Thermochronological evolution of calcite formation at the potential Yucca Mountain repository site, Nevada: Part 2 fluid inclusion analyses and UPb dating

The presence of two-phase fluid inclusions in thin secondary mineral crusts at the potential Yucca Mountain nuclear waste repository has raised questions regarding the origin, timing, and temperature of past fluid flow through the repository horizon. The geologically recent passage of fluids with high temperatures would call into question the suitability of the site for the storage of high level nuclear waste. This study determined the thermal history of fluid flow through the site using fluid inclusion analyses and constrained the timing of thermal fluids by dating silica minerals spatially associated with the fluid inclusions using U-Pb techniques. Results provide a detailed time-temperature history of fluid migration through primary and secondary pore spaces during the past 8 to 9 million years. One hundred and fifty-five samples were collected in the unsaturated zone from the C-shaped Exploratory Studies Facility (ESF), the ECRB cross drift which crosses the potential repository horizon, and exploratory alcoves. Detailed petrographic and paragenetic studies indicated that the oldest secondary minerals consisted of heterogeneously distributed calcite with lesser chalcedony, quartz, opal, and fluorite. The oldest secondary minerals were overgrown by intermediate bladed calcite. The youngest secondary minerals include chemically distinct Mgenriched, growth-zoned sparry calcite (MGSC) and intergrown U-enriched opal. Fluid inclusion petrography indicated that 50 % of the samples (n = 78) contained fluid inclusion assemblages with two-phase fluid inclusions, and that assemblages of liquid-only fluid inclusions represent \u3e 96% of all fluid inclusions within the secondary minerals. Assemblages of two-phase inclusions also contain liquid-only inclusions that did not nucleate a vapor-bubble owing to formation at relatively low temperatures. Virtually all two-phase fluid inclusions occur in paragenetically old calcite; rare two-phase inclusion assemblages were observed in old fluorite (n = 3) and quartz (n = 2). Rare two-phase fluid inclusions were observed in early-intermediate calcite; sparse, irregularly shaped liquid-only inclusions form the only fluid inclusion assemblages observed in late-intermediate minerals and young MGSC. Homogenization temperatures for calcite across the site are generally 45 - 60 °C, but higher temperatures reaching 83 °C were recorded in the north portal and ramp of the ESF and cooler temperatures of ~ 35 - 45 °C were recorded in the intensely fracture zone. Samples from lithophysal cavities in the ESF and ECRB contain multiple populations of two-phase inclusions. Inclusion temperatures are highest in early calcite (\u3e 45 °C) and cooler in paragenetically younger early calcite, indicating cooling with time. The cooler temperatures coincide with temperatures recorded in the intensely fractured zone and indicate that secondary minerals in the intensely fractured zone began to precipitate later than secondary minerals in other locations. Freezing point depressions determined for inclusions range from -0.2 to -1.6 °C indicating trapping of a low salinity fluid. A small number of fluid inclusions in fluorite and quartz were identified and evaluated. Four inclusions in these minerals homogenized at temperatures higher than those recorded for calcite (91 ° - 95 °C) . Two approaches were used to constrain the timing of thermal fluids at Yucca Mountain. First, the age of MGSC was determined, and it provides a minimum age for fluids with elevated temperatures owing to the presence of only liquid-only inclusions in MGSC. Results indicate that MGSC began to precipitate across the site between 2.90 ± 0.06 Ma and about 1.95 ± 0.06 Ma, and MGSC has continued to precipitate to within the last half million years. These ages constrain fluids with elevated temperatures to have accessed the site more than about 2.90 Ma. Second, more precise temporal constraints were determined for samples in which datable opal or chalcedony occur in the intermediate or older parts of the mineral crusts, or are spatially related to 2-phase fluid inclusions. Such ages indicate that two-phase fluid inclusions are older than 5.32 ± 0.02 Ma, and that fluids with elevated temperatures were present at Yucca Mountain before this time. Results from this study are consistent with a model of descending meteoric water that infiltrated the cooling tuff sequence, became heated, and precipitated secondary minerals within the vadose zone. Fluid inclusions indicate that fluids with elevated temperatures were present during the early history of Yucca Mountain. Sparse, liquid-only fluid inclusions in late intermediate to young calcite indicate that secondary minerals were precipitated from low temperature fluids during the past 5 million years. This study demonstrates that the hypothesis of geologically recent upwelling hydrothermal fluids is untenable and should not disqualify Yucca Mountain as a potential nuclear waste storage site

Does the conditioned medium trigger the adipose-derived mesenchymal stem cells differentiation into Chondrocytes?

