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Geochronology, geochemistry and Nd, Sr and Pb isotopes of syn-orogenic granodiorites and granites (Damara orogen, Namibia) – arc-related plutonism or melting of mafic crustal sources?

Highlights • Geochemical data from high-T granodiorites and granites imply lower crustal amphibolite melting. • New U-Pb zircon ages imply syn-orogenic intrusion • New Sr-Nd-Pb isotope data imply ancient crustal sources and constrain AFC processes Abstract: The Gawib pluton (Damara Belt, Namibia) consists of two main intrusive rock types; magnesian, calc-alkaline, mostly metaluminous hornblende- and titanite-bearing granodiorites and magnesian to ferroan, metaluminous to slightly peraluminous calc-alkaline granites. Uranium-Pb zircon data obtained on the granodiorites gave concordant ages of 548.5 ± 5.6 Ma indicating that the pluton belongs to the early syn-orogenic magmatism in the Damara orogen. Major and trace element variations indicate that fractional crystallization was the major rock-forming mechanism for the granodiorites. In the absence of high-precision geochronological data, the granites may represent more advanced fractionation products of the granodiorites although distinct Ba-Sr-Rb relationships preclude a direct derivation of the granites from the exposed granodiorites. If the granites originated by extensive fractional crystallization from similar granodiorites, they can only be derived from high-Ba, high-Sr, low-Rb granodiorites. Crustal contamination was also important in the petrogenesis of both rock types (granodiorites: ε Nd(init.): -7 to -13; 87Sr/86Sr(init.): 0.708-0.713; granites: ε Nd(init): -14 to -18; 87Sr/86Sr(init.): 0.712-0.726). In contrast to the granodiorites, the granites show more radiogenic 87Sr/86Sr ratios and less radiogenic ε Nd values indicating different contaminants for both rock types. ε Nd vs. MgO relationships imply some genetic link to isotopically unevolved quartz diorites similar to those observed at the Palmental complex. This pluton, however, is located c. 80 km NE from the Gawib pluton and probably cannot be viewed as the direct source of the Gawib granodiorites. If such a relationship is allowed, the granodiorites must be viewed as hybrid rocks containing a juvenile component because they were derived from unevolved quartz diorites by fractional crystallization. In addition, AFC processe have also played a role implying that the granodiorites contain also a reprocessed crustal component. Alternatively, comparison with experimentally derived melts imply that the granodiorites are generated by dehydration melting of a mafic, amphibole-bearing lower crustal source. Chemical parameters of the granodiorites compared to experimental results indicate high temperatures of c. 1040 °C. Zirconium saturation temperatures obtained on the most primitive samples gave c. 830 °C whereas apatite saturation temperatures obtained on the same samples give temperatures of c. 960-980 °C; the latter seems to be a more reliable temperature estimate. Interpretation of geochemical and isotope data from the complex suggest that the early synorogenic Pan-African igneous activity in this part of the Damara Belt was a high-temperature intra-crustal event. In contrast to igneous processes along active continental margins that produce also intermediate plutons with calc-alkaline affinities, this igneous event was not a major crust-forming episode and the granodiorites represent mostly reprocessed crustal material

Petrogenesis of a late-stage calc-alkaline granite in a giant S-type batholith: geochronology and Sr–Nd–Pb isotopes from the Nomatsaus granite (Donkerhoek batholith), Namibia

The late-tectonic 511.4 ± 0.6 Ma-old Nomatsaus intrusion (Donkerhoek batholith, Damara orogen, Namibia) consists of moderately peraluminous, magnesian, calc-alkalic to calcic granites similar to I-type granites worldwide. Major and trace-element variations and LREE and HREE concentrations in evolved rocks imply that the fractionated mineral assemblage includes biotite, Fe–Ti oxides, zircon, plagioclase and monazite. Increasing K2O abundance with increasing SiO2 suggests accumulation of K-feldspar; compatible with a small positive Eu anomaly in the most evolved rocks. In comparison with experimental data, the Nomatsaus granite was likely generated from meta-igneous sources of possibly dacitic composition that melted under water-undersaturated conditions (X H2O: 0.25–0.50) and at temperatures between 800 and 850 °C, compatible with the zircon and monazite saturation temperatures of 812 and 852 °C, respectively. The Nomatsaus granite has moderately radiogenic initial 87Sr/86Sr ratios (0.7067–0.7082), relatively radiogenic initial εNd values (− 2.9 to − 4.8) and moderately evolved Pb isotope ratios. Although initial Sr and Nd isotopic compositions of the granite do not vary with SiO2 or MgO contents, fSm/Nd and initial εNd values are negatively correlated indicating limited assimilation of crustal components during monazite-dominated fractional crystallization. The preferred petrogenetic model for the generation of the Nomatsaus granite involves a continent–continent collisional setting with stacking of crustal slices that in combination with high radioactive heat production rates heated the thickened crust, leading to the medium-P/high-T environment characteristic of the southern Central Zone of the Damara orogen. Such a setting promoted partial melting of metasedimentary sources during the initial stages of crustal heating, followed by the partial melting of meta-igneous rocks at mid-crustal levels at higher P–T conditions and relatively late in the orogenic evolution

