Delamination and recycling of Archaean crust caused by gravitational instabilities

Mantle temperatures during the Archaean eon were higher than today. As a consequence, the primary crust formed at the time is thought to have been extensive, thick and magnesium rich, and underlain by a highly residual mantle1. However, the preserved volume of this crust today is low, implying that much of it was recycled back into the mantle2. Furthermore, Archaean crust exposed today is composed mostly of tonalite–trondhjemite–granodiorite, indicative of a hydrated, low-magnesium basalt source3, suggesting that they were not directly generated from a magnesium-rich primary crust. Here we present thermodynamic calculations that indicate that the stable mineral assemblages expected to form at the base of a 45-km-thick, fully hydrated and anhydrous magnesium-rich crust are denser than the underlying, complementary residual mantle. We use two-dimensional geodynamic models to show that the base of magmatically over-thickened magnesium-rich crust, whether fully hydrated or anhydrous, would have been gravitationally unstable at mantle temperatures greater than 1,500–1,550?°C. The dense crust would drip down into the mantle, generating a return flow of asthenospheric mantle that melts to create more primary crust. Continued melting of over-thickened and dripping magnesium-rich crust, combined with fractionation of primary magmas, may have produced the hydrated magnesium-poor basalts necessary to source tonalite–trondhjemite–granodiorite melts. The residues of these processes, with an ultramafic composition, must now reside in the mantle

Innovation Exposition: Advanced Research Course in Psychology (PSY 390)

The innovative Advanced Research course was designed in the early 1980s, well before the pedagogical approach of enquiry-based instruction was widely championed in the late 1990s to early 2000s (National Science Educational Standards, 1996; National Research Council, 2000). Enquiry-based instruction entails “learning through doing” and is a method of teaching and learning based on self-directed enquiry (EBL) or research (RBL) by the student (University of Manchester, 2007; University of Reading, n.d.). This course integrates a research experience for students in the psychology curriculum that reflects a cutting edge approach to teaching psychology. The “lone-wolf” model of science is outdated and one of the primary “opportunities” of today’s best practices in scientific discovery is the collaborative research model. The course provides students with critical pre-professional experiences and the research outcomes are presented at regional, national, and international professional venues

The 'Ins' and 'Outs' of the Bushveld Complex Upper Zone

This dissertation is an investigation into the geochemical and geodynamic evolution of the Upper Zone of the Bushveld Complex. The Bushveld Complex is one of the few large layered intrusions in which the entire cumulate stratigraphy is preserved and well-exposed from its base to its roof. Despite this unique feature, relatively little is known about the nature of magmatic differentiation in the uppermost portions of the Bushveld. As a first order, I quantify the chemical composition of the preserved stratigraphy (i.e. the bulk composition) from the geochemical base of the Upper Zone (the Pyroxenite Marker) to the contact with the roof. On the basis of major element modeling and trace element equilibria I show that the bulk composition is not representative of the original magma composition, and therefore some magma must be missing. I propose that the Rooiberg Group lavas and/or Rashoop granophyres, which make up the immediate roof of the intrusion, represent the missing magma. A further test of the magma-loss hypothesis comes from the trace element contents of apatites in the uppermost 625 m of the Upper Zone stratigraphy. Comparison of the equilibrium liquid compositions calculated from these apatites with the Rooiberg and/or Rashoop roof rocks shows that they are a geochemical match. My results also indicate a role for large-scale (>625 m) liquid immiscibility at the top of the Bushveld. This is the first documented evidence for liquid immiscibility based on the compositions of mineral phases, not melt inclusions; and it is the first quantitative evidence for large-scale immiscibility in the Bushveld Complex. Quantification of the parent magma composition at the Pyroxenite Marker allows me to not only estimate the `outputs' from the magma chamber, but also to constrain the `inputs'. A geochemical record of magma input and mixing is recorded in the cumulate stratigraphy for approximately 350 m below the Pyroxenite Marker. Using the evolution in mineral compositions I calculate the composition and proportion of incoming magma to the Upper Zone, as well as the style of input. The composition of the incoming magma is then compared to other known pulses of magma into the Bushveld Complex in order to put constraints on the source contributions and formation dynamics of the intrusion as a whole

