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Calvin F Miller - One of the best experts on this subject based on the ideXlab platform.
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porphyry cu formation in the middle jurassic yerington batholith nevada usa constraints from laser raman trace element u pb age and oxygen isotope analyses of zircon
Geosphere, 2017Co-Authors: Tenley J Banik, Matthew A Coble, Calvin F MillerAbstract:Porphyry copper systems provide the majority of global copper resources and are generally formed from highly oxidized magmas. Zircon, a common Accessory Mineral in granitoid rocks that host porphyry deposits, is well established as an effective tool for assessing timescales and evolution of magmatic conditions. We present new U-Pb ages, trace element concentrations, and oxygen isotope ratios of zircon measured by secondary ion mass spectrometry (SIMS) from a suite of cogenetic host rocks and ore-bearing porphyry dikes from the Yerington copper mine, western Nevada, USA. Zircons were subjected to chemical abrasion and thermal annealing in order to evaluate Pb loss, and laser Raman analyses were performed to avoid measurements of radiation damaged or non-crystalline (potentially metamict) portions of zircon. Weighted-mean U-Pb ages from ore-bearing Yerington porphyry dikes and granitoid host plutons overlap at 2σ uncertainty, ranging from 168.7 ± 1.1 Ma to 170.0 ± 1.4 Ma. Zircon trace element concentrations show fractional crystallization trends, such as decreasing Ti versus increasing Eu anomaly (Eu N /Eu N *) and Yb/Gd. Uranium concentrations range from 90 to 2200 ppm (average is ~320 ppm U), Eu-anomaly ratios range from 0.19 to 1.05, and Ce N /Ce N * values range from 20 to 980. Oxygen isotope compositions range from 4.8 ± 0.7‰ to 5.7 ± 0.8‰ (sample means), with the most depleted composition from the youngest porphyry dike. We find no statistically significant difference in ages, trace elements, or oxygen isotopes from chemically abraded and untreated zircons. Based on variations in magmatic conditions as suggested by Eu anomalies, trace element trends, model zircon crystallization temperatures, and δ 18 O in zircon, we conclude that variable but increasing oxidation and ongoing fractional crystallization were strong controls on elemental partitioning and ore-forming processes in the Yerington system.
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the evolution of the peach spring giant magma body evidence from Accessory Mineral textures and compositions bulk pumice and glass geochemistry and rhyolite melts modeling
Journal of Petrology, 2013Co-Authors: Ayla S Pamukcu, Tamara L Carley, Calvin F Miller, Guilherme A R Gualda, Charles A FergusonAbstract:The Miocene Peach Spring Tuff is a giant (� 640 km 3 dense rock equivalent) pyroclastic deposit that is extensively exposed in the southwestern USA. Evidence from geochemical and textural analyses of bulk-rocks, glasses, and Accessory Minerals (zircon, titanite, allanite, chevkinite, magnetite) from outflow and intra-caldera pumice clasts and fiamme, in combination with field observations and rhyolite-MELTS modeling, suggests that the Peach Spring magma body was compositionally and thermally zoned with a basal cumulate, and that it crystallized over millennial timescales before being remobilized by mafic input prior to erupting. Crystal contents, bulk compositions, spatial distributions, and temperatures (recorded by Ti in zircon and Zr in titanite) of pumice clasts and fiamme vary systematically: distal outflow high-silica rhyolites are crystal-poor and document lower temperatures; intra-caldera trachytes are crystal-rich and record higher temperatures. These variations indicate that the Peach Spring magma body was zoned. We interpret the outflow high-silica rhyolites to represent the first portion of the magma body to erupt. Zircon and titanite display core-to-edge reductions in rare earth element (REE) concentration and temperature, suggestive of relatively uninterrupted crystallization as the magma body cooled; crystallization temperature intervals from rhyoliteMELTS are consistent with those recorded by zircon and titanite. Exponential size distributions for Accessory Minerals and phenocryst textures are consistent with geochemical evidence for a simple cooling and crystallization history. Intra-caldera trachytes and outflow low-silica rhyolites represent the later portion of the magma body to erupt.This magma experienced a late-stage heating event potentially associated with the onset of the eruption.The edges of titanite crystals are enriched in REE and Zr, and zircon edges are enriched in Ti, suggesting higher temperatures during edge crystallization (at least 9008C). Concave-down crystal size distributions and resorption features on phenocrysts are additional signs of heating. Rare trachyandesite enclaves and the presence of mafic to intermediate lavas immediately underlying the Peach Spring Tuff suggest that a mafic magma input may have been the cause of the heating. Evidence further suggests that the intra-caldera trachytes may represent a remobilized cumulate at the base of the magma body, which retained some melt prior to rejuvenation. Bulk pumice and fiamme compositions are very rich in feldspar and Accessory Mineral phenocrysts, indicative of accumulation of these Minerals; high crystal contents (� 35%) and evidence of heating and resorption imply that this magma was even more crystal-rich prior to the heating event. Rhyolite-MELTS simulations suggest that the trachyte magma had roughly 1wt % water, which cannot be totally accounted for by hydrous phases, thus requiring some amount of melt within the cumulate. Kinked magnetite size distributions are interpreted to represent a change from growth-dominated crystallization (larger crystals, shallow slopes) to nucleation-dominated (small crystals, steep slopes) owing to the onset of eruptive decompression. Timescales of magnetite crystallization calculated from these slopes indicate that the Peach Spring magma body crystallized over millennial timescales, and that eruptive decompression began 10 � 1 ^10 2 years prior to eruption.
