Download or read book Age Composition and Thermal History of Lower Crustal Xenoliths from Artemisia Ekati and Munn Lake Kimberlites of the Slave Craton written by Shauna Marie Coombs and published by . This book was released on 2015 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this study we present data from three lower crustal xenoliths suites collected in a northeast to southwest transect across the Slave craton. The samples are from the Artemisia kimberlite, located near the Coronation diamond district of the northwestern Slave (Nunavut), the Ekati kimberlite from the central Slave (NWT) and the Munn Lake kimberlite of the southeastern Slave (NWT). Samples from the Artemisia Suite have a range of bulk composition but the majority are granitic to semi-pelitic in composition and comprise Garnet + Plagioclase + Quartz + Rutile ± K-feldspar ± Biotite and significant amounts of retrograde hydrous minerals that likely pseudomorph orthopyroxene. As well, there are accessory grains of zircon and monazite. The garnet in these samples is characterized by relatively low grossular contents. In contrast to the Artemisia xenoliths, the Ekati and Munn Lake samples are garnet-bearing mafic granulites with a primary mineralogy of Garnet + Clinopyroxene + Plagioclase ±Quartz ± Orthopyroxene ± Amphibole ± Rutile ± Ilmenite. Metamorphic conditions of the lower crust as indicated by mineral equilibria are in the 9-12 kbar range of pressures with temperatures of at least 750-800°C. In the northern Slave, Neoarchean metamorphic events are recorded at 2624±11 Ma and 2520 Ma and Paleoproterozoic metamorphic events are recorded at 2415 Ma, 2150 Ma, and 2050 Ma and weakly at 2010 Ma. The ages observed in the Artemisia suite may be showing events not seen on the surface and there is a possible correlation with rocks of the Hottah terrane or mafic dike swarms that affected the Slave craton between 2200 and 2000 Ma. Still younger Paleoproterozoic ages of 1826-1868 Ma may be related to the Wopmay orogen. The Artemisia, Ekati and Munn Lake xenolith suites investigated in this study illustrates the complexity of unravelling the history of the lower crust.

Download or read book LA ICP MS Zircon Geochronology of Granulite Xenoliths from the Geronimo Volcanic Field SE Arizona written by Mikaela Alaine Rader and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Characterisation of Mafic Crustal Xenoliths from the Wyoming Craton Montana USA Using Accessory Mineral Geochronology and Geochemistry with Implications for Lower Crustal Evolution written by Yashirvad Thakurdin and published by . This book was released on 2019 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: