Michael O. Garcia

The Amount of Recycled Crust in Sources of Mantle-Derived Melts

One proposed strategy for controlling the transmission of insect-borne pathogens uses a drive mechanism to ensure the rapid spread of transgenes conferring disease refractoriness throughout wild populations. Here, we report the creation of maternal-effect selfish genetic elements in Drosophila that drive population replacement and are resistant to recombination-mediated dissociation of drive and disease refractoriness functions. These selfish elements use microRNA-mediated silencing of a maternally expressed gene essential for embryogenesis, which is coupled with early zygotic expression of a rescuing transgene.The phosphoinositide phosphatase PTEN is mutated in many human cancers. Although the role of PTEN has been studied extensively, the relative contributions of its numerous potential downstream effectors to deregulated growth and tumorigenesis remain uncertain. We provide genetic evidence in Drosophila melanogaster for the paramount importance of the protein kinase Akt [also called protein kinase B (PKB)] in mediating the effects of increased phosphatidylinositol 3,4,5-trisphosphate (PIP3) concentrations that are caused by the loss of PTEN function. A mutation in the pleckstrin homology (PH) domain of Akt that reduces its affinity for PIP3 sufficed to rescue the lethality of flies devoid of PTEN activity. Thus, Akt appears to be the only critical target activated by increased PIP3 concentrations in Drosophila.Using genomic and mass spectrometry-based proteomic methods, we evaluated gene expression, identified key activities, and examined partitioning of metabolic functions in a natural acid mine drainage (AMD) microbial biofilm community. We detected 2033 proteins from the five most abundant species in the biofilm, including 48% of the predicted proteins from the dominant biofilm organism, Leptospirillum group II. Proteins involved in protein refolding and response to oxidative stress appeared to be highly expressed, which suggests that damage to biomolecules is a key challenge for survival. We validated and estimated the relative abundance and cellular localization of 357 unique and 215 conserved novel proteins and determined that one abundant novel protein is a cytochrome central to iron oxidation and AMD formation.

Primitive magmas and source characteristics of the Hawaiian plume: petrology and geochemistry of shield picrites

A suite of tholeiitic picrites from eight of the younger (<2 Ma) Hawaiian shield volcanoes provides new information about the compositions of primitive magmas and source components in the Hawaiian plume. Olivine and bulk rock compositions show that parental melts at Hawaiian volcanoes have at least 13–17% MgO and ∼10% Al2O3. The picrites have bulk compositions ranging from 14 to 30% MgO, and although most of these lavas have accumulated olivine + spinel, several have compositions that may approximate primitive melts. Olivine and spinel compositions show that the phenocrysts are closely related to the melt fraction of these lavas and are not accidental xenocrysts. Diverse isotopic compositions (Pb, Os, Sr, Nd) of these picrites require multiple sources in the Hawaiian plume, but key trace element characteristics (La, Nb abundances normalized to 16% MgO, Sm/Nd, Lu/Hf, La/Yb, Zr/Nb) are consistent with variable degrees of melting of a common, garnet-bearing source for all of the volcanoes except Koolau. The trace element composition of this Hawaiian pyrolite plume source can be modelled as an incipiently depleted, nearly primitive mantle that has lost a very small melt fraction, but a more complex origin may be more realistic. The Koolau picrites are exceptional in having anomalously low Nb and Ti contents, and high Zr/Nb ratios that fall off the melting arrays defined by the other picrites, indicating a distinctive source component that is also expressed in major element and isotopic compositions. The nearly constant Sr/Pb, Sr/Y, and Ba/Th ratios of these isotopically variable picrites are inconsistent with formation of the plume source either by bulk recycling of oceanic crust into the mantle, or by addition of dacitic melts from entrained eclogite to plume-derived basaltic magmas. Alternatively, the Hawaiian plume may consist of variably depleted mantle that was enriched by small-degree melts, possibly during subduction or entrainment of lithospheric mantle. Radiogenic 186Os/188Os isotopic compositions of these picrites are consistent with transport of this material to the deep lower mantle and addition of a small amount of outer core to the plume source.

Geochemical characteristics of Koolau Volcano: Implications of intershield geochemical differences among Hawaiian volcanoes

The voluminous shields of Hawaiian volcanoes are dominantly composed of tholeiitic basalts, but there are important intershield geochemical differences. The subaerial lavas forming the ~2–3 Ma Koolau shield have several extreme characteristics: relatively high abundances of SiO2, low abundances of total iron and CaO, and high ratios of LaNb and SrNb. In addition, they range to near bulk-earth strontium, neodymium, and lead isotopic ratios. Although postmagmatic alteration has significantly affected the compositions of some Koolau lavas (decreases in SiO2, K2O, and rubidium contents, increases in total iron and in unusual cases, increases in yttrium and REE abundances), the geochemical charac teristics of unaltered Koolau lavas reflect a distinctive primary magma composition. Within a stratigraphic sequence of lavas, Koolau lavas vary significantly in incompatible element abundance and isotopic ratios, but these variations are not systematic with eruption age, and they are smaller than the differences between Hawaiian shields. Intershield differences in some incompatible element abundance ratios, LaNb and SrNb, are correlated with intershield differences in isotopic ratios, thereby indicating that each shield formed from a compositionally distinct source. However, other intershield compositional differences are not correlated with differences in radiogenic isotope ratios. Some of these compositional differences probably reflect variations in the melting process; e.g., inverse correlations between SiO2 and total iron contents may reflect differences in the pressure of melt segregation, differences in abundances of incompatible elements may reflect variations in mean degree of melting, and variations in ratios like SmNd may reflect the presence of residual garnet. Each shield appears to reflect a unique combination of source components and variables, such as extent of melting and pressure of melt segregation. Consequently, the intershield geochemical differences have important implications for plume structure. Either a relatively large plume has a spatially systematic distribution of geochemical heterogeneities which are sampled by the overlying shields, or each shield is derived from a small radius (<20 km) conduit composed of geochemically distinct diapirs or solitary waves.

Quantitative analysis of trace element abundances in glasses and minerals: a comparison of laser ablation inductively coupled plasma mass spectrometry, solution inductively coupled plasma mass spectrometry, proton microprobe and electron microprobe data

Many geological, environmental and industrial applications can be enhanced through integrated microbeam and bulk geochemical determinations of major and trace element concentrations. Advantages ofin situ microanalysis include minimal sample preparation, low blanks, information about the spatial distribution of compositional characteristics and the ability to avoid microscopic inclusions of foreign material. In this paper we compare trace element data obtained by laser ablation ICP-MS, solution ICP-MS, electron microprobe analysis and proton microprobe analysis for a variety of silicate glasses and minerals. New determinations for 36 trace elements in BCR-2G, a microbeam glass standard, are presented. Results obtained by the various microbeam and solution methods agree well for concentrations ranging over several orders of magnitude. Replicate analyses of BCR-2G demonstrate an analytical precision of 2–8% relative (1σ) for all elements by laser ablation ICP-MS and ≤3% by solution ICP-MS, except for Li (5%). These data emphasize the utility of laser ablation ICP-MS as a quantitative microbeam technique capable of rapid, precise determinations of sub-ppm trace element abundances in a variety of targets.

The evolution of Mauna Kea Volcano, Hawaii: Petrogenesis of tholeiitic and alkalic basalts

Mauna Kea Volcano has three exposed rock units. Submarine shield-building tholeiites form the oldest unit. Subaerial, interbedded tholeiitic and alkalic basalts form the intermediate age unit (70–240 Ka), and they are partially covered by evolved alkalic lavas, hawaiites and mugearites (4–66 Ka). In contrast to other Hawaiian volcanoes, such as Haleakala and Kauai, lavas from Mauna Kea do not define systematic temporal variations in Pb, Sr or Nd isotopic ratios. However with decreasing age the tholeiitic basalts are increasingly enriched in incompatible elements; therefore the shield and postshield tholeiites were derived from compositionally distinct parental magmas. Submarine shield lavas from the east rift contain forsterite-rich olivine (up to Fo90.5) providing evidence for MgO-rich (14.4 to 17%) magmas. Postshield tholeiitic and alkalic basalts with similar isotopic ratios may have been derived from the same source composition by different degrees of partial melting. If a compositionally and isotopically homogeneous source and a batch melting model are assumed, inversion of incompatible element abundance data for the postshield basalts requires low degrees (<2%) of melting of a garnet Iherzolite source which had near-chondritic abundances of heavy rare-earth elements (REE) but less than chondritic abundances of highly incompatible elements such as Ba, Nb and light REE. As the volcano migrated away from the hotspot, eruption rates decreased enabling high Fe-Ti basalts to form by fractional crystallization in shallow crustal magma chambers. The associated phenocryst-rich, high-MgO postshield lavas (picrites and ankaramites) are products of phenocryst accumulation. Eventually basaltic eruptions ceased, and the youngest Mauna Kea lavas are exclusively hawaiites and mugearites which formed from alkalic basalt parental magmas by clinopyroxene-dominated fractionation at lower crustal pressures.

Volatiles in submarine volcanic rocks from the Mariana Island arc and trough

High temperature mass spectrometric analyses of glasses from quenched pillow rims of andesites dredged from 1170 m water depth in the northern portion of the Mariana Island arc indicate substantially less H2O (~ 1 wt.%) and more CO2 (~ 0.24 wt.%) than previously reported for volcanic arc rocks. Glass-vapor inclusions within plagioclase phenocrysts from quenched rims have CO2H2O ratios of 1:1. These results are similar to analyses of basaltic samples from the Mariana Trough (a back-arc basin). Generally, F and Cl contents are higher and S lower in the arc rocks compared to the samples from the back-arc basin. These results favor models for the production of island arc magmas which involve melting of the subducted slab, rather than just melting of the overlying mantle wedge because of the high volatile content needed to produce island arc magmas from peridotite (10–15 wt.%). The trough samples, although similar in non-volatile composition to mid-ocean ridge rocks, have much higher H2O. somewhat higher CO2 and lower S contents. Either near surface addition of voiatiles has enriched the magmas or H2O must be a more important component in the generation and evolution of back-arc basin lavas than in the genesis of mid-ocean ridge basalts.

Generation of Hawaiian post-erosional lavas by melting of a mixed lherzolite/pyroxenite source

Abstract Melting of mafic veins in a marble-cake mantle may play an important role in generating isotopic and chemical heterogeneities in mid-ocean ridge and ocean island basalts. Mafic veins have lower solidi than mantle peridotite and will be preferentially sampled during partial melting, particularly at low melt fractions. However, the abundance of mafic components in the mantle or their role during melt generation has been difficult to quantify because most isotopic systems (e.g. Rb–Sr, Sm–Nd, U–Th–Pb) are not diagnostic of the presence or absence of mafic components. The compatible behavior of Os during mantle melting combined with the incompatible behavior of Re makes the Re–Os isotopic system uniquely well suited for distinguishing mafic and ultramafic contributions to melt generation. Almost all peridotites have low 187Os/188Os (e.g. chondritic to subchondritic). In contrast, mafic rocks have much higher Re/Os than peridotites, which results in the rapid ingrowth of 187Os and the development of large isotopic contrasts between mafic and ultramafic components within the mantle. In this paper, we show that Os-isotopes in Hawaiian post-erosional lavas extend to more radiogenic values than are found in Hawaiian lherzolites, abyssal peridotites or most other ultramafic samples. Os-isotopes are not correlated with other isotopic tracers, in contrast with plume-derived Hawaiian shield-stage lavas. The lack of correlation between Os-isotopes and Sr-, Nd- or Pb-isotopes and the more ‘depleted’ or MORB-like Sr–Nd isotopic signature of the post-erosional lavas relative to other Hawaiian lavas precludes significant melt input from the Hawaiian plume. However, Os-isotopes are correlated with major and trace elements. Lavas with more radiogenic Os-isotope compositions have higher silica and alumina and lower calcium and incompatible trace element abundances than lavas with less radiogenic Os-isotopes. These correlations result from mixing of pyroxenite- and peridotite-derived melts, both likely derived from the ∼100 Ma Pacific lithospheric mantle.