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the evolution of the peach spring giant magma body evidence from Accessory Mineral textures and compositions bulk pumice and glass geochemistry and rhyolite melts modeling
Journal of Petrology, 2013Co-Authors: Ayla S Pamukcu, Tamara L Carley, Calvin F Miller, Guilherme A R Gualda, Charles A FergusonAbstract:The Miocene Peach Spring Tuff is a giant (� 640 km 3 dense rock equivalent) pyroclastic deposit that is extensively exposed in the southwestern USA. Evidence from geochemical and textural analyses of bulk-rocks, glasses, and Accessory Minerals (zircon, titanite, allanite, chevkinite, magnetite) from outflow and intra-caldera pumice clasts and fiamme, in combination with field observations and rhyolite-MELTS modeling, suggests that the Peach Spring magma body was compositionally and thermally zoned with a basal cumulate, and that it crystallized over millennial timescales before being remobilized by mafic input prior to erupting. Crystal contents, bulk compositions, spatial distributions, and temperatures (recorded by Ti in zircon and Zr in titanite) of pumice clasts and fiamme vary systematically: distal outflow high-silica rhyolites are crystal-poor and document lower temperatures; intra-caldera trachytes are crystal-rich and record higher temperatures. These variations indicate that the Peach Spring magma body was zoned. We interpret the outflow high-silica rhyolites to represent the first portion of the magma body to erupt. Zircon and titanite display core-to-edge reductions in rare earth element (REE) concentration and temperature, suggestive of relatively uninterrupted crystallization as the magma body cooled; crystallization temperature intervals from rhyoliteMELTS are consistent with those recorded by zircon and titanite. Exponential size distributions for Accessory Minerals and phenocryst textures are consistent with geochemical evidence for a simple cooling and crystallization history. Intra-caldera trachytes and outflow low-silica rhyolites represent the later portion of the magma body to erupt.This magma experienced a late-stage heating event potentially associated with the onset of the eruption.The edges of titanite crystals are enriched in REE and Zr, and zircon edges are enriched in Ti, suggesting higher temperatures during edge crystallization (at least 9008C). Concave-down crystal size distributions and resorption features on phenocrysts are additional signs of heating. Rare trachyandesite enclaves and the presence of mafic to intermediate lavas immediately underlying the Peach Spring Tuff suggest that a mafic magma input may have been the cause of the heating. Evidence further suggests that the intra-caldera trachytes may represent a remobilized cumulate at the base of the magma body, which retained some melt prior to rejuvenation. Bulk pumice and fiamme compositions are very rich in feldspar and Accessory Mineral phenocrysts, indicative of accumulation of these Minerals; high crystal contents (� 35%) and evidence of heating and resorption imply that this magma was even more crystal-rich prior to the heating event. Rhyolite-MELTS simulations suggest that the trachyte magma had roughly 1wt % water, which cannot be totally accounted for by hydrous phases, thus requiring some amount of melt within the cumulate. Kinked magnetite size distributions are interpreted to represent a change from growth-dominated crystallization (larger crystals, shallow slopes) to nucleation-dominated (small crystals, steep slopes) owing to the onset of eruptive decompression. Timescales of magnetite crystallization calculated from these slopes indicate that the Peach Spring magma body crystallized over millennial timescales, and that eruptive decompression began 10 � 1 ^10 2 years prior to eruption.
