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Larry M Heaman - One of the best experts on this subject based on the ideXlab platform.
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duration and periodicity of kimberlite volcanic activity in the lac de gras kimberlite field canada and some recommendations for kimberlite geochronology
2015Co-Authors: Chiranjeeb Sarkar, Larry M Heaman, D G PearsonAbstract:Abstract Establishing the Emplacement ages and distribution pattern of Central Slave kimberlites has played a key role in diamond exploration within the Lac de Gras kimberlite field. Nonetheless, Emplacement age information is lacking for approximately 80% of the known kimberlites in this field making the assessment of Emplacement age patterns difficult. This study expands the number and geographic coverage of kimberlite Emplacement ages within the Lac de Gras field to re-assess the absolute timing, duration, and possible number of pulses of kimberlite eruption. U–Pb perovskite ages for eight previously undated kimberlites and an additional thirteen kimberlites, which were previously dated by either the Rb–Sr or U–Pb methods, fall within the age range of 75–45 Ma, as previously suggested for kimberlite magmatism in this area. We report the first Carboniferous age kimberlite in the Central Lac de Gras field – the Eddie kimberlite – with a U–Pb perovskite age of 321.0 ± 3.0 Ma. A compilation of 57 kimberlite Emplacement ages from the central Lac de Gras field was evaluated using probability density and mixture modeling methods. Five short-duration (4–5 Ma) periods of kimberlite magmatism are recognized at 48, 54, 61, 66 and 72 Ma; the three younger pulses have been previously recognized and remain relatively unchanged. The 54 Ma pulse represents the major kimberlite eruption event containing ~ 40% of the currently dated kimberlites in Lac de Gras field. A detailed evaluation of the temporal–spatial evolution of Lac de Gras kimberlites reveals that the oldest diamond-poor kimberlites (75–60 Ma) were emplaced in the northern and eastern parts of the field whereas the younger (55–48 Ma) economic kimberlites are concentrated in the center of the field.
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precise u pb dating of paleoproterozoic mafic dyke swarms of the dharwar craton india implications for the existence of the neoarchean supercraton sclavia
2010Co-Authors: Jason E French, Larry M HeamanAbstract:Abstract We report seven high precision U–Pb age determinations for mafic dykes from a number of major Precambrian swarms located in the Dharwar craton, south India. These new age results define two previously unrecognized widespread Paleoproterozoic dyking events at 2221–2209 and 2181–2177 Ma, and confirm a third at 2369–2365 Ma. Three parallel E–W trending mafic dykes from the petrographically and geochemically variable Bangalore dyke swarm, the most prominent swarm in the Dharwar craton, yield indistinguishable U–Pb baddeleyite ages of 2365.4 ± 1.0, 2365.9 ± 1.5 and 2368.6 ± 1.3 Ma, indicating rapid Emplacement in less than five million years. A compilation of Paleoproterozoic U–Pb ages for mafic magmatic events worldwide indicates that the 2369–2365 Ma Bangalore dyke swarm represents a previously unrecognized pulse of mafic magmatism on Earth. A protracted episode of Pan-Dharwar mafic dyke swarm Emplacement at ∼2.2 Ga is the most geographically widespread Paleoproterozoic mafic magmatic event currently recognized in the Dharwar craton. U–Pb baddeleyite dating of two dykes located south of the Cuddapah basin yield ages of 2220.5 ± 4.9 Ma (N–S trending Kandlamadugu dyke) and 2209.3 ± 2.8 Ma (NW–SE trending Somala dyke), indicating Emplacement of two distinct subswarms in the region. Two dykes from the northern Dharwar craton (the E–W Bandepalem and NW–SE Dandeli dykes) separated by ∼550 km yield indistinguishable U–Pb ages of 2176.5 ± 3.7 (baddeleyite and zircon) and 2180.8 ± 0.9 Ma (baddeleyite), respectively. Collectively, these age data hint at the presence of a giant 2.18 Ga radiating mafic dyke swarm that spans >100,000 km 2 of the Dharwar craton, which has a focal point west of the present day Deccan Flood basalt province. The identification of Pan-Dharwar mafic dyke swarm Emplacement at ∼2.2 Ga allows for new global correlations with contemporaneous mafic magmatic events previously recognized in many other Archean cratons worldwide (e.g., within Antarctica, Australia, Finland, Greenland, and North America). Increasing evidence suggests that this global mafic magmatism at ∼2.2 Ga was linked with intracontinental rifting, enhanced mantle plume activity, and the breakup of one or more Archean continents. We highlight the similarity in timing of Paleoproterozoic (2.23–2.17 Ga) mafic dyke swarm Emplacement recorded in the Dharwar and Slave cratons and use the correlation of high precision U–Pb ages, geometry and regional patterns of mafic dyke swarm Emplacement, and matching Archean geology in these cratons as reconstruction pins to constrain the configuration of the ∼2.2 Ga supercraton Sclavia.
