| 1. |
- Abolfathi, Bela, et al.
(author)
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The Fourteenth Data Release of the Sloan Digital Sky Survey : First Spectroscopic Data from the Extended Baryon Oscillation Spectroscopic Survey and from the Second Phase of the Apache Point Observatory Galactic Evolution Experiment
- 2018
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In: Astrophysical Journal Supplement Series. - : IOP Publishing Ltd. - 0067-0049 .- 1538-4365. ; 235:2
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Journal article (peer-reviewed)abstract
- The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in operation since 2014 July. This paper describes the second data release from this phase, and the 14th from SDSS overall (making this Data Release Fourteen or DR14). This release makes the data taken by SDSS-IV in its first two years of operation (2014-2016 July) public. Like all previous SDSS releases, DR14 is cumulative, including the most recent reductions and calibrations of all data taken by SDSS since the first phase began operations in 2000. New in DR14 is the first public release of data from the extended Baryon Oscillation Spectroscopic Survey; the first data from the second phase of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2), including stellar parameter estimates from an innovative data-driven machine-learning algorithm known as "The Cannon"; and almost twice as many data cubes from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous release (N = 2812 in total). This paper describes the location and format of the publicly available data from the SDSS-IV surveys. We provide references to the important technical papers describing how these data have been taken (both targeting and observation details) and processed for scientific use. The SDSS web site (www.sdss.org) has been updated for this release and provides links to data downloads, as well as tutorials and examples of data use. SDSS-IV is planning to continue to collect astronomical data until 2020 and will be followed by SDSS-V.
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| 2. |
- Barnes, C. J., et al.
(author)
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Exhumation of the High-Pressure Tsakkok Lens, Swedish Caledonides : Insights From the Structural and White Mica(40)Ar/Ar-39 Geochronological Record
- 2020
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In: Tectonics. - : American Geophysical Union (AGU). - 0278-7407 .- 1944-9194. ; 39:7
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Journal article (peer-reviewed)abstract
- Integrated structural, geochemical, and geochronological investigations were conducted on metasedimentary rocks in the eclogite-bearing Tsakkok Lens of the Seve Nappe Complex (Scandinavian Caledonides) to resolve its exhumation history. Three deformation events are defined. D1 is likely related to the prograde to peak-metamorphic stages, represented by a locally preserved S1. D2 resulted in vertical shortening and is defined by a pervasive S2 and cm-/m-scale F2 closed folds. D2 terminated with Scandian thrusting, which emplaced the overlying Koli Nappe Complex. D3 records NE-SW shortening and constitutes m-/km-scale F3 open folds that deformed the Tsakkok Lens and Koli Nappe Complex together. In situ white mica(40)Ar/Ar-39 geochronology was conducted on select metasedimentary samples possessing S1 or S2 to resolve the timing of exhumation. Postdecompression cooling of the Tsakkok Lens is best recorded by samples containing S1 or S2 that yield homogeneous white mica chemistry and(40)Ar/Ar-39 dates. The timing of cooling is resolved to 477.2 +/- 4.1 Ma (S1) and 475.3 +/- 3.5 Ma (S2). Vertical shortening of the lens during exhumation may have proceeded until 458.1 +/- 9.0 Ma. Later-stage deformation during Scandian thrusting penetrated the Tsakkok Lens at 429.9 +/- 9.0 Ma, or younger. This resulted in noncoaxial deformation of the metasedimentary rocks, producing heterogeneous white mica chemistry and partially reset the older(40)Ar/Ar-39 cooling record. Temperatures for deformation are resolved to the upper greenschist-lower amphibolite facies. Altogether, the Tsakkok Lens records rapid exhumation from eclogite-facies conditions to midcrustal depths or shallower, followed by emplacement of the overlying Koli Nappe Complex.
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| 3. |
- Barnes, C. J., et al.
