U-Pb Zircon Geochronology, Hf Isotope and Trace Element Geochemistry of a Unique Lower Crustal - Upper Mantle Section of a Dying Slow-spreading Mid-ocean Ridge (Macquarie Island, Southern Ocean) PDF Download
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Author: Charles Ryan Jeffcoat
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 96
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Book Description
Author: Charles Ryan Jeffcoat
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 96
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Book Description
Author: Charles Ryan Jeffcoat
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: John M. Hanchar
Publisher: Walter de Gruyter GmbH & Co KG
ISBN: 1501509322
Category : Science
Languages : en
Pages : 520
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Book Description
Volume 53 of Reviews in Mineralogy and Geochemistry covers the most important aspects of zircon-related research over the past twenty-years and highlight possible future research avenues. The chapters review the structure of zircon and other mineral (and synthetic) phases with the zircon structure; the minor and trace element compositions of igneous, metamorphic and hydrothermal zircons; the study of melt inclusions in zircon; experimental and natural studies of zircon saturation and the use of zircon saturation thermometry for natural rocks; cation diffusion and oxygen diffusion in zircon; the historical development of zircon geochronology from the mid-1950s to the present; ID-TIMS, SIMS and ICP-MS; the application of zircon chronology in constraining sediment provenance and the calibration ofthe geologic time-scale; other isotopic systematics; the spectroscopy of zircon, both crystalline and metamict and an atlas of internal textures of zircon.
Author: Melissa Chambers
Publisher:
ISBN:
Category :
Languages : en
Pages : 474
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Author: Marvin A. Lanphere
Publisher:
ISBN:
Category : Cosmochronology
Languages : en
Pages : 404
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Author: M.J. Flowerdew
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Duane C. Petts
Publisher:
ISBN:
Category :
Languages : en
Pages : 370
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Book Description
Zircon from lower crustal xenoliths can preserve unique crustal formation records of unexplored levels of the lithosphere. The first such records for the western Churchill province (Nunavut, Canada) are presented here. Zircon SIMS U-Pb geochronology and oxygen isotope analysis were conducted on kimberlite-hosted granulite-facies xenoliths: four metabasites (⚈ ⚉ ⚊ #9870) from the Rankin Inlet region, and five metabasites (➲ ➳ ➷ ➹ #10179) and three metatonalite/anorthosites (➮ ➴ #10168) from the Repulse Bay region. For the Rankin Inlet suite, oscillatory planar zoned, igneous cores from metabasite xenolith #9865 record dates between ca. 2.9-2.6 Ga, whereas complex to radial-sector zoned metamorphic cores from metabasite xenolith #9864 yield dates between ca. 2.0-1.9 Ga. Oscillatory planar zoned igneous cores from the Repulse Bay suite yield dates of ca. 3.50 and ca. 3.0-2.6 Ga (➮ ➴ #10168). Metamorphic rims from all 12 xenoliths yield dates between ca. 1.75-1.70 Ga, which likely represent regional thermal reworking of the lower crust initiated by magma underplating along the crust-mantle boundary. Irregular, vein-like micro-structures and evidence for solid-state recrystallization are commonly observed using cathodoluminescence within the igneous and metamorphic cores, and likely represent zones affected by intracrystalline Pb-loss and/or Pbredistribution during high-grade metamorphism. The oxygen isotope results for zircon from four metabasites from the Rankin Inlet suite have!18Ozrc values between +5.7 and +8.60 Three metatonalite/anorthosites and five metabasites from the Repulse Bay suite have!18Ozrc values ranging from +5.6 to +8.30 The high!18O values of the oldest igneous cores from xenoliths #10158 and #10164 indicate protolith formation from evolved, supracrustal-derived (i.e., previous contact with surface fluids) tonalite/anorthosite magmas. By comparison, the near-mantle!18O values of igneous cores from metabasite xenolith #9865 and metatonalite/anorthosite xenolith #10168 suggest protolith formation from juvenile magmas. The mantle-like!18O values of ca. 2.0-1.9 Ga metamorphic cores from xenolith #9864 indicate localized reworking of the lower crust caused by regional-scale plate convergence. The wide range of!18O values for all ca. 1.75-1.70 Ga metamorphic rims indicates regional transient heating and reworking of juvenile and evolved, supracrustal-derived lower crust induced by ca. 1.75 Ga magma underplating.
Author: Gillian R. Foulger
Publisher: Geological Society of America
ISBN: 0813724309
Category : Science
Languages : en
Pages : 1012
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Presents a collection of papers discussing various hypotheses and models of planetary plumes.