Erika Ronchin - One of the best experts on this subject based on the ideXlab platform.
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Syn-Emplacement Fracturing in the Sandfell Laccolith, Eastern Iceland—Implications for Rhyolite Intrusion Growth and Volcanic Hazards
2018Co-Authors: Tobias Mattsson, Steffi Burchardt, Bjarne S G Almqvist, Erika RonchinAbstract:Felsic magma commonly pools within shallow mushroom-shaped magmatic intrusions, so-called laccoliths or cryptodomes, which can cause both explosive eruptions and collapse of the volcanic edifice. Deformation during laccolith Emplacement is primarily considered to occur in the host rock. However, shallowly emplaced laccoliths (cryptodomes) show extensive internal deformation. While deformation of magma in volcanic conduits is an important process for regulating eruptive behavior, the effects of magma deformation on intrusion Emplacement remain largely unexplored. In this study, we investigate the Emplacement of the 0.57 km3 rhyolitic Sandfell laccolith, Iceland, which formed at a depth of 500 m in a single intrusive event. By combining field measurements, 3D modeling, anisotropy of magnetic susceptibility (AMS), microstructural analysis, and FEM modeling we examine deformation in the magma to constrain its influence on intrusion Emplacement. Concentric flow bands and S-C fabrics reveal contact-parallel magma flow during the initial stages of laccolith inflation. The magma flow fabric is overprinted by strain-localization bands (SLBs) and more than one third of the volume of the Sandfell laccolith displays concentric intensely fractured layers. A dominantly oblate magmatic fabric in the fractured areas and conjugate geometry of SLBs, and fractures in the fracture layers demonstrate that the magma was deformed by intrusive stresses. This implies that a large volume of magma became viscously stalled and was unable to flow during intrusion. Fine-grained groundmass and vesicle-poor rock adjacent to the fracture layers point to that the interaction between the SLBs and the flow bands at sub-solidus state caused the brittle-failure and triggered decompression degassing and crystallization, which led to rapid viscosity increase in the magma. The extent of syn-Emplacement fracturing in the Sandfell laccolith further shows that strain-induced degassing limited the amount of eruptible magma by essentially solidifying the rim of the magma body. Our observations indicate that syn-Emplacement changes in rheology, and the associated fracturing of intruding magma not only occur in volcanic conduits, but also play a major role in the Emplacement of viscous magma intrusions in the upper kilometer of the crust
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insights into cryptodome Emplacement from the sandfell laccolith eastern iceland implications for seismic and geodetic monitoring
2017Co-Authors: Tobias Mattsson, Steffi Burchardt, Bjarne S G Almqvist, Erika RonchinAbstract:Insights into cryptodome Emplacement from the Sandfell laccolith, eastern Iceland – implications for seismic and geodetic monitoring
Sverre Planke - One of the best experts on this subject based on the ideXlab platform.
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rapid magma Emplacement in the karoo large igneous province
2012Co-Authors: Henrik Svensen, Fernando Corfu, Stephane Polteau, Oyvind Hammer, Sverre PlankeAbstract:Abstract Understanding the dynamics of continental Large Igneous Provinces (LIPs) relies on precise dating of basaltic rocks. LIP research has traditionally focused on dating lavas, often neglecting the volumetrically important sill intrusions in underlying sedimentary basins. Here we present U–Pb zircon (and baddeleyite) ages for fourteen new samples of Karoo LIP sills and dykes spaced by as much as 1100 km across the half million square kilometer Karoo Basin. The samples yield remarkably coherent ages ranging from 183.0 ± 0.5 to 182.3 ± 0.6 myr. Probability modeling indicates that basin scale Emplacement took place within an interval of about 0.47 myrs (less than 0.90 myrs with 95% confidence), and could even have represented a single magma Emplacement event. Combining the new ages with the estimated volume of sills in the Karoo Basin gives an Emplacement rate of 0.78 km3/yr, which is higher than previous estimates. Upper crustal magma storage may account for these high rates. The results challenge the view that melt Emplacement in a sedimentary basin is a prolonged process, support a scenario of pulsating catastrophic events within a narrow time frame, and strengthens the hypothesis linking LIPs and sill Emplacement to global environmental crises.