(author)
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Using Th-U-Pb geochronology to extract crystallization ages of Paleozoic metamorphic monazite contaminated by initial Pb
- 2021
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In: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 582
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Journal article (peer-reviewed)abstract
- Geochronology of Th-rich minerals is advantageous as it allows use of three isotopic systems (i.e., Pb-206/U-238, Pb-207/U-235, and Pb-208/Th-232) for accurate data assessment. The Pb-208/Th-232 system is especially advantageous in cases where the dated mineral includes an initial Pb component, as Pb-208/Th-232 is the least sensitive to the effects of initial Pb amongst the three systems. This benefit is demonstrated with monazite from a white mica schist of the Tsakkok Lens, Scandinavian Caledonides, where three distinct generations of Paleozoic monazite (Mnzsingle bondI, Mnz-II, Mnz-III) are recognized and dated using laser ablation inductively coupled mass spectrometry. The generations are interpreted to represent monazite crystallization in high-pressure conditions (Mnzsingle bondI), followed by lower-pressure monazite growth (Mnz-II), and likely dissolution-reprecipitation of the pre-existing monazite (Mnz-III). The results are compared in Tera-Wasserburg, Wetherill, and Th-U-Pb concordia space for each monazite generation. In both Tera-Wasserburg and Wetherill space, the data are all discordant and indicate an initial Pb component in the monazite. The trend and magnitude of discordance due to initial Pb in Mnz-I and Mnz-II is generally controlled by UO2 content of the monazite, with higher UO2 equating to greater radiogenic Pb and a dampening of the initial Pb effect, which is most prominent in the Pb-207/U-235 system. For the same generations, initial Pb discordance of Pb-206/U-238 versus Pb-208/Th-232 is less apparent due to the insensitivity of Pb-208/Th-232. Mnz-III does not follow the initial Pb trends, likely due to disturbance of the chemical and isotopic systems during recrystallization. Additional discordance in Mnz-I and Mnz-II, which is not related to initial Pb, is recognized and increases with actinide content. The additional discordance may be due to Pb-mobilization in Mnz-I and Mnz-II domains and is revealed when utilizing the( 208)Pb/Th-232 system due to its insensitivity to initial Pb effects. Consequently, relying only on the U-Pb systems can lead to significant initial Pb overcorrections in Tera-Wasserburg or Wetherill concordia space and to calculations of erroneously young concordia dates. The Th-U-Pb concordia method, incorporating all three systems, does not require an initial Pb correction and, therefore, can account for the additional discordance. The Th-U-Pb concordia dates are interpretated as accurate crystallization ages for Mnz-I (484.7 +/- 1.1 Ma, MSWD: 1.4) and Mnz-II (474.7 +/- 1.2 Ma, MSWD: 1.9). The timing for Mnz-III formation is not well-resolved as it formed via result of dissolution-reprecipitation of the pre-existing monazite, likely under lower amphibolite- to greenschist-facies conditions.
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| 4. |
- Blanton, Michael R., et al.
(author)
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Sloan Digital Sky Survey IV : Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
- 2017
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In: Astronomical Journal. - : IOP Publishing Ltd. - 0004-6256 .- 1538-3881. ; 154:1
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Journal article (peer-reviewed)abstract
- We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and. high signal-to-noise ratios in the near-infrared. The Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey is obtaining spatially resolved spectroscopy for thousands of nearby galaxies (median z similar to 0.03). The extended Baryon Oscillation Spectroscopic Survey (eBOSS) is mapping the galaxy, quasar, and neutral gas distributions between z similar to 0.6 and 3.5 to constrain cosmology using baryon acoustic oscillations, redshift space distortions, and the shape of the power spectrum. Within eBOSS, we are conducting two major subprograms: the SPectroscopic IDentification of eROSITA Sources (SPIDERS), investigating X-ray AGNs. and galaxies in X-ray clusters, and the Time Domain Spectroscopic Survey (TDSS), obtaining spectra of variable sources. All programs use the 2.5 m Sloan Foundation Telescope at the. Apache Point Observatory; observations there began in Summer 2014. APOGEE-2 also operates a second near-infrared spectrograph at the 2.5 m du Pont Telescope at Las Campanas Observatory, with observations beginning in early 2017. Observations at both facilities are scheduled to continue through 2020. In keeping with previous SDSS policy, SDSS-IV provides regularly scheduled public data releases; the first one, Data Release 13, was made available in 2016 July.
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