Thermal History of the Ecstall Pluton from \u3csup\u3e40\u3c/sup\u3eAr/\u3csup\u3e39\u3c/sup\u3eAr Geochronology and Thermal Modeling

New 40Ar/39Ar thermochronology results and thermal modeling support the hypothesis of Hollister et al. (2004), that reheating of the mid-Cretaceous Ecstall pluton by intrusion of the Coast Mountains Batholith (CMB) was responsible for spatially variable remagnetization of the Ecstall pluton. 40Ar/39Ar ages from hornblende and biotite from 12 locations along the Skeena River across the northern part of the Ecstall pluton decrease with proximity to the Quottoon plutonic complex, the nearest member of the CMB to the Ecstall pluton. The oldest 40Ar/39Ar ages are found farthest from the Quottoon plutonic complex, and are 90 ± 3 Ma for hornblende, and 77.9 ± 1.2 Ma for biotite. The youngest40Ar/39Ar ages are found closest to the Quottoon plutonic complex, and are 51.6 ± 1.2 Ma for hornblende, and 45.3 ± 1.7 Ma for biotite. No obvious relationship between grain size and age is seen in the Ecstall pluton biotites. Spatial trends in 40Ar/39Ar ages are consistent with model results for reheating by a thermal wall at the location of the Quottoon plutonic complex. Although no unique solution is suggested, our results indicate that the most appropriate thermal history for the Ecstall pluton includes both reheating and northeast side up tilting of the Ecstall pluton associated with intrusion of the Quottoon plutonic complex. Estimates of northward translation from shallow paleomagnetic inclinations in the western part of the Ecstall pluton are reduced to ∼3000 km, consistent with the Baja-BC hypothesis, when northeast side up tilting is accounted for

Single grain (U-Th)/He ages from phosphates in Acapulco meteorite and implications for thermal history

The cooling history of the Acapulco meteorite for >400°C is well established using various chronometers suggesting extremely fast cooling (>1000°C/Ma). In contrast, the thermal history for low temperatures (<400°C) is poorly understood because of large uncertainties in the chronometers applicable to this temperature range. To better constrain the cooling history for the low-temperature range, we applied (U–Th)/He dating techniques to individual phosphate grains. One whitlockite and 11 apatite grains yielded (U–Th)/He ages ranging from 1272±22 (1σ, analytical error only) Ma to 4584±51 Ma, with tight clustering at ∼4.55 Ga. The weighted mean of the five oldest ages (4538±32 Ma, 1σ uncertainty including systematic error) is suggested to be the minimum age representing primary cooling of the Acapulco body passing through ∼120°C. Although it is impossible to precisely quantify the effects of energetic α particle ejection from the outermost ∼20 μm of the phosphates, petrographic evidence suggests that most dated samples are fragments likely derived from the interior of larger grains, thus greatly reducing this source of error. Indeed the five oldest samples cannot have suffered substantial ejection since the uncorrected ages are identical with the crystallization age of the Acapulco meteorite. The new (U–Th)/He data suggest rapid cooling of Acapulco down to ∼120°C. This evidence suggests that the younger ^(40)Ar/^(39)Ar age (4507±9 (1σ) Ma) obtained from Acapulco plagioclase, which should reflect cooling through ∼300°C, is spuriously young due to systematic errors (i.e., decay constants and/or standard data) in the ^(40)Ar/^(39)Ar method, as suggested by comparison between high-precision ^(40)Ar/^(39)Ar and U/Pb ages for terrestrial volcanic rocks. The scattered He age distribution <4.0 Ga implies very heterogeneous thermal disturbances after the primary cooling of the body

Trapped Ar isotopes in meteorite ALH 84001 indicate Mars did not have a thick ancient atmosphere

Water is not currently stable in liquid form on the martian surface due to the present mean atmospheric pressure of ∼7 mbar and mean global temperature of ∼220 K. However, geomorphic features and hydrated mineral assemblages suggest that Mars’ climate was once warmer and liquid water flowed on the surface. These observations may indicate a substantially more massive atmosphere in the past, but there have been few observational constraints on paleoatmospheric pressures. Here we show how the [superscript 40]Ar/[superscript 36]Ar ratios of trapped gases within martian meteorite ALH 84001 constrain paleoatmospheric pressure on Mars during the Noachian era [∼4.56–3.8 billion years (Ga)]. Our model indicates that atmospheric pressures did not exceed ∼1.5 bar during the first 400 million years (Ma) of the Noachian era, and were <400 mbar by 4.16 Ga. Such pressures of CO[subscript 2] are only sufficient to stabilize liquid water on Mars’ surface at low latitudes during seasonally warm periods. Other greenhouse gases like SO[superscript 2] and water vapor may have played an important role in intermittently stabilizing liquid water at higher latitudes following major volcanic eruptions or impact events.United States. National Aeronautics and Space Administration. Mars Fundamental Research Program (Grant MFRP05-0108)Ann and Gordon Getty Foundatio