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record of magma chamber processes preserved in Accessory Mineral assemblages aztec wash pluton nevada
American Mineralogist, 1999Co-Authors: Delores M Robinson, Calvin F MillerAbstract:Field relations and geochemistry indicate that Aztec Wash pluton had a complex, open-system history. The tilted pluton represents a 2.5 km thick chamber that was recharged with both felsic and mafic magma. The lower portion is highly heterogeneous, with mafic sheets; cumulates; hybrid rocks; mafic, felsic, and composite dikes; and sheets and pods of granite (heterogeneous [H] zone). The upper part is granite that is generally homogeneous in texture and geochemistry (granite [G] zone). At the base of the G zone, a discontinuous zone (buffer [B] zone) records interaction between the G and H zones. Complexity of the H zone makes detailed reconstruction of magma chamber history difficult, and the relatively homogeneous G zone appears to offer few clues about the evolution of the pluton or the interaction between the felsic and underlying more mafic magmas. Accessory Mineral textures, zoning, and assemblages in the G zone, however, are far from homogeneous and provide clear evidence for fluctuating conditions that elucidates magma chamber history. Mafic rocks of the H zone contain the Accessory Mineral assemblage ilmenite+magnetite+quench apatite+ or -late sphene and zircon. G zone rocks have magnetite+apatite+sphene+zircon+ or -allanite, ilmenite, and chevkinite. The magnetite+allanite+early sphene, apatite, and zircon association that characterizes much of the G zone indicates a lower temperature and possibly higher f O2 than the H zone assemblage. Mineral textures and zoning, however, document fluctuations in the stable G zone assemblage: (1) as many as five rounded surfaces truncate internal zones in zircon, each indicating a dissolution event; (2) in addition to euhedral concentric zoning, sphene contains regions of highly irregular zoning that are rich in inclusions, especially anhedral ilmenite; (3) ilmenite and allanite are mutually exclusive, but allanite is present in the matrix of rocks that contain sphene with ilmenite inclusions, and sphene grains in some samples have alternating regions with allanite and ilmenite inclusions. We attribute fluctuations in the stable G zone Accessory assemblage to fluctuations in temperature and possibly f O2 , with appearance of the high-T, reduced assemblage indicating interaction with hot, mafic, H zone magma. These interactions certainly involve heat transfer and may involve limited chemical contamination. We infer that they must have taken place near the H zone-G zone boundary. The most frequent and intense fluctuations (marked by zircon with the highest number of truncation surfaces, and by sphene with irregular zoning and abundant ilmenite inclusions) affected rocks that are near the boundary, but ilmenite inclusions in sphene and truncation surfaces in zircon are present to the top of the pluton. We conclude that granitic magma was subjected to multiple cycles of thermally induced vertical transfer-convection-that, at least initially, affected the entire upper part of the chamber.
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Accessory Mineral behavior during differentiation of a granite suite monazite xenotime and zircon in the sweetwater wash pluton southeastern california u s a
Chemical Geology, 1993Co-Authors: D Wark, Calvin F MillerAbstract:Abstract Compositional and textural characteristics of the Accessory Minerals monazite, xenotime and zircon in the Sweetwater Wash granites and related aplites indicate that these phases not only controlled much of the trace-element geochemistry of the suite, but that they also record the melt compositional changes that occurred during magmatic differentiation. Fractionation of monazite due to decreasing saturation levels of its essential structural constituents with falling temperature was likely responsible for an ongoing trend of light rare-earth element (REE) depletion. This was accompanied by increasing heavy-REE concentrations until xenotime joined the crystallizing assemblage; subsequently, combined monazite-xenotime fractionation resulted in lowering of the entire REE budget. Zircon, which contains inherited cores that were apparently resorbed and rounded during initial anatexis, was saturated throughout the differentiation history of the Sweetwater Wash suite. Accessory phases in granite and aplite exhibit strong compositional differences at a variety of scales. The differences are best displayed by monazite: on average, crystals in more differentiated rocks (aplites) are relatively depleted in light REE's and contain higher concentrations of the substituting elements U and Th. Zircon displays complimentary increases in Hf and Y, while xenotime shows a slight increase in Th and in Gd/Ho ratios; both phases also exhibit higher U concentrations in aplites than in granites. These differences in Accessory Mineral compositions are observed not only between granites and the more differentiated aplites, but also within individual thin sections, due to in situ fractionation. On an even smaller scale, strong compositional variations are present within single crystals, possibly due to diffusion-controlled melt-compositional gradients in the regions (a) adjacent to growing major phases, and (b) adjacent to the growing Accessory crystal itself. Our observations indicate that compositional variations among Accessory Minerals are potentially useful for tracking of magmatic processes, but that the scale of observed variations must be carefully considered.
Charles A Ferguson - One of the best experts on this subject based on the ideXlab platform.