Background: Cartilage is an avascular tissue that has limited regenerative capacity. Stem cells, especiallymesenchymal stem cells (MSCs), have been regarded as a promising cell source for cartilage repair dueto their multi-lineage differentiation potential. Induction of mesenchymal stem cells into functional chondrocytesmay resolve the above problems in the cartilage repair. However, the imperative is to developeffective strategies for chondrogenic differentiation. The aim of this study is to evaluate if the induction ofadipose-derived mesenchymal stem cells (ADSCs) differentiation toward chondrocytes is possible withthe use of conditioned medium derived from chondrocytes culture. Material and methods: Conditioned medium (CM) from Normal chondrocyte cell line CRL 2648 was used to culture ADSCs, at the same time ADSCs with standard growth medium were used as a control. During this experiment, the phenotype was assessed using flow cytometry (CD90, CD44, CD45 and CD45), and Immunohistochemicalstaining was used to determine differentiation (anti-aggrecan, anti-CD15, anti-collagen II, anti-TRA-2-49). Results: ADSCs propagated rapidly in vitro and formed a homogenous fibroblast-like morphology. 0% of testedcells showed the expression of CD90 and CD44, while more than 90% did not reveal the expression ofCD34 and CD45. Results obtained in this study showed weak cytoplasmatic expression of aggrecanand alkaline phosphatase (TRA protein) and lack of CD151 expression. However, the majority of ADSCsexpanded with CM expressed type II collagen indicating that the chondrocyte-secreted factors inducedchondrogenic commitment during expansion. Conclusions: In the natural environment of living organisms, the chondrogenic differentiation of stem cells involve multiple signalling pathways. We can, to an extent mimic these signals in vitro however, for the clinicalpurposes it is very important to develop well-defined and efficient in vitro protocols. Our results indicatethat CM may regulate and induce differentiation of ADSCs into the chondrocyte lineage and can servealso as an in vitro model for studying specific lineage commitment

Improving inpatient medication adherence using attendant education in a tertiary care hospital in Uganda.

QUALITY PROBLEM: Although widely utilized in resource-rich health care systems, the use of quality improvement (QI) techniques is less common in resource-limited environments. Uganda is a resource-limited country in Sub-Saharan Africa that faces many challenges with health care delivery. These challenges include understaffing, inconsistent drug availability and inefficient systems that limit the provision of clinical care. INITIAL ASSESSMENT: Poor adherence to prescribed inpatient medications was identified as a key shortcoming of clinical care on the internal medicine wards of Mulago National Referral Hospital, Kampala, Uganda. Baseline data collection revealed a pre-intervention median inpatient medication adherence rate of 46.5% on the study ward. Deficiencies were also identified in attendant (lay caretaker) education, and prescriber and pharmacy metrics. CHOICE OF SOLUTION: A QI team led by a resident doctor and consisting of a QI nurse, a pharmacist and a ward nurse supervisor used standard QI techniques to address this issue. IMPLEMENTATION: Plan-Do-Study-Act cycle interventions focused on attendant involvement and education, physician prescription practices and improving pharmacy communication with clinicians and attendants. EVALUATION: Significant improvements were seen with an increase in overall medication adherence from a pre-intervention baseline median of 46.5% to a post-intervention median of 92%. Attendant education proved to be the most effective intervention, though resource and staffing limitations made institutionalization of these changes difficult. LESSONS LEARNED: QI methods may be the way forward for optimizing health care delivery in resource-limited settings like Uganda. Institutionalization of these methods remains a challenge due to shortage of staff and other resource limitations

Can bone marrow mesenchymal stem cells regenerate the myocardium?

Background: Cardiovascular diseases are the serious clinical problem, especially the loss of viable myocytes.A new approach, which provides a novel method for the treatment, is a tissue engineering andregenerative medicine. One of the current cell types used as a source to improve cardiac tissue repair,are MSCs. The aim of this study was to check if the 5’azacitidine and growth factors from cardiomyocytecell line initiate the differentiation of MSCs toward cardiomyocytes. Material and methods: Bone marrow MSCs were isolated and their biological features have been characterized.Conditioned media were prepared with the use of 5’azacitidine and growth factors releasedfrom cardiomyocytes. Results: The transdifferentiating process has been confirmed by the expression of specific muscle markers.Conditioned medium from cardiomyocyte cell line, as well as, 5’azacitidine induced muscle differentiationprocess in bone marrow MSCs in comparison to the control. Conclusions: Presented in this study data support the conclusion that this concept may represent a promisingstrategy for the repair of cardiac tissue, however, further experiments are necessary

