)+2Ti. There is a positive linear correlation of approximately 3 : 1 between AI(IV) and the number of cations in the A-site. The most likely explanation for this correlation at present is that the substitution of AI(VI) or Ti +4 for a divalent cation creates local charge imbalances in the amphibole structure which can be compensated only by further A-site substitution. There also appears to be a correlation between the a-cell dimension of hornblende and the A-site occupancy. Above a thresh hold value of approxmately 0.5 cations in A, a increases as A-site occupancy increases. Phase relations on the hematite-magnetite buffer are considerably simpler. The hornblendes show relatively little change in composition as temperature increases, and in the tholelitic compositions break down at or below 970 °C 35–60 °C above the first appearance of augite±olivine. The melting of hornblende is incongruent in all cases. The Fe-Ti oxides are pseudo-brookite and titanohematite; at 1000 °C these oxides make up 10 per cent by weight of the assemblage and contain most of the Tio 2 and FeO in the charge. The patterns of hornblende variation observed in this study compare closely with those reported in a wide range of experimental and field data. The appearance of high-TiO 2 kaersutitic hornblendes in the tholeities at 1000° C, P H2O = 5 kb on the QFM buffer implies that the restricted occurence of kaersutite in nature (where it is associated only with mafic to intermediate alkalic rocks) is controlled by volatile content (H 2 O , F 2 )rather than by differences in condensed bulk composition.

Journal of Petrology↗