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the evolution of the peach spring giant magma body evidence from Accessory Mineral textures and compositions bulk pumice and glass geochemistry and rhyolite melts modeling
Journal of Petrology, 2013Co-Authors: Ayla S Pamukcu, Tamara L Carley, Calvin F Miller, Guilherme A R Gualda, Charles A FergusonAbstract:The Miocene Peach Spring Tuff is a giant (� 640 km 3 dense rock equivalent) pyroclastic deposit that is extensively exposed in the southwestern USA. Evidence from geochemical and textural analyses of bulk-rocks, glasses, and Accessory Minerals (zircon, titanite, allanite, chevkinite, magnetite) from outflow and intra-caldera pumice clasts and fiamme, in combination with field observations and rhyolite-MELTS modeling, suggests that the Peach Spring magma body was compositionally and thermally zoned with a basal cumulate, and that it crystallized over millennial timescales before being remobilized by mafic input prior to erupting. Crystal contents, bulk compositions, spatial distributions, and temperatures (recorded by Ti in zircon and Zr in titanite) of pumice clasts and fiamme vary systematically: distal outflow high-silica rhyolites are crystal-poor and document lower temperatures; intra-caldera trachytes are crystal-rich and record higher temperatures. These variations indicate that the Peach Spring magma body was zoned. We interpret the outflow high-silica rhyolites to represent the first portion of the magma body to erupt. Zircon and titanite display core-to-edge reductions in rare earth element (REE) concentration and temperature, suggestive of relatively uninterrupted crystallization as the magma body cooled; crystallization temperature intervals from rhyoliteMELTS are consistent with those recorded by zircon and titanite. Exponential size distributions for Accessory Minerals and phenocryst textures are consistent with geochemical evidence for a simple cooling and crystallization history. Intra-caldera trachytes and outflow low-silica rhyolites represent the later portion of the magma body to erupt.This magma experienced a late-stage heating event potentially associated with the onset of the eruption.The edges of titanite crystals are enriched in REE and Zr, and zircon edges are enriched in Ti, suggesting higher temperatures during edge crystallization (at least 9008C). Concave-down crystal size distributions and resorption features on phenocrysts are additional signs of heating. Rare trachyandesite enclaves and the presence of mafic to intermediate lavas immediately underlying the Peach Spring Tuff suggest that a mafic magma input may have been the cause of the heating. Evidence further suggests that the intra-caldera trachytes may represent a remobilized cumulate at the base of the magma body, which retained some melt prior to rejuvenation. Bulk pumice and fiamme compositions are very rich in feldspar and Accessory Mineral phenocrysts, indicative of accumulation of these Minerals; high crystal contents (� 35%) and evidence of heating and resorption imply that this magma was even more crystal-rich prior to the heating event. Rhyolite-MELTS simulations suggest that the trachyte magma had roughly 1wt % water, which cannot be totally accounted for by hydrous phases, thus requiring some amount of melt within the cumulate. Kinked magnetite size distributions are interpreted to represent a change from growth-dominated crystallization (larger crystals, shallow slopes) to nucleation-dominated (small crystals, steep slopes) owing to the onset of eruptive decompression. Timescales of magnetite crystallization calculated from these slopes indicate that the Peach Spring magma body crystallized over millennial timescales, and that eruptive decompression began 10 � 1 ^10 2 years prior to eruption.
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the evolution of the peach spring giant magma body evidence from Accessory Mineral textures and compositions bulk pumice and glass geochemistry and rhyolite melts modeling
Journal of Petrology, 2013Co-Authors: Ayla S Pamukcu, Tamara L Carley, Calvin F Miller, Guilherme A R Gualda, Charles A FergusonAbstract:The Miocene Peach Spring Tuff is a giant (� 640 km 3 dense rock equivalent) pyroclastic deposit that is extensively exposed in the southwestern USA. Evidence from geochemical and textural analyses of bulk-rocks, glasses, and Accessory Minerals (zircon, titanite, allanite, chevkinite, magnetite) from outflow and intra-caldera pumice clasts and fiamme, in combination with field observations and rhyolite-MELTS modeling, suggests that the Peach Spring magma body was compositionally and thermally zoned with a basal cumulate, and that it crystallized over millennial timescales before being remobilized by mafic input prior to erupting. Crystal contents, bulk compositions, spatial distributions, and temperatures (recorded by Ti in zircon and Zr in titanite) of pumice clasts and fiamme vary systematically: distal outflow high-silica rhyolites are crystal-poor and document lower temperatures; intra-caldera trachytes are crystal-rich and record higher temperatures. These variations indicate that the Peach Spring magma body was zoned. We interpret the outflow high-silica rhyolites to represent the first portion of the magma body to erupt. Zircon and titanite display core-to-edge reductions in rare earth element (REE) concentration and temperature, suggestive of