Development of a model for marburgvirus based on severe-combined immunodeficiency mice

The filoviruses, Ebola (EBOV) and Marburg (MARV), cause a lethal hemorrhagic fever. Human isolates of MARV are not lethal to immmunocompetent adult mice and, to date, there are no reports of a mouse-adapted MARV model. Previously, a uniformly lethal EBOV-Zaire mouse-adapted virus was developed by performing 9 sequential passages in progressively older mice (suckling to adult). Evaluation of this model identified many similarities between infection in mice and nonhuman primates, including viral tropism for antigen-presenting cells, high viral titers in the spleen and liver, and an equivalent mean time to death. Existence of the EBOV mouse model has increased our understanding of host responses to filovirus infections and likely has accelerated the development of countermeasures, as it is one of the only hemorrhagic fever viruses that has multiple candidate vaccines and therapeutics. Here, we demonstrate that serially passaging liver homogenates from MARV-infected severe combined immunodeficient (scid) mice was highly successful in reducing the time to death in scid mice from 50–70 days to 7–10 days after MARV-Ci67, -Musoke, or -Ravn challenge. We performed serial sampling studies to characterize the pathology of these scid mouse-adapted MARV strains. These scid mouse-adapted MARV models appear to have many similar properties as the MARV models previously developed in guinea pigs and nonhuman primates. Also, as shown here, the scid-adapted MARV mouse models can be used to evaluate the efficacy of candidate antiviral therapeutic molecules, such as phosphorodiamidate morpholino oligomers or antibodies

Oxygen Isotope Trajectories of Crystallizing Melts: Insights from Modeling and the Plutonic Record

Elevated oxygen isotope values in igneous rocks are often used to fingerprint supracrustal alteration or assimilation of material that once resided near the surface of the earth. The δ^(18)O value of a melt, however, can also increase through closed-system fractional crystallization. In order to quantify the change in melt δ^(18)O due to crystallization, we develop a detailed closed-system fractional crystallization mass balance model and apply it to six experimentally- and naturally-determined liquid lines of descent (LLDs), which cover nearly complete crystallization intervals (melt fractions of 1 to <0.1). The studied LLDs vary from anhydrous tholeiitic basalts to hydrous high-K and calc-alkaline basalts and are characterized by distinct melt temperature-SiO_2 trajectories, as well as, crystallizing phase relationships. Our model results demonstrate that melt fraction-temperature-SiO_2 relationships of crystallizing melts, which are strongly a function of magmatic water content, will control the specific δ^(18)O path of a crystallizing melt. Hydrous melts, typical of subduction zones, undergo larger increases in δ^(18)O during early stages of crystallization due to their lower magmatic temperatures, greater initial increases in SiO_2 content, and high temperature stability of low δ^(18)O phases, such as oxides, amphibole, and anorthitic plagioclase (versus albite). Conversely, relatively dry, tholeiitic melts only experience significant increases in δ^(18)O at degrees of crystallization greater than 80%. Total calculated increases in melt δ^(18)O of 1.0 to 1.5‰ can be attributed to crystallization from ∼50 to 70 wt.% SiO_2 for modeled closed-system crystallizing melt compositions. As an example application, we compare our closed system model results to oxygen isotope mineral data from two natural plutonic sequences, a relatively dry, tholeiitic sequence from the Upper and Upper Main Zones (UUMZ) of the Bushveld Complex (South Africa) and a high-K, hydrous sequence from the arc-related Dariv Igneous Complex (Mongolia). These two sequences were chosen as their major and trace element compositions appear to have been predominantly controlled by closed-system fractional crystallization and their LLDs have been modeled in detail. We calculated equilibrium melt δ^(18)O values using the measured mineral δ^(18)O values and calculated mineral-melt fractionation factors. Increases of 2-3‰ and 1-1.5‰ in the equilibrium melts are observed for the Dariv Igneous Complex and the UUMZ of the Bushveld Complex, respectively. Closed-system fractional crystallization model results reproduce the 1‰ increase observed in the equilibrium melt δ^(18)O for the Bushveld UUMZ, whereas for the Dariv Igneous Complex assimilation of high δ^(18)O material is necessary to account for the increase in melt δ^(18)O values. Assimilation of evolved supracrustal material is also confirmed with Sr and Nd isotope analyses of clinopyroxene from the sequence. Beginning with a range of mantle-derived basalt δ^(18)O values of 5.7‰ (“pristine” mantle) to ∼7.0‰ (heavily subduction-influenced mantle), our model results demonstrated that high-silica melts (i.e. granites) with δ^(18)O of up to 8.5‰ can be produced through fractional crystallization alone. Lastly, we model the zircon-melt δ^(18)O fractionations of different LLDs, emphasizing their dependence on the specific SiO_2-T relationships of a given crystallizing melt. Wet, relatively cool granitic melts will have larger zircon-melt fractionations, potentially by ∼1.5‰, compared to hot, dry granites. Therefore, it is critical to constrain zircon-melt fractionations specific to a system of interest when using zircon δ^(18)O values to calculate melt δ^(18)O