Mineral chemistry of the Tissint meteorite: Indications of two-stage crystallization in a closed system

The Tissint meteorite is a geochemically depleted, olivine-phyric shergottite. Olivine megacrysts contain 300–600 μm cores with uniform Mg# (~80 ± 1) followed by concentric zones of Fe-enrichment toward the rims. We applied a number of tests to distinguish the relationship of these megacrysts to the host rock. Major and trace element compositions of the Mg-rich core in olivine are in equilibrium with the bulk rock, within uncertainty, and rare earth element abundances of melt inclusions in Mg-rich olivines reported in the literature are similar to those of the bulk rock. Moreover, the P Kα intensity maps of two large olivine grains show no resorption between the uniform core and the rim. Taken together, these lines of evidence suggest the olivine megacrysts are phenocrysts. Among depleted olivine-phyric shergottites, Tissint is the first one that acts mostly as a closed system with olivine megacrysts being the phenocrysts. The texture and mineral chemistry of Tissint indicate a crystallization sequence of: olivine (Mg# 80 ± 1) → olivine (Mg# 76) + chromite → olivine (Mg# 74) + Ti-chromite → olivine (Mg# 74–63) + pyroxene (Mg# 76–65) + Cr-ulvöspinel → olivine (Mg# 63–35) + pyroxene (Mg# 65–60) + plagioclase, followed by late-stage ilmenite and phosphate. The crystallization of the Tissint meteorite likely occurred in two stages: uniform olivine cores likely crystallized under equilibrium conditions; and a fractional crystallization sequence that formed the rest of the rock. The two-stage crystallization without crystal settling is simulated using MELTS and the Tissint bulk composition, and can broadly reproduce the crystallization sequence and mineral chemistry measured in the Tissint samples. The transition between equilibrium and fractional crystallization is associated with a dramatic increase in cooling rate and might have been driven by an acceleration in the ascent rate or by encounter with a steep thermal gradient in the Martian crust

Bulk rock composition and geochemistry of olivine-hosted melt inclusions in the Grey Porri Tuff and selected lavas of the Monte dei Porri volcano, Salina, Aeolian Islands, southern Italy.

The Aeolian Islands are an arcuate chain of submarine seamounts and volcanic islands, lying just north of Sicily in southern Italy. The second largest of the islands, Salina, exhibits a wide range of compositional variation in its erupted products, from basaltic lavas to rhyolitic pumice. The Monte dei Porri eruptions occurred between 60 ka and 30 ka, following a period of approximately 60,000 years of repose. The bulk rock composition of the Monte dei Porri products range from basaltic-andesite scoria to andesitic pumice in the Grey Porri Tuff (GPT), with the Monte dei Porri lavas having basaltic-andesite compositions. The typical mineral assemblage of the GPT is calcic plagioclase, clinopyroxene (augite), olivine (Fo72−84) and orthopyroxene (enstatite) ± amphibole and Ti-Fe oxides. The lava units show a similar mineral assemblage, but contain lower Fo olivines (Fo57−78). The lava units also contain numerous glomerocrysts, including an unusual variety that contains quartz, K-feldspar and mica. Melt inclusions (MI) are ubiquitous in all mineral phases from all units of the Monte dei Porri eruptions; however, only data from olivine-hosted MI in the GPT are reported here. Compositions of MI in the GPT are typically basaltic (average SiO2 of 49.8 wt %) in the pumices and basaltic-andesite (average SiO2 of 55.6 wt %) in the scoriae and show a bimodal distribution in most compositional discrimination plots. The compositions of most of the MI in the scoriae overlap with bulk rock compositions of the lavas. Petrological and geochemical evidence suggest that mixing of one or more magmas and/or crustal assimilation played a role in the evolution of the Monte dei Porri magmatic system, especially the GPT. Analyses of the more evolved mineral phases are required to better constrain the evolution of the magma

Fluid Inclusions in Astromaterials: Direct Samples of Early Solar System Aqueous Fluids

We have become increasingly aware of the fundamental importance of water, and aqueous alteration, on primitive solar-system bodies. All classes of astromaterials studied show some degree of interaction with aqueous fluids. We have direct observations of cryovolcanism of several small solar system bodies (e.g. Saturnian and Jovian moons), and indirect evidence for this process on the moons Europa, Titan, Ganymede, and Miranda, and the Kuiper Belt object Charon, and so are certain of the continuing and widespread importance of aqueous processes across the solar system. Nevertheless, we are still lacking fundamental information such as the location and timing of the aqueous alteration and the detailed nature of the aqueous fluid itself