relatively uninterrupted crystallization as the magma body cooled; crystallization temperature intervals from rhyoliteMELTS are consistent with those recorded by zircon and titanite. Exponential size distributions for Accessory Minerals and phenocryst textures are consistent with geochemical evidence for a simple cooling and crystallization history. Intra-caldera trachytes and outflow low-silica rhyolites represent the later portion of the magma body to erupt.This magma experienced a late-stage heating event potentially associated with the onset of the eruption.The edges of titanite crystals are enriched in REE and Zr, and zircon edges are enriched in Ti, suggesting higher temperatures during edge crystallization (at least 9008C). Concave-down crystal size distributions and resorption features on phenocrysts are additional signs of heating. Rare trachyandesite enclaves and the presence of mafic to intermediate lavas immediately underlying the Peach Spring Tuff suggest that a mafic magma input may have been the cause of the heating. Evidence further suggests that the intra-caldera trachytes may represent a remobilized cumulate at the base of the magma body, which retained some melt prior to rejuvenation. Bulk pumice and fiamme compositions are very rich in feldspar and Accessory Mineral phenocrysts, indicative of accumulation of these Minerals; high crystal contents (� 35%) and evidence of heating and resorption imply that this magma was even more crystal-rich prior to the heating event. Rhyolite-MELTS simulations suggest that the trachyte magma had roughly 1wt % water, which cannot be totally accounted for by hydrous phases, thus requiring some amount of melt within the cumulate. Kinked magnetite size distributions are interpreted to represent a change from growth-dominated crystallization (larger crystals, shallow slopes) to nucleation-dominated (small crystals, steep slopes) owing to the onset of eruptive decompression. Timescales of magnetite crystallization calculated from these slopes indicate that the Peach Spring magma body crystallized over millennial timescales, and that eruptive decompression began 10 � 1 ^10 2 years prior to eruption.
David Chew - One of the best experts on this subject based on the ideXlab platform.
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sourcing the sand Accessory Mineral fertility analytical and other biases in detrital u pb provenance analysis
Earth-Science Reviews, 2020Co-Authors: David Chew, Gary Osullivan, Luca Caracciolo, Chris Mark, Shane TyrrellAbstract:Abstract Interpreting the wealth of new data derived from the diverse suite of modern single-grain provenance approaches available to a sedimentologist requires a thorough understanding of the potential biases in the information recorded by each Mineral-provenance system. This review focuses on the various possible Mineral-specific biases in U-Pb Accessory Mineral provenance studies employing the Minerals zircon, rutile, apatite, monazite and titanite, focussing on biases resulting from variations in source-rock Mineralogy (fertility). Fertility is intimately linked to the Mineral petrogenesis of crystalline basement sources, which is another key aspect of this review. This petrogenetic information, which often resides in the specialist petrology literature, has great relevance to fertility studies (particularly those measuring Mineral content in modern river sediment using confluence and along-trunk sampling) as trace-element abundances and/or elemental ratios in many Accessory Minerals can be linked to specific lithologies. Other Mineral-specific biases in single-grain provenance analysis considered include physical and chemical modifications both before and after deposition, while the diverse suite of modern single-grain analytical approaches also requires understanding of potential methodological and laboratory induced-biases. A series of multi-proxy provenance studies are presented where fertility bias apparently plays a significant role. In magma-poor metamorphic belts (e.g. segments of the Himalayas and Caledonides-Appalachians), it is shown that zircon growth is limited, and monazite, apatite or rutile associated with the youngest tectonomagmatic events are significantly more fertile. Such multi-proxy provenance studies will be greatly aided in the future by high-throughput, coupled U-Pb age – trace-element analyses integrated with automated heavy Mineral determinations employing highly efficient sample preparation protocols.
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geochronology and thermochronology using apatite time and temperature lower crust to surface
Elements, 2015Co-Authors: David Chew, Richard Alan SpikingsAbstract:Apatite can provide geologists with an exceptionally wide range of ages and temperatures to investigate processes that operate from Earth's surface right down to the lower crust. Apatite is a widespread Accessory Mineral in igneous, metamorphic, and clastic sedimentary rocks and can be dated using four radioactive decay schemes, each with a different temperature window for isotopic closure: Lu–Hf (675–750 °C); U–Pb (350–550 °C); apatite fission track (60–110 °C); (U–Th)/He (40–80 °C). The fission-track and (U–Th)/He methods are popular for studying upper-crustal and near-surface processes, whereas the U–Pb and Lu–Hf systems are used to investigate the thermal, tectonic, and magmatic histories of the deeper crust.
