SEG Technical Program Expanded Abstracts 2008, 2008
An extensive physical property database has been compiled from measurements of density and suscep... more An extensive physical property database has been compiled from measurements of density and susceptibility on the Bellevue drillcore from the northern lobe of the Bushveld Complex in South Africa. Analysis of these data was performed using wavelets and statistical tools, including the development of a windowed histogram plot. This study has revealed significant patterns and cycles on various scales that were previously unrecognized in the Bushveld Complex. These cycles correlate both with lithology variations and subtle layering within and between units. A surprise result was the presence of layering in the Main Zone density data at ~170 m intervals, where the densities are increasing upwards in each cycle. The methods developed here are suitable for investigating subtle periodic features in layering that may not be readily apparent in the data.
Proceedings of the National Academy of Sciences of the United States of America, Jan 30, 2015
The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active ... more The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland-and especially the Öræfajökull volcano-is characterized by a unique enriched-mantle component (EM2-like) with elevated (87)Sr/(86)Sr and (207)Pb/(204)Pb. Here, we demonstrate through modeling of Sr-Nd-Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2-6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide...
Mafic dikes and sheets rich in Fe, Ti-oxides and apatite are commonly associated with Proterozoic... more Mafic dikes and sheets rich in Fe, Ti-oxides and apatite are commonly associated with Proterozoic massif anorthosites and are referred to as oxide-apatite gabbronorites (OAGN). Within the Adirondacks, field evidence indicates that during middle to late stages of anorthositic evolution, these bodies were emplaced as magmas with unspecified liquid-crystal ratios. Sixty whole rock analyses of Adirondack OAGN and related rocks
SEG Technical Program Expanded Abstracts 2008, 2008
An extensive physical property database has been compiled from measurements of density and suscep... more An extensive physical property database has been compiled from measurements of density and susceptibility on the Bellevue drillcore from the northern lobe of the Bushveld Complex in South Africa. Analysis of these data was performed using wavelets and statistical tools, including the development of a windowed histogram plot. This study has revealed significant patterns and cycles on various scales that were previously unrecognized in the Bushveld Complex. These cycles correlate both with lithology variations and subtle layering within and between units. A surprise result was the presence of layering in the Main Zone density data at ~170 m intervals, where the densities are increasing upwards in each cycle. The methods developed here are suitable for investigating subtle periodic features in layering that may not be readily apparent in the data.
Proceedings of the National Academy of Sciences of the United States of America, Jan 30, 2015
The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active ... more The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland-and especially the Öræfajökull volcano-is characterized by a unique enriched-mantle component (EM2-like) with elevated (87)Sr/(86)Sr and (207)Pb/(204)Pb. Here, we demonstrate through modeling of Sr-Nd-Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2-6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide...
Mafic dikes and sheets rich in Fe, Ti-oxides and apatite are commonly associated with Proterozoic... more Mafic dikes and sheets rich in Fe, Ti-oxides and apatite are commonly associated with Proterozoic massif anorthosites and are referred to as oxide-apatite gabbronorites (OAGN). Within the Adirondacks, field evidence indicates that during middle to late stages of anorthositic evolution, these bodies were emplaced as magmas with unspecified liquid-crystal ratios. Sixty whole rock analyses of Adirondack OAGN and related rocks
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Papers by Lewis Ashwal