Petrography and petrology of the Hawaii Scientific Drilling Project lavas: Inferences from olivine phenocryst abundances and compositions

The Mauna Loa (ML) and Mauna Kea (MK) lavas recovered by the Hawaii Scientific Drilling Project (HSDP) include aphyric to highly olivine-phyric basalts. The average olivine phenocryst abundance in the reference suite of ML flows is 14.5 vol % (vesicle-free and weighted by the flow thickness), while the average abundances of olivine in the reference suites of the MK alkalic and tholeiitic basalts are 1.1 and 14.0 vol %, respectively. Plagioclase and augite phenocrysts are rare in the ML and MK tholeiites, but the MK alkalic basalts can have up to 4 vol % plagioclase phenocrysts. Strained olivine grains, thought to represent disaggregated dunite xenoliths from the cumulate pile within the magma chamber(s), are ubiquitous in the drill core lavas. These deformed grains can comprise up to 50 % of the modal olivine in a given rock. Olivine core compositions in the lavas span forsterite contents of 80.4–90.7 (median 88.8, ML tholeiites), 75.8–86.6 (median 85.8, MK alkalic basalts), and 76.3–90.5 (median 88.0 mol %, MK tholeiites). Olivines with core compositions in the range Fo_(89–90.5) are present in tholeiitic lavas with a wide range of whole-rock MgO contents (9–30 wt %). Strained and unstrained olivines completely overlap in composition as do the compositions of spinels (100*Cr/(Cr+Al) ∼59–72; Mg# = 100*Mg/(Mg+Fe^(2+)) ∼40–66) present as inclusions in the olivine phenocrysts. The presence of Fo_(90.5) olivine in the HSDP lavas requires magmas with ∼16 wt % MgO in the ML and MK plumbing systems. Rare dunite xenoliths are also present in the drill core lavas. While compositionally homogeneous within a given xenolith, the six xenoliths contain olivines that span a wide range of forsterite contents (78.3–89.2 mol %). Spinels in these xenoliths are chrome-rich, have Mg# between 31 and 66, and define two populations on the basis of TiO_2 contents. Whole-rock compositions for the ML and MK tholeiites define olivine control lines on MgO-oxide diagrams, and the relationship between whole-rock MgO and olivine phenocryst abundance in these lavas suggests that the lavas with >12 wt % MgO have accumulated olivine. Comparing the weighted bulk composition of all of the MK tholeiites in the drill core with a calculated parental magma suggests that, on average, the MK tholeiites entrained most of the olivine phenocrysts that crystallized from their parental liquids. Although deformed olivines in Hawaiian lavas are widely thought to represent disaggregated dunite xenoliths, none of the majoror minor-element data on the strained or unstrained olivine phenocrysts suggest that the strained olivines in the HSDP lavas are exotic. We suggest that most of the olivine phenocrysts in a given flow, whether strained or unstrained, are closely related to the evolved liquid that now forms the groundmass. This is consistent with observed correlations between isotopic systems measured on olivine separates (e.g., O, He) and isotopic systems dominated by groundmass (e.g., Nd, Pb)

Volatiles in glasses from the HSDP2 drill core

H2O, CO2, S, Cl, and F concentrations are reported for 556 glasses from the submarine section of the 1999 phase of HSDP drilling in Hilo, Hawaii, providing a high-resolution record of magmatic volatiles over ~200 kyr of a Hawaiian volcano's lifetime. Glasses range from undegassed to having lost significant volatiles at near-atmospheric pressure. Nearly all hyaloclastite glasses are degassed, compatible with formation from subaerial lavas that fragmented on entering the ocean and were transported by gravity flows down the volcano flank. Most pillows are undegassed, indicating submarine eruption. The shallowest pillows and most massive lavas are degassed, suggesting formation by subaerial flows that penetrated the shoreline and flowed some distance under water. Some pillow rim glasses have H2O and S contents indicating degassing but elevated CO2 contents that correlate with depth in the core; these tend to be more fractionated and could have formed by mixing of degassed, fractionated magmas with undegassed magmas during magma chamber overturn or by resorption of rising CO2-rich bubbles by degassed magmas. Intrusive glasses are undegassed and have CO2 contents similar to adjacent pillows, indicating intrusion shallow in the volcanic edifice. Cl correlates weakly with H2O and S, suggesting loss during low-pressure degassing, although most samples appear contaminated by seawater-derived components. F behaves as an involatile incompatible element. Fractionation trends were modeled using MELTS. Degassed glasses require fractionation at pH2O ≈ 5–10 bars. Undegassed low-SiO2 glasses require fractionation at pH2O ≈ 50 bars. Undegassed and partially degassed high-SiO2 glasses can be modeled by coupled crystallization and degassing. Eruption depths of undegassed pillows can be calculated from their volatile contents assuming vapor saturation. The amount of subsidence can be determined from the difference between this depth and the sample's depth in the core. Assuming subsidence at 2.5 mm/y, the amount of subsidence suggests ages of ~500 ka for samples from the lower 750 m of the core, consistent with radiometric ages. H2O contents of undegassed low-SiO2 HSDP2 glasses are systematically higher than those of high-SiO2 glasses, and their H2O/K2O and H2O/Ce ratios are higher than typical tholeiitic pillow rim glasses from Hawaiian volcanoes

