Identification of Terrestrial Alkalic Rocks Using Thermal Emission Spectroscopy: Applications to Martian Remote Sensing

We present a detailed study examining the use of laboratory thermal emission spectra (5-25 μm at 2 cm-1 spectral sampling) for identification and classification of alkalic volcanic rocks. Modal mineralogies and derived bulk rock chemistries of a suite of terrestrial alkali basalts, trachyandesites, trachytes, and rhyolites were determined using linear spectral deconvolution. Model-derived mineral modes were compared to modes measured using an electron microprobe mapping technique to access the accuracy of linear deconvolution in determining mineral abundances. Standard deviations of 1σ of absolute differences between measured and modeled mineral abundances range from 0.68 to 15.02 vol %, with an average of 5.67 vol %. Bulk-rock chemistries were derived by combining modeled end-member compositions (wt %) in proportion to their abundances (recalculated to wt %). Derived oxide data compare well with measured oxide data, with 1σ standard deviations ranging from 0.12 to 2.48 wt %. Modeled mineralogies, derived mineral chemistries, and derived bulk chemistries were examined to assess their accuracy in classifying alkalic rocks. Derived bulk chemistry is the most effective classification tool, modal mineralogy is the least, and basalts and rhyolites are typically more accurately classified than trachyandesites and trachytes. However, no single classification scheme can accurately identify all rock samples, indicating that a combination of classification schemes is necessary to distinguish alkalic volcanic rocks using thermal emission spectra. To examine the accuracy of volcanic rock classification at lower spectral resolutions, thermal emission spectra were resampled to the resolution of the Thermal Emission Spectrometer (TES) instrument (10 cm -1), and a second series of linear deconvolutions was performed. Results from modeled mineralogies and derived bulk-rock chemistries at 10 cm -1 are comparable to results at 2 cm -1 spectral sampling, indicating that this amount of degradation of spectral sampling does not adversely affect modal mineralogies and chemistries derived from linear deconvolution. Data from 10 cm -1 spectral sampling were applied to derived mineral and bulk chemistry classification schemes with high degrees of success. Overall, results from this study suggest that linear deconvolution of thermal emissivity spectra can be successfully applied to the identification and classification of alkalic volcanic rocks on Mars

Determination of Mineral Abundances in Ordinary Chondrites Using Powder X-ray Diffraction: Applications to Parent Body Processes and Asteroid Spectroscopy

The ordinary chondrites, the most abundant group of meteorites, are divided into three chemical groups (H, L, and LL), which are distinguished based on variations in bulk composition and iron content. Although ordinary chondrites are relatively abundant, our understanding of their formation has been hampered by an inability to accurately measure the abundances of minerals that they contain. Here I use power x-ray diffraction (XRD) to quantify the modal abundances of 48 unbrecciated ordinary chondrite falls, which represent the complete petrologic range of equilibrated ordinary chondrites (types 4-6). Although the degree of metamorphism varies within each ordinary chondrite group, many details regarding the geochemical and thermal changes that take place during this process are not well understood. Using XRD-measured modal mineral abundances and chemical analyses, we evaluate the redox state and peak metamorphic temperatures in ordinary chondrite parent bodies in order to develop quantitative thermal evolution models of ordinary chondrite parent asteroids. Modal abundances and mineral compositions measured in this study indicate that progressive oxidation of the ordinary chondrites likely occurred during metamorphism. Results also suggest that plagioclase crystallizes early in the metamorphic sequence, indicating that peak temperatures derived using the two-pyroxene geothermometer are more accurate than those calculated using the plagioclase geothermometer. I also utilize ordinary chondrite modal abundances to develop new calibrations for deriving mineralogy from meteorite and asteroid spectra. Most previous studies examining the mineralogical characteristics of VISNIR asteroid spectra have focused on olivine and pyroxene proportions in single-pyroxene mixtures; therefore, current calibrations for deriving composition mineral abundances may be poorly suited for asteroids containing more than one pyroxene. It is important that calibrations are correct, because mineral abundances derived from visible/near-infrared (VISNIR) spectra are used to classify asteroids, identify meteorite parent bodies, and understand the structure of the asteroid belt. Mineral abundances derived using my calibrations correlate well with measured data for all ordinary chondrites groups, and also appear to be valid for other meteorites and asteroids with mineral abundances and chemistries similar to those of the ordinary chondrites

Mineralogy and Surface Composition of Asteroids

Methods to constrain the surface mineralogy of asteroids have seen considerable development during the last decade with advancement in laboratory spectral calibrations and validation of our interpretive methodologies by spacecraft rendezvous missions. This has enabled the accurate identification of several meteorite parent bodies in the main asteroid belt and helped constrain the mineral chemistries and abundances in ordinary chondrites and basaltic achondrites. With better quantification of spectral effects due to temperature, phase angle, and grain size, systematic discrepancies due to non-compositional factors can now be virtually eliminated for mafic silicate-bearing asteroids. Interpretation of spectrally featureless asteroids remains a challenge. This paper presents a review of all mineralogical interpretive tools currently in use and outlines procedures for their application.Comment: Chapter to appear in the Space Science Series Book: Asteroids IV, 51 pages, 7 figures, 2 table

Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta

The detection of olivine on Vesta is interesting because it may provide critical insights into planetary differentiation early in our Solar System's history. Ground-based and Hubble Space Telescope (HST) observations of asteroid (4) Vesta have suggested the presence of olivine on the surface. These observations were reinforced by the discovery of olivine-rich HED meteorites from Vesta in recent years. However, analysis of data from NASA's Dawn spacecraft has shown that this olivine-bearing unit is actually impact melt in the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed during the formation of the 19 km deep Rheasilvia basin on Vesta's South Pole, further complicated this picture. Ammannito et al., (2013a) reported the discovery of local scale olivine-rich units in the form of excavated material from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. Here we explore alternative sources for the olivine in the northern hemisphere of Vesta by reanalyzing the data from the VIR instrument using laboratory spectral measurements of meteorites. We suggest that these olivine exposures could be explained by the delivery of olivine-rich exogenic material. Based on our spectral band parameters analysis, the lack of correlation between the location of these olivine-rich terrains and possible mantle-excavating events, and supported by observations of HED meteorites, we propose that a probable source for olivine seen in the northern hemisphere are remnants of impactors made of olivine-rich meteorites. Best match suggests these units are HED material mixed with either ordinary chondrites, or with some olivine-dominated meteorites such as R-chondrites.Comment: 62 pages, 12 figures, 4 tables; Icarus, Available online 30 January 2015, ISSN 0019-1035, http://dx.doi.org/10.1016/j.icarus.2015.01.01

The impact of immediate breast reconstruction on the time to delivery of adjuvant therapy: the iBRA-2 study

Background: Immediate breast reconstruction (IBR) is routinely offered to improve quality-of-life for women requiring mastectomy, but there are concerns that more complex surgery may delay adjuvant oncological treatments and compromise long-term outcomes. High-quality evidence is lacking. The iBRA-2 study aimed to investigate the impact of IBR on time to adjuvant therapy. Methods: Consecutive women undergoing mastectomy ± IBR for breast cancer July–December, 2016 were included. Patient demographics, operative, oncological and complication data were collected. Time from last definitive cancer surgery to first adjuvant treatment for patients undergoing mastectomy ± IBR were compared and risk factors associated with delays explored. Results: A total of 2540 patients were recruited from 76 centres; 1008 (39.7%) underwent IBR (implant-only [n = 675, 26.6%]; pedicled flaps [n = 105,4.1%] and free-flaps [n = 228, 8.9%]). Complications requiring re-admission or re-operation were significantly more common in patients undergoing IBR than those receiving mastectomy. Adjuvant chemotherapy or radiotherapy was required by 1235 (48.6%) patients. No clinically significant differences were seen in time to adjuvant therapy between patient groups but major complications irrespective of surgery received were significantly associated with treatment delays. Conclusions: IBR does not result in clinically significant delays to adjuvant therapy, but post-operative complications are associated with treatment delays. Strategies to minimise complications, including careful patient selection, are required to improve outcomes for patients

Breast cancer management pathways during the COVID-19 pandemic: outcomes from the UK ‘Alert Level 4’ phase of the B-MaP-C study

Abstract: Background: The B-MaP-C study aimed to determine alterations to breast cancer (BC) management during the peak transmission period of the UK COVID-19 pandemic and the potential impact of these treatment decisions. Methods: This was a national cohort study of patients with early BC undergoing multidisciplinary team (MDT)-guided treatment recommendations during the pandemic, designated ‘standard’ or ‘COVID-altered’, in the preoperative, operative and post-operative setting. Findings: Of 3776 patients (from 64 UK units) in the study, 2246 (59%) had ‘COVID-altered’ management. ‘Bridging’ endocrine therapy was used (n = 951) where theatre capacity was reduced. There was increasing access to COVID-19 low-risk theatres during the study period (59%). In line with national guidance, immediate breast reconstruction was avoided (n = 299). Where adjuvant chemotherapy was omitted (n = 81), the median benefit was only 3% (IQR 2–9%) using ‘NHS Predict’. There was the rapid adoption of new evidence-based hypofractionated radiotherapy (n = 781, from 46 units). Only 14 patients (1%) tested positive for SARS-CoV-2 during their treatment journey. Conclusions: The majority of ‘COVID-altered’ management decisions were largely in line with pre-COVID evidence-based guidelines, implying that breast cancer survival outcomes are unlikely to be negatively impacted by the pandemic. However, in this study, the potential impact of delays to BC presentation or diagnosis remains unknown