The tholeiite to alkalic basalt transition at Haleakala Volcano, Maui, Hawaii

Previous studies of alkalic lavas erupted during the waning growth stages (<0.9 Ma to present) of Haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios. These geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components. We studied lavas from a 250-m-thick stratigraphic sequence in Honomanu Gulch that includes the oldest (∼1.1 Ma) subaerial basalts exposed at Haleakaka. The lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic (Sr, Nd, Pb) and incompatible element abundance ratios (e.g., Nb/La, La/Ce, La/Sr, Hf/Sm, Ti/Eu). These lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous, clinopyroxene-rich, garnet lherzolite source. The intercalated tholeiitic and alkalic Honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume, and we infer that the tholeiitic lavas reflect a melting range of ∼10% to 15%, while the intercalated alkalic lavas reflect a range of ∼6.5% to 8% melting. However, within the uppermost 50 m of section. 87Sr/86Sr decreases from 0.70371 to 0.70328 as eruption age decreased from ∼0.97 Ma to 0.78 Ma. We infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at ∼0.93 Ma, the mixing proportions of source components changed with a MORB-related mantle component becoming increasingly important as eruption age decreased.

Rhenium and platinum group element abundances correlated with mantle source components in Hawaiian picrites: sulphides in the plume

Core addition and crustal recycling models that seek to explain the radiogenic Os isotopic compositions of primitive Hawaii tholeiites predict distinctive geochemical consequences for chalcophile and siderophile element abundances in the mantle plume. To test these models and to improve our understanding of compositional variability in the Hawaiian plume, the platinum group element (PGE) and Re contents of primitive shield picrites from several Hawaiian volcanoes were measured. PGE abundances span a large range, from similar to MORB for a picrite from Koolau, to compositions similar to those of basaltic komatiites for picrites from Kilauea and Loihi. Re concentrations range from 0.25 to 0.95 ng/g and with a mean of 0.73 ng/g, higher than previously compiled global averages for ocean island basalts (OIB) (0.38 ng/g) and closer to average MORB (0.98 ng/g) than previously recognised. Some subaerial tholeiites, notably from Kilauea and Mauna Kea, have anomalously low Re abundances and high Cu/Re ratios, possibly reflecting Re loss upon eruption or during degassing of shallow magma chambers. These data show that the PGE and primary Re contents of primitive Hawaiian picrites are well correlated with isotopic compositions of these lavas, linking the PGE and Re characteristics directly with source features of the mantle plume. However, mixing models that describe the isotopic effects of core addition and crustal recycling do not account for the PGE and Re abundances. The range of PGE and Re contents in these lavas does not appear to reflect abundance variations in the plume components, but some aspect of the melting process that is linked to source characteristics of the plume. One possibility is that the PGE and Re characteristics of Hawaiian tholeiites may reflect variable amounts or compositions of residual sulphide during melting. In this scenario, the high PGE and Re contents of Kilauea and Loihi picrites may be indicating a relatively small amount of residual sulphide during melting, whereas the low PGE and Re contents of Koolau primitive magmas may be indicating greater amounts of residual sulphide in the plume. The systematic compositional variations of PGE and Re in primitive tholeiites must be accounted for by any model for the origin of the Hawaiian plume.

An evaluation of temporal geochemical evolution of Loihi Summit Lavas: Results from Alvin submersible dives

Stratigraphically controlled sequences of in situ lavas were collected from Loihi Seamount using the Alvin submersible to evaluate the volcanos temporal geochemical evolution. Three sections with up to 370 m of relief were sampled from the two pit craters at the summit of Loihi. All of the analyses were done on glass separates. Our results indicate that tholeiitic and alkalic volcanism at the summit of Loihi has been coeval. The tholeiitic and alkalic lavas have similar incompatible element patterns and O, Pb, Sr, and Nd isotope ratios but are distinct in some incompatible element ratios. These results are consistent with the different Loihi rock types being derived by variable degrees of melting from a common source. The crossing and light-rare-earth-enriched rare earth element patterns and variable Sc/Yb ratios of the tholeiites indicate that their source was a garnet lherzolite. The relatively low δ18O values (∼4.9 ‰) for Loihi lavas are interpreted to be characteristic of the Hawaiian plume.