Towards Designing an Integrated Earth Observation System for the Provision of Solar Energy Resource and Assessment

The GEOSS strategic plan specifically targets the area of improved energy resource management due to the importance of these to the economic and social viability of every nation of the world. With the world s increasing demand for energy resources, the need for new alternative energy resources grows. This paper overviews a new initiative within the International Energy Agency that addresses needs to better manage and develop solar energy resources worldwide. The goal is to provide the solar energy industry, the electricity sector, governments, and renewable energy organizations and institutions with the most suitable and accurate information of the solar radiation resources at the Earth's surface in easily-accessible formats and understandable quality metrics. The scope of solar resource assessment information includes historic data sets and currently derived data products using satellite imagery and other means. Thus, this new task will address the needs of the solar energy sector while at the same time will serve as a model that satisfies GEOSS objectives and goals

A crystal/melt partitioning study for sulfur and halogens: pyroxenes as probes for assessing gas loads in LIP magmas

A link between magmatism from Large Igneous Provinces (LIPs) and mass extinctions has been observed at leastin five occasions in the Phanerozoic. Volatile species such as S, C and halogen compounds severely impactedthe global environment, released both from melts and thermal metamorphism of volatile-rich sediments. It is stillchallenging to obtain quantitative estimates of the degassed volatiles for ancient magmatic systems, particularly inthe absence of melt inclusions. We propose to fill the gap of knowledge on sulfur partitioning between mineralsand melts, at the aim of using phenocrysts as probes of volatile contents in the melts from which they crystallized.Measuring a volatile concentration in natural minerals (chiefly clinopyroxene) and combining it with an experi-mentally determined partition coefficient (KD), the volatile load in basaltic equilibrium melts can be calculated.We measured a clinopyroxene/melt sulfur KD of 0.0009\ub10.0001 for basaltic experiments performed at conditionstypical of LIP basalts (FMQ-2; 800-1000 MPa; 1000 \u30a-1350 \u30aC), through ion microprobe (Nordsim). Basaltic ex-periments were also simultaneously analyzed for Cl and F. For these elements the measured clinopyroxene/meltKDs were more variable, 0.0071\ub10.0052 and 0.1985\ub10.087, respectively. Compatibility of sulfur, chlorine andfluorine in clinopyroxene from basaltic systems is markedly different (F>Cl>S), in agreement with what observedby previous studies, and the partition coefficient is well constrained around 0.001 for S. Application of the newlymeasured sulfur KD to samples from thoroughly-dated lava piles from the Deccan Traps and from the SiberianTraps sills reveal that most of the basalts were at or near sulfide saturation (up to ca. 2000 ppm for low fO2melts)

IUGS–IUPAC recommendations and status reports on the half-lives of 87 Rb, 146 Sm, 147 Sm, 234 U, 235 U, and 238 U (IUPAC Technical Report)

The IUPAC–IUGS joint Task Group “Isotopes in Geosciences” (TGIG) has evaluated the published literature on the half-lives of six long-lived, geologically relevant radioactive nuclides. Where conflicting literature estimates are present, it is necessary to first identify any systematic bias in accordance with metrological traceability and to exclude the biased estimates from further consideration. The TGIG recommends three robust half-life estimates: 49.61±0.16 Ga for 87Rb, corresponding to a decay constant λ(87Rb) = (1.3972±0.0045)×10–11 a–1; 106.25±0.38 Ga for 147Sm, and a corresponding decay constant λ(147Sm) = (6.524±0.024)×10–12 a–1; 4.4683±0.0096 Ga for 238U, i.e. a decay constant λ(238U) = (1.55125±0.00333)×10–10 a–1. All cited uncertainties have a coverage factor k = 2. For other radionuclides of Sm and U no unambiguous consensus value can be endorsed at present by TGIG, which limits its evaluation to a status report highlighting unaccounted-for potential sources of bias. The improved repeatability of mass spectrometric measurements has revealed systematic bias effects that had been dismissed as subordinate in the past. These issues can only be resolved by future dedicated investigations

Crustal shortening, exhumation, and strain localization in a collisional orogen: the Bajo Pequeño Shear Zone, Sierra de Pie de Palo, Argentina