Author: Mikaela Alaine Rader
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Lower crustal granulite xenoliths entrained in alkaline basalts from the Geronimo Volcanic Field (GVF), SE Arizona, provide constraints on composition, structure, and age of the lower crust in the southern Basin and Range. The GVF is located in the Mazatzal Province, accreted to the southern margin of Laurentia at ~1.69-1.65 Ga. Previous work conducted in this area provided information on the petrology, geochemistry and geothermometry for the xenolith suite, but age constraints of the xenoliths were limited to Nd model ages, making it difficult to place the evolution of the lower crust in the broader context of the geologic history of the region. This project uses zircon U-Pb geochronology and Hf-isotope analysis to determine the age of formation of GVF lower crust, as well as provide evidence for subsequent tectonic events that impacted its composition. Samples for this suite range in composition from mafic meta-cumulates (plg + cpx ± opx ± ol ± sp) to metadiorites and quartzofeldspathic lithologies (plg + kspar + cpx + ox ± qtz ± opx). GVF xenoliths analyzed for U-Pb geochronology present three distinct zircon age populations at ~1.63-1.65 Ga, ~1.48-1.42 Ga, and ~76-2 Ma, with the majority of young ages concentrated between 35-25 Ma. Zircon U-Pb ages for quartzofeldspathic lithologies present evidence of an event at ~1.65 Ga, suggesting an age of formation consistent with the age of the Mazatzal terrane. However, one quartzofeldspathic zircon core was dated at 2.38 Ga, suggesting the presence of an older component during formation of the Mazatzal crust, possibly originating as cratonic Laurentian sediment. Two quartzofeldspathic xenoliths (MR-GN21-39 and MR-GN21-53) contain zircon cores with discordant U-Pb ages that trend toward ~1.48-1.42 Ga, suggesting modification of the Mazatzal terrane beginning at ~1.48 Ga, the onset of the Picuris Orogeny and widespread 1.48-1.35 Ga plutonism in the southwestern US. These same quartzofeldspathic samples present young ages ranging from ~50-15 Ma, suggesting later alteration of the Proterozoic terrane by Tertiary magmatism associated with Farallon slab subduction. Metadiorites, which were previously inferred to be ~ 1.4 Ga on the basis of whole rock Nd model ages, yielded zircon U-Pb ages ranging from ~76 to 2 Ma, suggesting an origin through thermal resetting of zircons in older Paleoproterozoic crust or addition of new juvenile melts that assimilated Paleoproterozoic crust during magmatic underplating in the Cenozoic. Zircon Hf isotope data from both quartzofeldspathic and metadiorite lithologies are consistent with mantle separation at 2.4 Ga, following an intermediate (176Lu/177Hf = 0.018) crustal isotope evolution path. The existence of positive [epsilon]Hf(t) values in Mesoproterozoic zircon cores of some quartzofeldspathic xenoliths suggest reworking of this older Paleoproterozoic crust sometime between the time of Mazatzal formation and the 1.4 Ga Picuris orogeny and/or the widespread A-type granite event that also occurred across Laurentia at about this time. Eocene to Oligocene age zircons have [epsilon]Hf(t) values that range from -17 to 0, suggesting significant lower crustal modification during Farallon slab subduction.
Author: Stanton B. Ingram
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 89
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Book Description
The Alabama eastern Blue Ridge (EBR) of the Southern Appalachian Mountains hosts a variety of felsic plutonic rocks, which intrude multiply deformed Neoproterozoic to Ordovician metasedimentary rocks. Plutons consist of two distinct suites based on geochemical composition and degree of deformation: pre- to syn-kinematic Neoacadian, low Sr/Y plutons (ca. 380-360 Ma) and late- to post-kinematic, Early Alleghanian high Sr/Y plutons (ca. 350-330 Ma). Here, I report new whole rock geochemistry, U-Pb zircon SHRIMP-RG (Sensitive High Resolution Ion Micro Probe-Reverse Geometry) ages, and Hf isotope data for 6 plutons in the Alabama EBR. Low Sr/Y plutons are predominantly biotite-muscovite granites and granodiorites and include the Rockford Granite (376.6 ± 1.5 Ma) and the Bluff Springs Granite (363.8 ± 2.9 Ma). The Enitachopco trondhjemite dike also displays a Neoacadian age of 366.5 ± 3.5 Ma. Zircon Hf isotope data from the low Sr/Y suite range from -11.2 to +2.0. These plutons are in general strongly deformed, and display geochemical characteristics consistent with mid crustal (