I Didn\u27t Know How All This Works : A Case Study Examining The Transition Experiences of Student-Athletes from High School to a Mid-Major DI Program

The transition period from high school to college includes a myriad of issues specific to student-athletes (Bernhard & Bell, 2015; Bjornsen & Dinkel, 2017; Comeaux, 2015). The present study sought to illuminate the specific transition issues faced by mid-major, DI student-athletes by providing them the platform to describe them in their own words, and provide their own recommendations for improvement. Utilizing a semi-structured interview guide which addressed transition issues, the qualitative study included 23 student-athletes in focus group settings. Analysis of interview data led to the emergence of two themes, with accompanying subthemes: 1) Encounters with academic support, with subthemes of transitioning to campus and perceived responsibilities of athletic academic advisors; and 2) Skewed perceptions and expectations of student-athlete life, with subthemes of expectations regarding the coach-athlete relationship, lifestyle modifications, and high stress practice environments. The findings suggest a notable trend – student-athletes lack the support they need to successfully deal with the transition. The transition process itself also appears to involve three specific periods: 1) Prior to arrival on campus; 2) Initial arrival on campus; and 3) Following the initial transition to campus. The findings will help to better design standards for helping student-athletes navigate the transition process

Petrogenesis of synorogenic high-temperature leucogranites (Damara orogen, Namibia): Constraints from U–Pb monazite ages and Nd, Sr and Pb isotopes

Highlights: • Geochemical data from high-T leucogranites imply pure crustal melting. • New U–Pb monazite ages constrain intrusion time close to peak metamorphism. • Updated Sr–Nd–Pb isotope data imply metasedimentary sources. Two suites of leucogranites were emplaced at 508 ± 5.9 Ma in the Okombahe District of the Damara belt (Namibia) synchronous with the peak of regional high-temperature metamorphism. The Sr (87Sr/86Srinit: 0.707 to 0.711), Nd (εNdinit: − 4.5 to − 6.6), and Pb isotopic (206Pb/204Pb: 18.51–19.13; 207Pb/204Pb: 15.63–15.69; 208Pb/204Pb: 38.08–38.66) compositions indicate that these peraluminous S-type granites were derived from mid- to lower-crustal rocks, which are slightly different to the metapelitic rocks into which they intruded. Since the leucogranites are unfractionated and show no evidence for assimilation or contamination, they constrain the temperature and pressure conditions of their formation. Calculated Zr and LREE saturation temperatures of ca. 850 °C indicate high-temperature crustal melts. High Rb/Sr and low Sr/Ba ratios are consistent with biotite dehydration melting of pelitic source rocks. Qz–Ab–Or systematics reveal that melting and segregation for the least fractionated samples occurred at ca. 7 kbar corresponding to a mid-crustal level of ca. 26 km. However, there is no evidence for a mantle component that could have served as a local heat source for crustal melting. Therefore, the hot felsic magmas that formed close to the time of peak metamorphism are the result of long-lasting high temperature regional metamorphic conditions and intra-crustal collision

A Textured Silicon Calorimetric Light Detector

We apply the standard photovoltaic technique of texturing to reduce the reflectivity of silicon cryogenic calorimetric light detectors. In the case of photons with random incidence angles, absorption is compatible with the increase in surface area. For the geometrically thin detectors studied, energy resolution from athermal phonons, dominated by position dependence, is proportional to the surface-to-volume ratio. With the CaWO4 scintillating crystal used as light source, the time constants of the calorimeter should be adapted to the relatively slow light-emission times.Comment: Submitted to Journal of Applied Physic

The ν\nu-cleus experiment: A gram-scale fiducial-volume cryogenic detector for the first detection of coherent neutrino-nucleus scattering

We discuss a small-scale experiment, called $\nu$-cleus, for the first detection of coherent neutrino-nucleus scattering by probing nuclear-recoil energies down to the 10 eV-regime. The detector consists of low-threshold CaWO$_4$ and Al$_2$O$_3$ calorimeter arrays with a total mass of about 10 g and several cryogenic veto detectors operated at millikelvin temperatures. Realizing a fiducial volume and a multi-element target, the detector enables active discrimination of $\gamma$, neutron and surface backgrounds. A first prototype Al$_2$O$_3$ device, operated above ground in a setup without shielding, has achieved an energy threshold of ${\sim20}$ eV and further improvements are in reach. A sensitivity study for the detection of coherent neutrino scattering at nuclear power plants shows a unique discovery potential (5$\sigma$) within a measuring time of ${\lesssim2}$ weeks. Furthermore, a site at a thermal research reactor and the use of a radioactive neutrino source are investigated. With this technology, real-time monitoring of nuclear power plants is feasible.Comment: 14 pages, 19 figure