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Oceanic hotspots with extreme enriched mantle radiogenic isotopic signatures—including low¹⁴³Nd/¹⁴⁴Nd indicative of subducted continental crust—are linked to plume conduits sampling the southern hemispheric mantle. However, the mechanisms responsible for concentrating subducted continental crust in the austral mantle are unknown. We show that subduction of sediments and subduction eroded material, and lower continental crust delamination, cannot generate this spatially coherent austral geochemical domain. However, continental collisions—associated with the assembly of Gondwana‐Pangea—were positioned predominantly in the southern hemisphere during the late Neoproterozoic appearance of widespread continental ultra‐high‐pressure metamorphic terranes, which marked the onset of deep subduction of upper continental crust. We propose that deep subduction of upper continental crust at ancient rifted‐passive margins during ca. 650‐300 Ma austral supercontinent assembly resulted in enhanced upper continental crust delivery into the southern hemisphere mantle. Similarly enriched mantle domains are absent in the boreal mantle plume source, for two reasons. First, continental crust subducted after 300 Ma—when the continents drifted into the northern hemisphere—has had insufficient time to return to the surface in plumes sampling the northern hemisphere mantle. Second, before the first known appearance of continental ultra‐high‐pressure rocks at 650 Ma, deep subduction of upper continental crust was uncommon, limiting its subduction into the northern (and southern) hemisphere mantle earlier in Earth history. Our model implies a recent formation of the austral enriched mantle domain, explains the geochemical dichotomy between austral and boreal plume sources, and may explain why there are twice as many austral hotspots as boreal hotspots.

 

SUMMARY Lamellar magnetism is a source of remanent magnetization in natural rocks different from common bulk magnetic moments in ferrimagnetic minerals. It has been found to be a source for a wide class of magnetic anomalies with extremely high Koenigsberger ratio. Its physical origin are uncompensated interface moments in contact layers of nanoscale ilmenite lamellae inside an hematite host, which also generate unusual low-temperature (low-T) magnetic properties, such as shifted low-T hysteresis loops due to exchange bias. The atomic-magnetic basis for the exchange bias discovered in the hematite-ilmenite system is explored in a series of papers. In this third article of the series, simple models are developed for lamellae interactions of different structures when samples are either cooled in zero-field, or field-cooled in 5 T to temperatures below the ordering temperature of ilmenite. These models are built on the low-temperature measurements described earlier in Paper II. The important observations include: (i) the effects of lamellar shapes on magnetic coupling, (ii) the high-T acquisition of lamellar magnetism and low-T acquisition of magnetization of ilmenite lamellae, (iii) the intensity of lamellar magnetism and the consequent ilmenite magnetism in populations of randomly oriented crystals, (iv) lattice-preferred orientation of the titanohematite host crystal populations and (v) the effects of magnetic domain walls in the host on hysteresis properties. Based on exemplary growth models of lamellae with different geometries and surface couplings we here provide simple models to assess and explain the different observations listed above. Already the simplified models show that the shapes of the edges of ilmenite lamellae against their hematite hosts can control the degree of low-T coupling between ilmenite, and the lamellar magnetic moments. The models also explain certain features of the low-T exchange bias in the natural samples and emphasize the role of lattice-preferred orientation upon the intensity of remanent magnetization. The inverse link between ilmenite remanence and exchange-bias shift in bimodal low-T ilmenite lamellae is related to different densities of hematite domain walls induced by the clusters of ilmenite lamellae. 

