Virginia L. Peterson

Coexisting clinopyroxene/spinel and amphibole/spinel symplectites in metatroctolites from the Buck Creek ultramafic body, North Carolina Blue Ridge

Abstract Buck Creek metatroctolites preserve evidence of three stages in the geologic history of the region: a relict igneous stage; a high-pressure, granulite-facies metamorphic stage; and a hydrous alteration stage. During high-pressure granulite-facies metamorphism, adjacent olivine and plagioclase reacted to produce complex coronitic textures. Relict olivine is surrounded by radial, columnar orthopyroxene, and plagioclase is rimmed by fine-grained symplectite composed of separate grains of clinopyroxene/ spinel, tschermakitic amphibole/spinel symplectite and minor clinopyroxene/sapphirine symplectite. Examination of textural relationships in back-scattered electron images and X-ray element maps of the symplectites demonstrates that amphibole/spinel and clinopyroxene/spinel symplectites grew simultaneously at high temperature to replace plagioclase in these rocks. Clinopyroxene/sapphirine symplectite grew in the latest stages of plagioclase replacement in some samples. A successful model for the main corona-forming reaction in sample BC7, 1.00 Pl + 1.72 Ol + 0.17 H2O = 0.59 Di + 0.17 Amp + 0.68 Spl + 0.79 Opx, results only if amphibole is included. The model predicts relative volumes of product clinopyroxene, amphibole and spinel that are generally consistent with the proportions in imaged symplectites. Proportions of clinopyroxene- and amphibole-hosted symplectite appear to have been governed by local mass-balance of Na and Al in plagioclase and/or availability of H2O. The most successful model for formation of the inner clinopyroxene/sapphirine corona, 1.00 Pl + 1.47 Ol + 0.17 H2O = 0.59 Di + 0.17 Amp + 0.30 Spr (10 ox.) + 0.57 Opx, also includes amphibole, which is present in association with clinopyroxene/sapphirine symplectite. Sufficient H2O for formation of symplectic amphibole must have been present in the intergranular fluid of relict igneous troctolites or have infiltrated during metamorphism at high P-T conditions.

Petrogenesis and Structure of the Buck Creek Mafic-Ultramafic Suite, Southern Appalachians: Constraints on Ophiolite Evolution and Emplacement in Collisional Orogens

Integration of detailed field, petrological, structural, and geochemical observations of the Buck Creek mafic-ultramafic suite, which is among the larger southern Appalachian ultramafic exposures, points to an igneous origin as a mid-ocean-ridge cumulate massif, with subsequent emplacement in a deep subduction-zone setting. These results help to clarify the unresolved role of “alpine-type” ultramafic bodies in the southern Appalachians, a problem complicated by their generally small and fragmented nature and by significant tectonic overprinting. As an ophiolite fragment, the Buck Creek rocks are unusual in their preservation of relatively high-pressure, anhydrous conditions, and thus they provide constraints on mechanisms of ophiolite emplacement. Field support for a cumulate origin for the Buck Creek suite includes centimeter- to meter-scale interlayering of dunite, troctolite, anorthosite, and spinel-rich layers, and local gradation between Buck Creek troctolitic rocks and surrounding amphibolites. Relict anorthitic plagioclase, forsteritic olivine, and augitic clinopyroxene define a “cumulate triangle” on an MgO versus Al 2 O 3 diagram: meta-troctolite and meta-dunite compositions define a linear array between olivine and plagioclase compositions, and many amphibolites fall within this triangle, reflecting gabbroic protoliths. The relatively abundant troctolite cumulates, scarce pyroxene in the ultramafic rocks, and the high Al 2 O 3 /TiO 2 and low Cr numbers in spinel best match LOT- or L-type (lherzolite) ophiolites, consistent with crystallization in a slow-spreading mid-ocean-ridge setting. Sapphirine-bearing, spinel symplectites in the metatroctolites suggest that Buck Creek rocks remained anhydrous to ~800 °C and ~0.9–1.1 GPa, representing conditions atypical of ophiolite emplacement. Comparisons to the Zermatt-Saas ophiolite and Bergen eclogite suggest rapid subduction of Buck Creek rocks to depths of ~30 km, where partial hydration, perhaps facilitated by pro-grade dehydration reactions in surrounding rocks, caused strain softening that permitted ductile disaggregation and aided in their emplacement into the overlying accretionary complex. Alternatively, emplacement might have resulted from a switch in subduction polarity, with hydration following emplacement. Uplift, shortening, and hydration within the accretionary sequences are responsible for the dominant structural features.