Thermochronological evolution of calcite formation at the proposed Yucca Mountain repository site, Nevada: Part 1, secondary mineral paragenesis and geochemistry

In the near future a decision will be made as to whether or not Yucca Mountain, 90 miles northwest of Las Vegas, Nevada is a suitable site for a permanent, underground, high level nuclear waste repository. A major factor in determining the suitability of Yucca Mountain as a repository is the potential for the site to be flooded by water during the regulatory lifetime. The current study was undertaken to examine the past fluid history at the site, to gain a better understanding of the possibility of flooding in the near geologic future. To estimate the past fluid flux into the repository horizon, research has focused on secondary minerals that precipitated in open space in lithophysal cavities, fractures, and breccias in the host Miocene tuffs. U.S. Geological Survey researchers concluded that secondary minerals formed from descending surficial meteoric fluids in a vadose environment. State of Nevada scientists observed 2-phase fluid inclusions with homogenization temperatures of 35 to 85 °C in secondary minerals and concluded that these minerals formed in the phreatic environment from upwelling hydrothermal fluids. They further concluded that upwelling hydrothermal fluids repeatedly invaded the site, have invaded the site in the recent geologic past, and could do so again making Yucca Mountain an unsafe site for high level nuclear waste storage. These studies did not constrain the timing of incursion of the fluids with elevated temperatures or the extent of this fluid flux across the site. This report provides the geologic context for subsequent fluid inclusion and geochronological studies (Wilson et al., 2002) that identified the temperature and extent of the fluid incursion and placed absolute temporal constraints on the fluid history at Yucca Mountain. Here we describe a detailed paragenetic study that determined the depositional history of secondary minerals at Yucca Mountain. One hundred and fifty-five samples of secondary minerals were collected from lithophysal cavities, fractures, and breccias at Yucca Mountain. Extensive petrography, paragenetic studies, and microprobe mapping indicate that early secondary minerals were heterogeneously distributed across the site and consist of variable amounts of calcite, opal, chalcedony, fluorite, and quartz. Early calcite contained variable trace amounts of Mg (up to 1.3 wt. %). Intermediate minerals consist of mainly calcite, often in bladed habits, with minor opal, and chalcedony and quartz. These minerals contain no diagnostic trace element variations. The latest secondary minerals deposited across the site consist of sparry calcite and minor intergrown opal. This sparry calcite exhibits fine (~ 50 u.m) Mg-enriched and depleted growth zones and is chemically distinct from all other calcite. Mg-enriched growth-zoned sparry calcite (MGSC) contains up to ~ 1.0 wt. % Mg and has been identified in \u3e 65 % of the samples collected from across the site. MGSC and associated opal are always the paragenetically youngest minerals; where MGSC is not present, young secondary minerals did not precipitate. Calcite exhibits ranges for 513C from -8.5 %o to 9.5 %o, and for 818O from 5.2 %o to 22.1 %o. Samples exhibit generally consistent trends of decreasing C and increasing O isotopic compositions from paragenetically older to younger calcite. C and O isotope signatures for MGSC are between 16 %o and 20 %o for 618O and -3 %o and -8.5 %o for 513C. However, signatures for the various stages are not unique and are not diagnostic in correlating secondary mineral stages across the site. Early calcite is generally more luminescent than later calcite, but luminescence was not sufficiently consistent to aid in constraining the paragenetic sequence. LA-ICP-MS analyses indicate that higher levels of U, Th, and Sr are locally present in MGSC compared to paragenetically early calcite, however, this variation is not present in all samples. An important observation is that 90% of primary and secondary open space in the tuffs at Yucca Mountain contains no secondary mineral record. Where secondary minerals are present, the older secondary mineral record is heterogeneous across the site. However, MGSC, which forms the youngest part of the secondary mineral record, is present in a majority of samples and exhibits a more homogeneous distribution across the site. Secondary mineral abundances and textures indicate that secondary minerals precipitated in a vadose environment. The observed features are not consistent with secondary mineral precipitation in a phreatic environment saturated with aqueous fluids. Growth zoning in the outermost MGSC is consistent with formation from discontinuous influx of small fluid volumes with variable Mg content from surficial fluids that percolated downwards. Fluctuations in the Mg content in MGSC may be related to climate changes that occurred in the last few million years