Field assessment of sediment trap efficiency under varying flow conditions

Knowledge of the collection efficiency of sediment traps, particularly under conditions of varying current speed, is presently more a matter of hope than confidence. We report here on a field experiment designed to determine, for a particular trap geometry, the effect of current speed and particle fall velocity on the collection efficiency of a moored trap relative to the presumably unbiased efficiency of an identical drifting trap. The experiment was performed in a deep estuarine tidal passage where a smoothly varying unidirectional flow and a spatially homogenous particle population mimicked laboratory flume conditions. A multiple-sample sediment trap integrated to a current meter partitioned the mass flux collected by the moored trap into one of four chambers according to the following speed intervals: \u3c12, 12–\u3c30, 30–\u3c50, and ≥50cm/s. The magnitude and particle characteristics of the flux collected at \u3c12 cm/s were indistinguishable from those simultaneously collected by drifting traps. At higher speeds, the relative efficiency of the moored trap ranged between 1% and 24% and the mean size and density of the trapped particles increased. These results support predictions based on laboratory studies that collection efficiency decreases with an increase in the trap Reynolds number or a decrease in particle fall velocity. The study demonstrates that consideration must be given to scaling both trap diameter and aspect ratio according to the expected flow conditions, and that knowledge of flow conditions at the trap mouth is necessary to properly interpret the flux data

Supersymmetric Open Wilson Lines

In this paper we study Open Wilson Lines (OWL's) in the context of two Supersymmetric Yang Mills theories. First we consider four dimensional N=2 Supersymmetric Yang Mills Theory with hypermultiplets transforming in the fundamental representation of the gauge group, and find supersymmetric OWL's only in the superconformal versions of these theories. We then consider four dimensional N=4 SYM coupled to a three dimensional defect hypermultiplet. Here there is a semi-circular supersymmetric OWL, which is related to the ray by a conformal transformation. We perform a perturbative calculation of the operators in both theories, and discuss using localization to compute them non-perturbatively.Comment: 26 pages, 3 figure

The Temperature and Pressure Dependence of Nickel Partitioning between Olivine and Silicate Melt

We measured Ni partitioning between olivine and melt, D^(ol/liq)_(Ni), in experiments on mid-ocean ridge basalt (MORB) encapsulated in olivine at pressures from 1 atm to 3·0 GPa and temperatures from 1400 to 1550°C. We present a series of experiments where the temperature (T) at each pressure (P) was selected so that the liquid composition remained approximately constant over the entire P–T range. This approach allowed us to investigate the effects of T and P on D^(ol/liq)_(Ni), independent of substantial changes in liquid composition. Our experiments show that for a liquid with ∼18 wt% MgO, D^(ol/liq)_(Ni) decreases from 5·0 to 3·8 as the temperature increases from 1400 to 1550°C. Fitting our experimental results and literature data to thermodynamic expressions for D^(ol/liq)_(Ni) as a function of both temperature and liquid composition shows that the small variations in liquid composition in our experiments account for little of the observed variation of D^(ol/liq)_(Ni). Because the changes in volume and heat capacity of the exchange reaction MgSi_(0-5)O^(ol)_2 + D^(ol/liq)_(Ni) ↔ NiSi_(0-5)O^(ol)_2 + MgO^(liq) are small, D^(molar)_(Ni), the Ni partition coefficient on a molar basis, is well described by In(D^(molar)_(Ni))=-^(Δ_rHo_(T_(ref)),P_(ref)/_(RT) + ^Δ_rSo_(T_(ref),P_(ref))/_R - In (X^(liq)_(MgO)/X^(ol)_(MgSi)_(0-5)O_2) with Δ_rH^o_T_(ref),_P_(ref)/_R = 4375 K and Δ_rSo_T_(ref),_P_(ref)/_R = –2·023 for our data (Δ_rH^o_T_(ref),_P_(ref)/_R = 4338 K and Δ_rSo_T_(ref),_P_(ref)/_R = –1·956 for our experiments combined with a compilation of literature data). This expression is easy to use and applicable to a wide range of pressures, temperatures, and phase compositions. Based on our results and data from the literature, the temperature dependence of D^(ol/liq)_(Ni) leads to the prediction that when a deep partial melt from a peridotitic mantle source is brought to low pressure and cooled, the first Mg-rich olivines to crystallize can have significantly higher NiO contents than those in the residual source from which the melt was extracted. This enrichment in Ni is driven by the difference between the temperature of low-pressure crystallization and the temperature of melt extraction from the residue. The average observed enrichment of Ni in forsteritic olivine phenocrysts from Hawaii—relative to the typical olivines from mantle peridotites—is consistent with a simple scenario of high-temperature partial melting of an olivine-bearing source at the base of the lithosphere followed by low-temperature crystallization of olivine. The most extreme enrichments of Ni in Hawaiian olivine phenocrysts and the lower Ni contents of some olivines can also be explained by the known variability of Ni contents of olivines from mantle peridotites via the same simple scenario. Although we cannot rule out alternative hypotheses for producing the high-Ni olivines observed in Hawaii and elsewhere, these processes or materials are unnecessary to account for NiO enrichments in olivine. The absolute temperature, in addition to the difference between the temperature of melt segregation from the residue and the temperature of low-pressure crystallization, is a significant factor in determining the degree of Ni enrichment in olivine phenocrysts relative to the olivines in the mantle source. The moderate Ni enrichment observed in most komatiitic olivines compared with those of Hawaii may result from the higher absolute temperatures required to generate MgO-rich komatiitic melts. Observed NiO enrichments in early crystallizing komatiitic olivine are consistent with their high temperatures of crystallization and with a deep origin for the komatiite parental melts