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sr and nd isotopic compositions of apatite reference materials used in u th pb geochronology
Chemical Geology, 2014Co-Authors: Yueheng Yang, David Chew, Jinhui Yang, Liewen Xie, Zhuyin Chu, Yanbin Zhang, Chao HuangAbstract:Abstract Apatite is an important common U- and Th-bearing Accessory Mineral in igneous, metamorphic and clastic sedimentary rocks. The advent of in situ U–Th–Pb apatite geochronology by the SIMS and LA-(MC)-ICP-MS methods has demonstrated the importance of having uniform and homogeneous reference materials. Recently, it has been shown that Sr and Nd isotopic data combined with U–Pb age and trace element concentration data can provide important constraints on apatite paragenesis because this phase usually exhibits high Sr and REE concentrations but has low Rb/Sr ratios which result in negligible corrections for the ingrowth of radiogenic Sr. However, as apatite can potentially have complex internal structures resulting from multiple thermal events, such as inherited cores and metamorphic overgrowths, requires that the Sr and Nd isotopic data should be measured with high spatial resolution. However isobaric interferences hamper the precise determination of Sr or Nd isotopic compositions in LA-MC-ICP-MS analysis. In this work we undertook in situ measurements of Sr and Nd isotopic compositions of eleven apatite reference materials (AP1, AP2, Durango, MAD, Otter Lake, NW-1, Slyudyanka, UWA-1, Mud Tank, McClure Mountain and SDG) commonly used in U–Th–Pb geochronology. Our obtained Sr and Sm–Nd isotopic compositions for these apatite samples are consistent with those values obtained by solution-based methods (isotope dilution and ion chromatography) using MC-ICP-MS or TIMS, which demonstrates the reliability and robustness of our analytical protocol.
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u pb la icpms dating using Accessory Mineral standards with variable common pb
Chemical Geology, 2014Co-Authors: David Chew, Joseph A Petrus, Balz S KamberAbstract:Precise and accurate U-Pb LA-ICPMS dating of many U-bearing Accessory Minerals (e.g. apatite, allanite, titanite and rutile) is often compromised by common Pb. LA-ICPMS dating of these U-bearing Accessory phases typically requires a matrix-matched standard, and data reduction is often complicated by variable incorporation of common Pb not only into the unknowns but also particularly into the reference material. We present here a general approach to common Pb correction in U-Pb LA-ICP-MS dating using a modified version of the VizualAge U-Pb data reduction package for Iolite (VizualAge_UcomPbine). The key feature of the method is that it can correct for variable amounts of common Pb in any U-Pb Accessory Mineral standard as long as the standard is concordant in the U/Pb (and Th/Pb) systems following common Pb correction. Common Pb correction of the age standard can be undertaken using either the Pb-204, Pb-207 or Pb-208((no Th)) methods, and the approach can be applied to raw data files from all widely used modern multi-collector and single-collector ICPMS instruments. VizualAge_UcomPbine first applies a common Pb correction to the user-selected age standard integrations and then fits session-wide "model" U-Pb fractionation curves to the time-resolved U-Pb standard data. This downhole fractionation model is applied to the unknowns and sample-standard bracketing (using a user-specified interpolation method) is used to calculate final isotopic ratios and ages. Pb-204- and Pb-208((no) (Th)) corrected concordia diagrams and Pb-204-, Pb-207- and Pb-208((no Th))-corrected age channels can be calculated for user-specified initial Pb ratio(s). All other conventional common Pb correction methods (e.g. intercept or isochron methods on co-genetic analyses) can be performed offline. The approach was tested on apatite and titanite age standards (for which there are independent constraints on the U-Pb crystallization age) using a Thermo Scientific iCAP-Qc (Q-ICP-MS) coupled to a Photon Machines Analyte Excite 193 nm ArF Excimer laser. Madagascar apatite, OLT1 titanite and R10 rutile were used as primary standards and were corrected for variable common Pb using the new VizualAge_UcomPbine DRS. The secondary Durango (31.44 +/- 0.18 Ma) apatite standard yielded a U-Pb TW concordia intercept age of 31.97 +/- 0.59 Ma (MSWD = 1.09; primary standard corrected by the Pb-207-method) and a U-Pb concordia age of 31.82 +/- 0.40 Ma (MSWD = 1.4; primary standard corrected by the Pb-204-method). McClure Mountain (523.51 +/- 1.47 Ma) yielded a U-Pb TW concordia intercept age of 524.5 +/- 3.7 Ma (MSWD = 0.72) while the Fish Canyon Tuff (28.201 +/- 0.046 Ma) and Khan (522.2 +/- 2.2 Ma) titanite standards yielded U-Pb TW concordia intercept ages of 28.78 +/- 0.41 Ma (MSWD = 1.4) and 520.9 +/- 3.9 Ma (MSWD = 4.2) respectively. The suitability of the Pb-208((no Th))-correction is demonstrated by the agreement between a U-Pb TW concordia intercept age of 452.6 +/- 4.7 Ma (MSWD = 0.89) and a Pb-208((no Th))-corrected TW concordia age of 448.6 +/- 4.5 Ma (MSWD = 1.4) on a c. 450 Ma rutile which exhibits variable incorporation of common Pb. A range of LA-ICPMS U-Pb dating applications are presented and include U-Pb dating of apatite from >3.8 Ga gneisses from Akilia, SW Greenland. These apatites host C-13-depleted graphite inclusions that are interpreted as biogenic in origin and representing the oldest indications of life on Earth. The U-Pb age profiles on single apatite grains presented here are characteristic of Pb loss by volume diffusion with core-rim age differences of up to 300 Ma. These data explain the scatter and poor precision of earlier U-Pb apatite age determinations on Akilia apatite. Other LA-ICPMS dating applications include U-Pb apatite dating as a rapid method for determining the age of mafic intrusions, U-Pb titanite and apatite dating of ash fall tuffs, determining temperature-time histories using multiple U-Pb thermochronometers and improving concordance in LA-ICPMS primary zircon standard datasets by analysing young, common Pb-bearing primary zircon standards that have not accumulated significant radiation damage. (C) 2013 Elsevier B.V. All rights reserved.