With support from NSF Scholarships in Science, Technology, Engineering, and Mathematics (S-STEM), the Culturally Adaptive Pathway to Success (CAPS) program aims to build an inclusive pathway to accelerate the graduation for academically talented, low-income students in Engineering and Computer Science majors at [University Name], which traditionally serves the underrepresented and educationally disadvantaged minority students in the [City Name area]. CAPS focuses on progressively developing social and career competence in our students via three integrated interventions: (1) Mentor+, a relationally informed advising strategy that encourages students to see their academic work in relation to their families and communities; (2) peer cohorts, providing social support structure for students and enhancing their sense of belonging in engineering and computer science classrooms and beyond; and (3) professional development from faculty who have been trained in difference-education theory, so that they can support students with varying levels of understanding of the antecedents of college success. To ensure success of these interventions, the CAPS program places great emphasis on developing culturally responsive advisement methods and training faculty mentors to facilitate creating a culture of culturally adaptive advising. This paper presents the CAPS progress in the past two project years. In particular, we will share several changes that we have made after the first project year to improve several key components of the program - recruitment, cohort building, and mentor training. The program strengthened the recruitment by actively involving scholars and faculties in reaching out to students and successfully recruited more scholars for the second cohort (16 scholars) than the first cohort (12 scholars). Also, the program has initiated new activities for peer-mentoring and cohort gathering within each major. As continuous development of the mentor training, the program has added a training session focusing on various aspects of intersectionality as it relates to individual’s social identities, and how mentors can use these knowledge to better interact with mentees. In addition to these changes, we will also report findings on how the program impacted on scholars’ academic growth and mentors’ understanding about the culturally adaptive advisement to answer the CAPS research questions (a) how these interventions affect the development of social belonging and engineering identity of CAPS scholars, and (b) the impact of Mentor+ on academic resilience and progress to degree. The program conducted qualitative data collection and analysis via focus group meetings and interviews as well as quantitative data collection and analysis using academic records and surveys. Our findings will help enhance the CAPS program and establish a sustainable Scholars Support Program at the university, which can be implemented with scholarships funded by other sources, and which can be transferred to similar culturally diverse institutions to increase success for students who have socio-economic challenges. 

The Earth's upper mantle is isotopically heterogeneous over large lengthscales, but the lower limit of these heterogeneities is not well quantified. Grain scale trace elemental variability has been observed in mantle peridotites, which suggests that isotopic heterogeneity may be preserved as well. Recent advances in isotope ratio mass spectrometry enable isotopic analysis of very small samples (e.g., nanograms or less of analyte) while maintaining the precision necessary for meaningful interpretation. Here we examine four peridotite xenoliths—hosted in lavas from Savai'i (Samoa hotspot) and Tahiti (Societies hotspot) islands—that exhibit grain scale trace element heterogeneity likely related to trapped fluid and/or melt inclusions. To evaluate whether this heterogeneity is also reflected in grain scale isotopic heterogeneity, we separated clinopyroxene, orthopyroxene, and (in the most geochemically enriched xenolith) olivine for single‐grain⁸⁷Sr/⁸⁶Sr and¹⁴³Nd/¹⁴⁴Nd analyses. We find, in some xenoliths, extreme intra‐xenolith isotopic heterogeneity. For example, in one xenolith, different mineral grains range in⁸⁷Sr/⁸⁶Sr from 0.70987 to 0.71321, with corresponding variability in¹⁴³Nd/¹⁴⁴Nd from 0.512331 to 0.512462. However, not all peridotite xenoliths which display trace elemental heterogeneity exhibit isotopic heterogeneity. Based on coupled isotopic and trace element data (i.e., a negatively‐sloping trend in⁸⁷Sr/⁸⁶Sr vs. Ti/Eu), we suggest that carbonatitic metasomatism is responsible for creating the intra‐xenolith isotopic heterogeneities which we observe. This carbonatitic component falls off the array defined in⁸⁷Sr/⁸⁶Sr‐¹⁴³Nd/¹⁴⁴Nd space by Samoa hotspot basalts, which suggests a second, distinct EM2 (enriched mantle II) component is present in the Samoa hotspot that is not readily recognized in erupted products, but is instead seen only in mantle peridotite xenoliths.

 

The financial disadvantage of many students in the College of Engineering, Computer Science, and Technology (ECST) at California State University, Los Angeles, is often in parallel with inadequate academic preparation through K-12 education and limited family guidance. Hence, many students, including those who are academically-talented, experience significant challenges in achieving their academic goals. In 2018, the College of ECST received an award from NSF SSTEM program to establish a Culturally Adaptive Pathway to Success (CAPS) program that aims to build an inclusive pathway to accelerate the graduation for academically talented, lowincome students in Engineering and Computer Science majors. CAPS focuses on progressively developing students’ social and career competence via three integrated interventions: (1) Mentor+, relationally informed advising that encourages students to see their academic work in relation to their families and communities; (2) peer cohorts, providing social support structure for students and enhancing their sense of belongings in engineering and computer science classrooms and beyond; and (3) professional development with difference-education, illuminating the hidden curricula that may disadvantage first-generation and low income students. This paper presents our progress and core program activities during the first year of the CAPS program, including the recruitment process and mentor training program. In Fall 18, group and individual mentoring sessions have taken place following the culturally responsive mentoring strategy. In addition to program activities, the paper will also share the data collected through focus groups and report the lessons learned during the first-year implementation phase.