Campaign-style U-Pb titanite petrochronology: along-strike variations in timing of metamorphism in the Himalayan Metamorphic Core

Present-day along-strike heterogeneities within the Himalayan orogen are seen at many scales, from variations within the deep architecture of the lithospheric mantle, to differences in geomorphologic surface processes. Here, we present an internally consistent petrochronologic dataset from the Himalayan metamorphic core (HMC), in order to document and investigate the causes of along-strike variations in its Oligocene–Miocene tectonic history. Laser ablation split-stream analysis was used to date and characterise the geochemistry of titanite from 47 calc-silicate rocks across >2000 km along the Himalaya. This combined U-Pb-REE-Zr single mineral dataset circumvents uncertainties associated with interpretations based on data compilations from different studies, mineral systems and laboratories, and allows for direct along-strike comparisons in the timing of metamorphic processes. Titanite dates range from ∼30 Ma to 12 Ma, recording (re-)crystallization between 625 °C and 815 °C. Titanite T-t data overlap with previously published P-T-t paths from interleaved peltic rocks, demonstrating the usefulness of titanite petrochronology for recording the metamorphic history in lithologies not traditionally used for thermobarometry. Overall, the data indicate a broad eastward-younging trend along the orogen. Disparities in the duration and timing of metamorphism within the HMC are best explained by along-strike variations in the position of ramps on the basal detachment controlling a two-stage process of preferential ductile accretion at depth followed by the formation of later upper-crust brittle duplexes. These processes, coupled with variable erosion, resulted in the asymmetric exhumation of a younger, thicker crystalline core in the eastern Himalaya. Keywords: Himalaya, Petrochronology, Titanite, Metamorphic petrolog

Contrasting accessory mineral behavior in minimum-temperature melts: Empirical constraints from the Himalayan metamorphic core

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.lithos.2018.05.003 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Medium-grained leucogranite in the Tama Kosi region of the Nepalese Himalayan Metamorphic Core yields a relatively narrow range of monazite 208Pb/232Th dates with a dominant population at ~21.0 Ma inferred to represent crystallization of an early plutonic phase. In contrast, the pegmatitic portion of the same intrusive complex, that cross-cuts the medium-grained leucogranite, contains zircon, monazite and xenotime that each display near-identical age spectra, recording semi-continuous (re-)crystallization from 27.5 Ma to 21.0 Ma, followed by a ~2 m.y. hiatus then further (re-)crystallization between 19.4 and 18.6 Ma. The “gap” in pegmatite dates corresponds well to the crystallization age of the older leucogranite, whereas the end of accessory phase growth in the pegmatite coincides with the onset of regional-scale cooling. Detailed textural, trace element and thermochronologic data indicate that the range of zircon, monazite and xenotime dates recorded in the pegmatite reflect inherited components that underwent semi-continuous (re-)crystallization during metamorphism and/or anatexis in the source region(s), whereas dates younger than the hiatus indicate accessory phase recrystallization, related to both fluid influx and a concomitant increase in temperature. In contrast, the lack of an inherited component(s) in the medium-grained leucogranite phase is inferred to be a result of complete dissolution during partial melting. A model is proposed in which influx of heat and H2O-rich fluids associated with early leucogranite emplacement temporarily delayed zircon and monazite and xenotime crystallization, respectively. These data highlight the importance of measuring spatially resolved dates, trace elements and textural patterns from multiple accessory minerals combined with model constraints to better understand the often-complex crystallization history of anatectic melts in collisional orogens.NSF grant (EAR-1119380)NSERC Discovery and Canadian Foundation for Innovation (RGPIN-2016-06736

Advances in Isotope Ratio Determination by LA–ICP–MS

LA–ICP–MS has proven to be an extremely important analytical tool within the Earth, environmental, and archaeological sciences. New developments in both instrumentation and methodology now provide the ability to extract age and isotopic tracer information in situ at a variety of scales (from nm to cm), in 2- and 3-dimensions, quickly and cost-effectively, providing considerable analytical flexibility compared to other micro-analytical techniques. Here, we review the current state of the art in laser ablation isotope ratio determination and provide some insights into future developments

Development of an incipient Paleogene topography between the present-day Eastern Andean Plateau (Puna) and the Eastern Cordillera, southern Central Andes, NW Argentina

The structural and topographic evolution of orogenic plateaus is an important research topic because of its impact on atmospheric circulation patterns, the amount and distribution of rainfall, and resulting changes in surface processes. The Puna region in the north-western Argentina (between 13°S and 27°S) is part of the Andean Plateau, which is the world's second largest orogenic plateau. In order to investigate the deformational events responsible for the initial growth of this part of the Andean plateau, we carried out structural and stratigraphic investigations within the present-day transition zone between the northern Puna and the adjacent Eastern Cordillera to the east. This transition zone is characterized by ubiquitous exposures of continental middle Eocene redbeds of the Casa Grande Formation. Our structural mapping, together with a sedimentological analysis of these units and their relationships with the adjacent mountain ranges, has revealed growth structures and unconformities that are indicative of syntectonic deposition. These findings support the notion that tectonic shortening in this part of the Central Andes was already active during the middle Paleogene, and that early Cenozoic deformation in the region that now constitutes the Puna occurred in a spatially irregular manner. The patterns of Paleogene deformation and uplift along the eastern margin of the present-day plateau correspond to an approximately north-south oriented swath of reactivated basement heterogeneities (i.e. zones of mechanical weakness) stemming from regional Paleozoic mountain building that may have led to local concentration of deformation belts.Fil: Montero López, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Hongn, Fernando Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: López Steinmetz, Romina Lucrecia. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; ArgentinaFil: Aramayo, Alejandro José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Pingel, Heiko. Universitat Potsdam; AlemaniaFil: Strecker, Manfred R.. Universitat Potsdam; AlemaniaFil: Cottle, John M.. University of California; Estados UnidosFil: Bianchi, Carlos Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentin

Re-evaluating monazite as a record of metamorphic reactions

ABSTRACT: This study presents a re-examination of historical specimens (DG136 and DG167) from the Monashee complex in the southeastern Canadian Cordillera that are critical to the current understanding of rare earth element (REE) distribution between garnet and monazite (and other accessory minerals) during metamorphism. Nine-hundred and fifty-one new monazite petrochronology spot analyses on 29 different grains across two specimens outline detailed (re)crystallization histories. Trace element data collected from the same ablated volume, interpreted in the context of new phase equilibria modelling that includes monazite, xenotime and apatite, link ages to specific portions of the pressure-temperature (P-T) paths followed by the specimens. These linkages are further informed by garnet Lu-Hf geochronology and xenotime petrochronology. The clockwise P-T paths indicate prograde metamorphism was ongoing by ca. 80 Ma in both specimens. The structurally deeper specimen, DG136, records peak P-T conditions of similar to 755-770 degrees C and 8.8-10.4 kbar, interpreted to coincide with (re-)crystallization of low Y monazite at similar to 75-70 Ma. Near-rim garnet isopleths from DG167 cross in the observed peak assemblage field at similar to 680 degrees C and 9.3 kbar. These conditions are interpreted to correspond with low Y monazite (re-)crystallisation at similar to 65 Ma. Both specimens record decompression along their retrograde path coincident with high Y 70-55 Ma and 65-55 Ma monazite populations in DG136 and DG167, respectively. These findings broadly agree with those initially reported similar to 20 years ago and confirm early interpretations using trace elements in monazite as generally reliable markers of metamorphic reactions. Modern phase equilibria modelling and in situ petrochronological analysis, however, provide additional insight into monazite behaviour during anatexis and the effects of potential trace element buffering by REE-bearing phases such as apatite. (C) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V

Identification of genes important for cutaneous function revealed by a large scale reverse genetic screen in the mouse.

The skin is a highly regenerative organ which plays critical roles in protecting the body and sensing its environment. Consequently, morbidity and mortality associated with skin defects represent a significant health issue. To identify genes important in skin development and homeostasis, we have applied a high throughput, multi-parameter phenotype screen to the conditional targeted mutant mice generated by the Wellcome Trust Sanger Institute's Mouse Genetics Project (Sanger-MGP). A total of 562 different mouse lines were subjected to a variety of tests assessing cutaneous expression, macroscopic clinical disease, histological change, hair follicle cycling, and aberrant marker expression. Cutaneous lesions were associated with mutations in 23 different genes. Many of these were not previously associated with skin disease in the organ (Mysm1, Vangl1, Trpc4ap, Nom1, Sparc, Farp2, and Prkab1), while others were ascribed new cutaneous functions on the basis of the screening approach (Krt76, Lrig1, Myo5a, Nsun2, and Nf1). The integration of these skin specific screening protocols into the Sanger-MGP primary phenotyping pipelines marks the largest reported reverse genetic screen undertaken in any organ and defines approaches to maximise the productivity of future projects of this nature, while flagging genes for further characterisation

Key features of palliative care service delivery to Indigenous peoples in Australia, New Zealand, Canada and the United States: A comprehensive review

Background: Indigenous peoples in developed countries have reduced life expectancies, particularly from chronic diseases. The lack of access to and take up of palliative care services of Indigenous peoples is an ongoing concern. Objectives: To examine and learn from published studies on provision of culturally safe palliative care service delivery to Indigenous people in Australia, New Zealand (NZ), Canada and the United States of America (USA); and to compare Indigenous peoples’ preferences, needs, opportunities and barriers to palliative care. Methods: A comprehensive search of multiple databases was undertaken. Articles were included if they were published in English from 2000 onwards and related to palliative care service delivery for Indigenous populations; papers could use quantitative or qualitative approaches. Common themes were identified using thematic synthesis. Studies were evaluated using Daly’s hierarchy of evidence-for-practice in qualitative research. Results: Of 522 articles screened, 39 were eligible for inclusion. Despite diversity in Indigenous peoples’ experiences across countries, some commonalities were noted in the preferences for palliative care of Indigenous people: to die close to or at home; involvement of family; and the integration of cultural practices. Barriers identified included inaccessibility, affordability, lack of awareness of services, perceptions of palliative care, and inappropriate services. Identified models attempted to address these gaps by adopting the following strategies: community engagement and ownership; flexibility in approach; continuing education and training; a whole-of-service approach; and local partnerships among multiple agencies. Better engagement with Indigenous clients, an increase in number of palliative care patients, improved outcomes, and understanding about palliative care by patients and their families were identified as positive achievements. Conclusions: The results provide a comprehensive overview of identified effective practices with regards to palliative care delivered to Indigenous populations to guide future program developments in this field. Further research is required to explore the palliative care needs and experiences of Indigenous people living in urban areas