Josh Stachnik - One of the best experts on this subject based on the ideXlab platform.
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the distribution and composition of high velocity lower crust across the continental u s comparison of seismic and xenolith data and implications for lithospheric dynamics and history
2017Co-Authors: Vera Schultepelkum, K H Mahan, Weisen Shen, Josh StachnikAbstract:The composition of the continental lower crust is not well known. High seismic wavespeeds may indicate mafic or garnet-bearing material, with implications for Emplacement history, evolution, and rheological and dynamic behavior. In this contribution, we use recent seismic results from the EarthScope Transportable Array, compilations of active source studies, and selected xenolith studies to attempt to map the distribution of high-velocity lower crust across the continental U.S. and assess its relationship to proposed Emplacement and destruction-related mechanisms such as under-and intraplating, collision, extension, heating, cooling, hydration, and delamination. Thin layers of high-velocity lower crust related to regional processes are found scattered throughout the continent. Thicker layers in large areas are found in the central and eastern U.S. in areas with thick crust, bounded roughly by the Rocky Mountain Front. Emplacement processes likely originally spanned this boundary, and the difference between the two domains may reflect garnet growth with cooling and aging of continental crust in much of the central and eastern U.S., while crustal thickness and lithospheric temperatures in the western U.S. are unfavorable for growth and maintenance of thick layers of high-velocity garnet-bearing lower crust.
Jason E French - One of the best experts on this subject based on the ideXlab platform.
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precise u pb dating of paleoproterozoic mafic dyke swarms of the dharwar craton india implications for the existence of the neoarchean supercraton sclavia
2010Co-Authors: Jason E French, Larry M HeamanAbstract:Abstract We report seven high precision U–Pb age determinations for mafic dykes from a number of major Precambrian swarms located in the Dharwar craton, south India. These new age results define two previously unrecognized widespread Paleoproterozoic dyking events at 2221–2209 and 2181–2177 Ma, and confirm a third at 2369–2365 Ma. Three parallel E–W trending mafic dykes from the petrographically and geochemically variable Bangalore dyke swarm, the most prominent swarm in the Dharwar craton, yield indistinguishable U–Pb baddeleyite ages of 2365.4 ± 1.0, 2365.9 ± 1.5 and 2368.6 ± 1.3 Ma, indicating rapid Emplacement in less than five million years. A compilation of Paleoproterozoic U–Pb ages for mafic magmatic events worldwide indicates that the 2369–2365 Ma Bangalore dyke swarm represents a previously unrecognized pulse of mafic magmatism on Earth. A protracted episode of Pan-Dharwar mafic dyke swarm Emplacement at ∼2.2 Ga is the most geographically widespread Paleoproterozoic mafic magmatic event currently recognized in the Dharwar craton. U–Pb baddeleyite dating of two dykes located south of the Cuddapah basin yield ages of 2220.5 ± 4.9 Ma (N–S trending Kandlamadugu dyke) and 2209.3 ± 2.8 Ma (NW–SE trending Somala dyke), indicating Emplacement of two distinct subswarms in the region. Two dykes from the northern Dharwar craton (the E–W Bandepalem and NW–SE Dandeli dykes) separated by ∼550 km yield indistinguishable U–Pb ages of 2176.5 ± 3.7 (baddeleyite and zircon) and 2180.8 ± 0.9 Ma (baddeleyite), respectively. Collectively, these age data hint at the presence of a giant 2.18 Ga radiating mafic dyke swarm that spans >100,000 km 2 of the Dharwar craton, which has a focal point west of the present day Deccan Flood basalt province. The identification of Pan-Dharwar mafic dyke swarm Emplacement at ∼2.2 Ga allows for new global correlations with contemporaneous mafic magmatic events previously recognized in many other Archean cratons worldwide (e.g., within Antarctica, Australia, Finland, Greenland, and North America). Increasing evidence suggests that this global mafic magmatism at ∼2.2 Ga was linked with intracontinental rifting, enhanced mantle plume activity, and the breakup of one or more Archean continents. We highlight the similarity in timing of Paleoproterozoic (2.23–2.17 Ga) mafic dyke swarm Emplacement recorded in the Dharwar and Slave cratons and use the correlation of high precision U–Pb ages, geometry and regional patterns of mafic dyke swarm Emplacement, and matching Archean geology in these cratons as reconstruction pins to constrain the configuration of the ∼2.2 Ga supercraton Sclavia.