Daniela Rubatto - One of the best experts on this subject based on the ideXlab platform.
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the behaviour of monazite from greenschist facies phyllites to anatectic gneisses an example from the chugach metamorphic complex southern alaska
Lithos, 2012Co-Authors: Deta Gasser, Daniela Rubatto, Emilie Bruand, Kurt StuweAbstract:Monazite is a common Accessory Mineral in various metamorphic and magmatic rocks, and is widely used for U–Pb geochronology. However, linking monazite U–Pb ages with the PT evolution of the rock is not always straightforward. We investigated the behaviour of monazite in a metasedimentary sequence ranging from greenschist facies phyllites into upper amphibolites facies anatectic gneisses, which is exposed in the Eocene Chugach Metamorphic Complex of southern Alaska. We investigated textures, chemical compositions and U–Pb dates of monazite grains in samples of differing bulk rock composition and metamorphic grade, with particular focus on the relationship between monazite and other REE-bearing Minerals such as allanite and xenotime. In the greenschist facies phyllites, detrital and metamorphic allanite is present, whereas monazite is absent. In lower amphibolites facies schists (~ 550–650 °C and ≥ 3.4 kbar), small, medium-Y monazite is wide-spread (Mnz1), indicating monazite growth prior and/or simultaneous with growth of garnet and andalusite. In anatectic gneisses, new low-Y, high-Th monazite (Mnz2) crystallised from partial melts, and a third, high-Y, low-Th monazite generation (Mnz3) formed during initial cooling and garnet resorption. U–Pb SHRIMP analysis of the second and third monazite generations yields ages of ~ 55–50 Ma. Monazite became unstable and was overgrown by allanite and/or allanite/epidote/apatite coronas within retrograde muscovite- and/or chlorite-bearing shear zones. This study documents polyphase, complex monazite growth and dissolution during a single, relatively short-lived metamorphic cycle.
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allanite micro geochronology a la icp ms and shrimp u th pb study
Chemical Geology, 2007Co-Authors: Courtney Gregory, Daniela Rubatto, Jorg Hermann, Ian S. Williams, Charlotte M Allen, T R IrelandAbstract:The Accessory Mineral allanite occurs in a wide range of igneous and metamorphic rocks and contains appreciable amounts of trace elements including the REEs, Sr, Th and U. The high degree of compositional substitution and the variable incorporation of common Pb into the allanite crystal structure, however, have limited its use for U–Th–Pb dating. Procedures have now been developed for the isotopic dating of allanite using Laser Ablation ICP-MS and the Sensitive High Resolution Ion Microprobe (SHRIMP). The accuracy of those procedures has been demonstrated by dating six Phanerozoic allanite samples of known age and with different FeO, REE and Th contents. Both analytical techniques require normalising factors for the measurement of 208Pb/232Th and 206Pb/238U, necessitating the use of external matrix-matched standards. The wide range of Th/U in allanite from single samples makes it possible to use multiple LA-ICP-MS analyses to construct Th–Pb isochrons from which ages can be calculated with a precision of 1.4–5.8% (95% confidence level) at a spatial resolution of 32 × 32 × 20μm. A 207Pb-based correction is used to estimate the fraction of common Pb in individual LA-ICP-MS analyses with a precision of 0.3–2%. Accurate (± 1–3%) and precise (1–2%, 95% confidence level) SHRIMP 208Pb/232Th ages can be measured directly on allanite samples with REE + Th > 0.5 atoms per formula unit, without additional matrix corrections at a spatial resolution of 17 × 21 × 2μm. LA-ICP-MS is an efficient technique for dating melt-precipitated allanite (e.g., from igneous or migmatitic rocks). SHRIMP analysis is preferable for samples that have a relatively small grain size, are isotopically complex or have relatively large common Pb contents (e.g., metamorphic allanite).