Enhancing participation of two-year college faculty in The Geological Society of America

A strategic goal of The Geological Society of America (GSA) is to increase two-year college (2YC) faculty membership. In 2009, the GSA Committee on Education conducted a survey of 2YC faculty and explored strategies by which GSA might better serve them. We suggest that GSA provide increased professional and networking opportunities for 2YC faculty and encourage GSA members teaching at four-year colleges and universities to engage this cohort through lectures, colloquia, seminars, field trips, and research–teaching collaborations. INTRODUCTION Two-year colleges (2YCs) and their faculty are critical to the growth and development of the geoscience workforce (AGI, 2009). Increasing the number of 2YC faculty who are GSA members, enhancing resources for these members and their students, and increasing their participation in both annual and Section meetings are GSA strategic objectives (GSA, 2008). The increase in GSA membership among 2YC faculty (currently 374 members [1.6% of the total membership], an increase of ~100 members since 2006) is modest relative to the strategic goal of 1,000 members by 2011. The GSA Committee on Education (“Committee”) has investigated strategies by which GSA can better serve and attract 2YC faculty members. In late 2008, the Committee conducted a survey of 2YC faculty to better understand the needs of this community. The Committee also organized welcome receptions for 2YC geoscience faculty at GSA’s 2009 and 2010 annual meetings, both for networking and for information gathering. Here, we present Committee findings and suggest strategies for better inclusion of 2YC geoscience faculty. RATIONALE In the United States, 2YCs enroll 44% of all undergraduate students (AACC, 2011). Approximately 65% of graduating high school seniors decide to attend college after graduation, and of those students, 30% matriculate to a 2YC (Chen, 2009). 2YCs contribute significantly to the development of the STEM skills (NSB, 2010) needed for twenty-first–century learning and for bridging K–12 and higher education institutions, informal science education organizations, business, and industry. Thus, 2YC faculty play an important role in broadening geoscience literacy and attracting students and future teachers to the geoscience workforce (Williams, 2010) but appear to be both underrepresented and underserved within GSA. REPORT ON THE 2YC FACULTY SURVEY The Committee designed an online Zoomerang (www .zoomerang.com) survey to identify aspects of GSA membership most valued by 2YC faculty and to gain perspectives on how the Society might better serve this population. The survey, made available for two months (December 2008–January 2009), included 26 multiple-choice/fill-in questions plus openresponse options for additional comments or clarifications. The absence of a comprehensive national list of geoscience faculty at 2YCs was identified early on as an impediment for communication and networking amongst this cohort, and this limited our ability to involve survey participants beyond the GSA membership. Current GSA members who self-identified as 2YC faculty were invited to participate in the survey; non-GSA members learned of the survey through networking. Methods The authors compiled and coded all survey data. Survey questions and responses are available for review on the GSA Education and Outreach website (www.geosociety.org/educate/ documents/1106-2YCsurvey.pdf). Multiple-choice responses were automatically tallied, with the sums of each response type reported as a percentage of total responses for a given item. Open responses (textual), ranging from single words to short paragraphs, were reported in the form of lists of responses by item. Each list was coded separately to identify and distinguish the most common themes expressed by respondents. Open responses for each item were grouped by emergent themes and reported as percentages of the total number of open responses for each item. About half of the items were deemed to have too few open responses for meaningful coding. Results The survey’s 137 respondents had been teaching on average for 11 ± 8 years. More than 90% were GSA members, and a significant number (60%) had attended GSA meetings at least GSA Today, v. 21, no. 12, doi: 10.1130/G130GW.1 E-mails: Peterson: petersvi@gvsu.edu; Garver: garverj@union.edu; Semken: semken@asu.edu; Williams: wwilliams@nwacc.edu. Enhancing participation of two-year college faculty in The Geological Society of America GROUNDWORK T H E G EO LO GI CAL SCIETY OF AM ERIC A Furthering the Inf luence of Earth Science