Constraining fault friction in oceanic lithosphere using the dip angles of newly-formed faults at outer rises

We investigate the mechanical properties of the oceanic lithosphere using earthquake focal mechanisms from subduction zone outer rises. We study regions where faulting oblique to the pre-existing mid-ocean ridge fabric implies the formation of new faults. The nodal-plane dips of dip-slip earthquakes on these faults are dominantly in the range 30–60°, with a strong peak concentrated around 45°. This distribution is inconsistent with the pattern that would result from high coefficients of friction (e.g. 0.6, equivalent to normal faults forming at 60° and thrust faults at 30°). We instead suggest that the observed distribution of dips implies that faults in the oceanic lithosphere have a low coefficient of friction, due to either low-friction clay minerals formed by hydrothermal alteration at the ridge, or due to an intrinsic level of friction that is lower than that suggested by laboratory studies

Forgiveness Increases Meaning in Life

Close relationships are a source of meaning in life. Interpersonal offenses can disrupt one\u27s sense of meaning within close relationships. To restore a sense of meaning, people may employ relational repair strategies such as forgiveness. We hypothesized that forgiveness is a meaning-making mechanism because it helps repair relationships, thus restoring the positive effects of relationships on meaning. Study 1 (N = 491) revealed that dispositional forgiveness and the degree of forgiveness following an offense were positively related to meaning in life. Study 2 (N = 210), a 6-month longitudinal study of romantic couples, revealed that participants who regularly forgave their partner reported increased meaning in life over time. In addition, forgiveness helped recover lost meaning among those participants reporting more frequent partner offenses. These results provide initial evidence that forgiveness recovers a sense of meaning in life after interpersonal offenses

Worldview Conflict in Daily Life

Building on laboratory- and survey-based research probing the psychology of ideology and the experience of worldview conflict, we examined the association between worldview conflict and emotional reactions, psychological well-being, humanity esteem, and political ideology in everyday life using experience sampling. In three combined samples (total N = 328), experiencing disagreement compared to agreement was associated with experiencing more other-condemning emotions, less well-being, and less humanity esteem. There were no clear associations between experiencing disagreement and experiencing self-conscious emotions, positive emotions, and mental stress. None of the relationships were moderated by political ideology. These results both replicate and challenge findings from laboratory- and survey-based research, and we discuss possible reasons for the discrepancies. Experience sampling methods can help researchers get a glimpse into everyday worldview conflict