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exploring the potential of allanite as a geochronometer of high grade crustal processes
Geochimica et Cosmochimica Acta, 2006Co-Authors: Courtney Gregory, Daniela Rubatto, Joerg HermannAbstract:The REE-rich Accessory Mineral allanite plays a key role in the storage and mobility of geochemically important trace elements (LREE, Th) in magmatic and high-grade rocks. Allanite occurs in a wide range of rock types, but of particular interest is its common presence in mafic, migmatitic and high-pressure rocks. We report on the response of allanite trace element chemistry and its U-Th-Pb isotopic system to magmatism, partial melting and eclogite-facies metamorphism. In situ U, Th–Pb geochronology of allanite has been carried out using SHRIMP ion microprobe in conjunction with LA ICP-MS analysis. We analyse allanite with a variety of FeO and trace element compositions from anatectic rocks, granodioritic to tonalitic plutons and high-pressure mafic rocks. Allanite Th– Pb ages are capable of reliably addressing geochronological problems with a precision of 1–2% and 2–5% (2r) for magmatic and metamorphic rocks, respectively. This study allows preliminary conclusions to be made for the closure temperature of allanite. In the case studies presented, no indication of inheritance has been observed for allanite. The trace element composition of allanite records changes in paragenesis. Allanite HREE content relative to LREE provides an indicator for the co-crystallization of garnet. Where allanite formed in migmatites display a small negative Eu anomaly, eclogitic allanite lacks a Eu anomaly, which is related to crystallization in the absence of plagioclase. In addition, the Sr content in allanite can be used as an indicator of crystallization above the stability field of plagioclase. This study demonstrates that allanite can be correlated to major metamorphic and rock-forming Minerals and therefore the P-T conditions of crystallization.
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laser ablation split stream analysis of the sm nd and u pb isotope compositions of monazite titanite and apatite improvements potential reference materials and application to the archean saglek block gneisses
Chemical Geology, 2020Co-Authors: Christopher M Fisher, John M Hanchar, Matthew S A Horstwood, Yan Luo, Ann M Bauer, Chiranjeeb Sarkar, Jeffrey D Vervoort, Simon Tapster, Graham D PearsonAbstract:Abstract Continued improvements in both ICPMS (inductively-coupled plasma mass spectrometry) and laser ablation technologies are fueling advancements in Accessory Mineral investigations and their related isotope systems of interest, and are now being applied to a wide range of geological applications. In this contribution we present an updated methodology for laser ablation split-stream (LASS) analysis of the light rare earth element (LREE) enriched Minerals monazite, titanite, and apatite for simultaneous analysis of the U-Th-Pb age (or trace element content) and the Sm-Nd isotope system. The data were collected with the current generation of high-sensitivity ICPMS and laser systems (ThermoFinnigan NeptunePlus MC-ICPMS and Element XR SF-ICPMS- coupled to a RESOlution 193 nm ArF excimer laser system). The increased sensitivity of these ICPMS instruments allows for improved spatial resolution and the ability to target Minerals which previously contained insufficient concentrations of elements of interest (e.g., Sm-Nd in apatite), making their analysis difficult, if not impossible, using less sensitive instruments. Furthermore, the higher sensitivity allows less aggressive ablation parameters that facilitate thin section sampling and reduces inter-element and isotopic fractionation. To assess and improve the accuracy, precision, and efficiency of the technique, three new potential LASS reference materials (RMs) are evaluated for dual U-Pb and Sm-Nd analysis (Tory Hill apatite, Tory Hill titanite, and Steenskralkamp monazite). The homogeneity of these materials was first assessed using reconnaissance laser ablation analyses, with final characterization of U-Pb age and Sm-Nd isotope composition using isotope-dilution thermal ionization mass spectrometry (ID-TIMS). The precision and accuracy of the LASS method is explored using secondary Mineral reference materials of known age and Sm-Nd isotope composition. The utility of the technique is evaluated with a case study of monazite and apatite from the Eoarchean Uivak Gneiss complex of Labrador, Canada. Finally, we suggest that there is a wide variety of geological applications for this methodology, such as multi-Mineral detrital provenance, crustal growth, and petrogenic studies.