The Bajo Pequeño Shear Zone (BPSZ) is a lower-crustal shear zone that records shortening and exhumation associated with the establishment of a new plate boundary, and its placement in a regional structural context suggests that local- to regional-scale strain localization occurred with progressive deformation. A kilometer-scale field and analytical cross section through the ~80 m thick BPSZ and its adjacent rocks indicates an early Devonian (405–400 Ma) phase of deformation on the western margin of Gondwanan continental crust. The earliest stages of the BPSZ, recorded by metamorphic and microstructural data, involved thrusting of a hotter orthogneiss over a relatively cool pelitic unit, which resulted in footwall garnet growth and reset footwall white mica 40Ar/39Ar ages in proximity to the shear zone. Later stages of BPSZ activity, as recorded by additional microstructures and quartz c-axis opening angles, were characterized by strain localization to the center of the shear zone coincident with cooling and exhumation. These and other data suggest that significant regional tectonism persisted in the Famatinian orogenic system for 60–70 million years after one microplate collision (the Precordillera) but ceased 5–10 million years prior to another (Chilenia). A survey of other synchronous structures shows that strain was accommodated on progressively narrower structures with time, indicating a regional pattern of strain localization and broad thermal relaxation as the Precordillera collision evolved.Fil: Garber, Joshua M.. University of California at Davis; Estados UnidosFil: Roeske, Sarah M.. University of California at Davis; Estados UnidosFil: Warren, Jessica. University of Stanford; Estados UnidosFil: Mulcahy, Sean R.. University of California at Berkeley; Estados UnidosFil: McClelland, William C.. University of Iowa; Estados UnidosFil: Austin, Lauren J.. University of Oregon; Estados UnidosFil: Renne, Paul R.. University of California at Berkeley; Estados UnidosFil: Vujovich, Graciela Irene. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Laboratorio de Tectónica Andina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Time-related variation of volatile contents of Western Ghats volcanic formations, Deccan, India

Deccan volcanism in India covered more than 1 million square km and reached a maximum thickness of about 3 km, as presently preserved in the Western Ghats volcanic lava piles. Volcanic activity started at about 66.4 Ma (Jawhar formation) and ended at about 65.5 Ma (Mahabaleshwar unit; Renne et al., 2015). Deccan volcanism straddled the Cretaceous-Paleogene boundary (ca. 66.0 Ma) and possibly contributed to the end-Cretaceous mass extinction event through emission of gases such as SO2, CO2, Cl, F that may have triggered global climate changes. Severe pollution by volcanic gases is supported by the high S and Cl contents (up to 1400 and up to 900 ppm, respectively; Self et al., 2008) measured in a few olivine- and plagioclase-hosted melt inclusions from the Jawhar, Neral, and Thakurvadi Formations (early lava flows, ca. 66.3-66.4 \ub1 0.1 Ma; Renne et al., 2015) and by magmatic S contents (up to 1800 ppm; Callegaro et al., 2014) calculated from S measurements in clinopyroxenes from the Mahabaleshwar unit (ca. 65.5 \ub1 0.1; Schoene et al., 2015). Here, we present new analyses of S, Cl, and F, obtained by ion-probe and synchrotron light micro-fluorescence analyses on clinopyroxenes and plagioclase phenocrysts from ?al? lava flow units of the Western Ghats. The volatile contents of the host magmas have been calculated from recently published clinopyroxene/basalt partition coefficients. These new data will describe the time-related variation of volatile elements hosted and eventually emitted by Deccan lavas and shed light on their environmental impact. References: Callegaro S. et al. (2014). Geology 42, 895-898. Renne P.R. et al. (2015). Science 350, 76-78. Schoene B. et al. (2015). Science 347, 192-184. Self S. et al. (2008). Science 319, 1654-1657

40Ar/39Ar ages for deep (~3.3 km) samples from the Hawaii Scientific Drilling Project, Mauna Kea volcano, Hawaii

The Hawaii Scientific Drilling Project recovered core from a 3.5 km deep hole from the flank of MaunaKea volcano, providing a long, essentially continuous record of the volcano’s physical and petrologicdevelopment that has been used to infer the chemical and physical characteristics of the Hawaiian mantle plume. Determining a precise accumulation rate via 40Ar/39Ar dating of the shield-stage tholeiites, which constitute 95–98% of the volcano’s volume is challenging. We applied 40Ar/39Ar dating using laser- and furnace-heating in two laboratories (Berkeley and Curtin) to samples of two lava flows from deep in the core (~3.3 km). All determinations yield concordant isochron ages, ranging from 612 +/- 159 to 871 +/- 302 ka (2delta; with P = 0.90). The combined data yield an age of 681 +/- 120 ka (P = 0.77) for pillow lavas near the bottom of the core. This new age, when regressed with 40Ar/39Ar isochron ages previously obtained for tholeiites higher in the core, defines a constant accumulation rate of 8.4 +/- 2.6 m/ka that can be used to interpolate the ages of the tholeiites in the HSDP core with a mean uncertainty of about 83 ka. For example at ~3300 mbsl, the age of 664 +/- 83 ka estimated from the regression diverges at the 95% confidence level from the age of 550 ka obtained from the numerical model of DePaolo and Stolper (1996). The new data have implications for the timescale of the growth of Hawaiian volcanoes, the paleomagnetic record in the core, and the dynamics of the Hawaiian mantle plume