Fe-Mg Partitioning between Olivine and High-magnesian Melts and the Nature of Hawaiian Parental Liquids

We conducted 1 atm experiments on a synthetic Hawaiian picrite at fO_2 values ranging from the quartz–fayalite–magnetite (QFM) buffer to air and temperatures ranging from 1302 to 1600°C. Along the QFM buffer, olivine is the liquidus phase at ~1540°C and small amounts of spinel (< 0·2 wt %) are present in experiments conducted at and below 1350°C. The olivine becomes progressively more ferrous with decreasing temperature [Fo_(92·3) to Fo_(87·3), where Fo = 100 × Mg/(Mg + Fe), atomic]; compositions of coexisting liquids reflect the mode and composition of the olivine with concentrations of SiO_2, TiO_2, Al_(2)O_3, and CaO increasing monotonically with decreasing temperature, those of NiO and MgO decreasing, and FeO^* (all Fe as FeO) remaining roughly constant. An empirical relationship based on our data, T(°C) = 19·2 × (MgO in liquid, wt %) + 1048, provides a semi-quantitative geothermometer applicable to a range of Hawaiian magma compositions. The olivine–liquid exchange coefficient, K_(D,Fe^(2+)-Mg) = (FeO/MgO)^(ol)/(FeO/MgO)^(liq), is 0·345 ± 0·009 (1σ ) for our 11 experiments. A literature database of 446 1 atm experiments conducted within 0·25 log units of the QFM buffer (QFM ± 0·25) yields a median K_(D,Fe^(2+)-Mg) of 0·34; K_(D,Fe^(2+)-Mg) values from single experiments range from 0·41 to 0·13 and are correlated with SiO_2 and alkalis in the liquid, as well as the forsterite (Fo) content of the olivine. For 78 experiments with broadly tholeiitic liquid compositions (46–52 wt % SiO_2 and ≤ 3 wt % Na_(2)O + K_(2)O) coexisting with Fo_(92–80) olivines, and run near QFM (QFM ± 0·25), K_(D,Fe^(2+)-Mg) is approximately independent of composition with a median value of 0·340 ± 0·012 (error is the mean absolute deviation of the 78 olivine–glass pairs from the database that meet these compositional criteria), a value close to the mean value of 0·343 ± 0·008 from our QFM experiments. Thus, over the composition range encompassed by Hawaiian tholeiitic lavas and their parental melts, K_(D,Fe^(2+)-Mg) ~ 0·34 and, given the redox conditions and a Fo content for the most magnesian olivine phenocrysts, a parental melt composition can be reconstructed. The calculated compositions of the parental melts are sensitive to the input parameters, decreasing by ~1 wt % MgO for every log unit increase in the selected fO_2, every 0·5 decrease in the Fo-number of the target olivine, and every 0·015 decrease in K_(D,Fe^(2+)-Mg). For plausible ranges in redox conditions and Fo-number of the most MgO-rich olivine phenocrysts, the parental liquids for Hawaiian tholeiites are highly magnesian, in the range of 19–21 wt % MgO for Kilauea, Mauna Loa and Mauna Kea

The 3D Grazing Collision of Two Black Holes

We present results for two colliding black holes (BHs), with angular momentum, spin, and unequal mass. For the first time gravitational waveforms are computed for a grazing collision from a full 3D numerical evolution. The collision can be followed through the merger to form a single BH, and through part of the ringdown period of the final BH. The apparent horizon is tracked and studied, and physical parameters, such as the mass of the final BH, are computed. The total energy radiated in gravitational waves is shown to be consistent with the total mass of the spacetime and the final BH mass. The implication of these simulations for gravitational wave astronomy is discussed.Comment: 4 pages, 7 figures, revte