Ultramafic xenoliths from the Bearpaw Mountains, Montana, USA: evidence for multiple metasomatic events in the lithospheric mantle beneath the Wyoming craton

Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountains volcanic field (Montana, USA), derived from the lower lithosphere of the Wyoming craton, can be divided based on textural criteria into tectonite and cumulate groups. The tectonites consist of strongly depleted spinel lherzolites, harzburgites and dunites. Although their mineralogical compositions are generally similar to those of spinel peridotites in off-craton settings, some contain pyroxenes and spinels that have unusually low Al2O3 contents more akin to those found in cratonic spinel peridotites. Furthermore, the tectonite peridotites have whole-rock major element compositions that tend to be significantly more depleted than non-cratonic mantle spinel peridotites (high MgO, low CaO, Al2O3 and TiO2) and resemble those of cratonic mantle. These compositions could have been generated by up to 30% partial melting of an undepleted mantle source. Petrographic evidence suggests that the mantle beneath the Wyoming craton was re-enriched in three ways: (1) by silicate melts that formed mica websterite and clinopyroxenite veins; (2) by growth of phlogopite from K-rich hydrous fluids; (3) by interaction with aqueous fluids to form orthopyroxene porphyroblasts and orthopyroxenite veins. In contrast to their depleted major element compositions, the tectonite peridotites are mostly light rare earth element (LREE)-enriched and show enrichment in fluid-mobile elements such as Cs, Rb, U and Pb on mantle-normalized diagrams. Lack of enrichment in high field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf) suggests that the tectonite peridotites have been metasomatized by a subduction-related fluid. Clinopyroxenes from the tectonite peridotites have distinct U-shaped REE patterns with strong LREE enrichment. They have 143Nd/144Nd values that range from 0·5121 (close to the host minette values) to 0·5107, similar to those of xenoliths from the nearby Highwood Mountains. Foliated mica websterites also have low 143Nd/144Nd values (0·5113) and extremely high 87Sr/86Sr ratios in their constituent phlogopite, indicating an ancient (probably mid-Proterozoic) enrichment. This enriched mantle lithosphere later contributed to the formation of the high-K Eocene host magmas. The cumulate group ranges from clinopyroxene-rich mica peridotites (including abundant mica wehrlites) to mica clinopyroxenites. Most contain >30% phlogopite. Their mineral compositions are similar to those of phenocrysts in the host minettes. Their whole-rock compositions are generally poorer in MgO but richer in incompatible trace elements than those of the tectonite peridotites. Whole-rock trace element patterns are enriched in large ion lithophile elements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb, Ta Zr and Hf) as in the host minettes, and their Sr–Nd isotopic compositions are also identical to those of the minettes. Their clinopyroxenes are LREE-enriched and formed in equilibrium with a LREE-enriched melt closely resembling the minettes. The cumulates therefore represent a much younger magmatic event, related to crystallization at mantle depths of minette magmas in Eocene times, that caused further metasomatic enrichment of the lithosphere

Carnivore conservation planning on Borneo: identifying key carnivore landscapes, research priorities and conservation interventions

Borneo harbours more endemic carnivores than does any other island in the world except Madagascar, and almost half of the Bornean carnivore species have been classified by The IUCN Red List of Threatened Species as globally threatened. Here, a systematic conservation planning framework highlighted key carnivore landscapes, conservation research and intervention priorities, and gaps in current knowledge of Bornean carnivore ecology. All single-species predictive habitat suitability index (HSI) models presented in this issue (20 species, comprising all carnivores on Borneo except otters [Lutrinae] and sun bear Helarctos malayanus) were standardised by converting HSI values into binary maps, and combined to derive species richness maps to discuss and delineate areas of conservation priority. The highest predicted carnivore species richness (defined here as the sum of the binary threshold maps), corresponds to interior lowland, upland and lower montane forest, whereas areas with lowest predicted species richness correspond to coastal lowlands already largely converted to oil palm plantations. The 12 proposed areas of conservation importance for carnivores focus on large landscapes and connectivity between subunits, many centred around the tri-national Heart of Borneo initiative, with additional areas for wetland/lowland species. A large proportion of these proposed conservation landscapes are being exploited for commercial purposes (e.g., logging concessions) and would, therefore, improve in conservation value if their management became more sustainable. The most important research priorities for Bornean carnivores are species resilience to altered and fragmented landscapes; under-surveyed regions; and the effects and relative intensity of hunting across the island. The most pressing conservation interventions include conservation research on the most threatened Bornean carnivores: the Bornean ferret badger Melogale everetti and Hose’s civet Diplogale hosei (highland endemics), and the flatheaded cat Prionailurus planiceps and otter civet Cynogale bennettii (wetland specialists). Targeted conservation research and integration of research findings into decision-making, maintaining and restoring connectivity, raising awareness and improving enforcement and governance are also important conservation interventions. Although more resources are needed for conservation and research, the joint effort of scientists, conservationists and government authorities in the identification of key carnivore landscapes, research priorities and conservation issues which this study presents raises hope that more targeted conservation efforts for Bornean carnivores will follow in the future