Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges
To explore the ability of melting mafic lithologies to produce alkaline ocean-island basalts (OIB), a study was carried out measuring clinopyroxene (Cpx)- melt and garnet (Gt)-melt partition coefficients during silica-poor garnet pyroxenite melting for a suite of trace elements, including U and Th,...
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ftdtic:ADA501860 2023-05-15T14:54:24+02:00 Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges Elkins, Lynne J. MASSACHUSETTS INST OF TECH CAMBRIDGE CENTER FOR METEOROLOGY AND PHYSICAL OCEANOGRAPHY 2009-02 text/html http://www.dtic.mil/docs/citations/ADA501860 http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA501860 en eng http://www.dtic.mil/docs/citations/ADA501860 Approved for public release; distribution is unlimited. DTIC Physical and Dynamic Oceanography Geology Geochemistry and Mineralogy *RADIOACTIVE ISOTOPES *GEOLOGIC AGE DETERMINATION *OCEAN RIDGES MELTING NEODYMIUM STRONTIUM URANIUM GARNET TRACE ELEMENTS LEAD(METAL) THORIUM ARCTIC OCEAN ISLANDS GEOLOGIC MODELS MARINE GEOLOGY MAGMA THESES BASALT CLINOPYROXENE GARNET PYROXENITE KOLBEINSEY RIDGE MAGMA TRANSPORT PROCESSES Text 2009 ftdtic 2016-02-22T20:31:12Z To explore the ability of melting mafic lithologies to produce alkaline ocean-island basalts (OIB), a study was carried out measuring clinopyroxene (Cpx)- melt and garnet (Gt)-melt partition coefficients during silica-poor garnet pyroxenite melting for a suite of trace elements, including U and Th, at 2.5GPa and 1420-1450 degrees C. Forward-melting calculations using the results to model time-dependent uranium-series isotopes do not support presence of a fixed quantity of garnet pyroxenite in the source of OIB. To use U-series isotopes to further constrain mantle heterogeneity and the timing and nature of melting and melt transport processes, U-Th-Pa-Ra disequilibria, radiogenic isotopes, and trace-element compositions were measured for the slow-spreading Arctic mid-ocean ridges (MOR). A case study of 33 young MOR basalts (MORB) from the shallow endmember of the global ridge system, the Kolbeinsey Ridge found that unaltered Kolbeinsey MORB have universally high (230Th/238U) (1.165-1.296) and relatively uniform (230Th/232Th) (1.196-1.324), SigmaNd, 87Sr/86Sr SigmaHf, and Pb isotopes. This suggests a homogeneous mantle source and a long peridotite melting column produces the thick Kolbeinsey crust. Trace element ratios suggest a young, depleted mantle source. Data from the slow- to ultraslow Mohns and Knipovich Ridges north of Kolbeinsey form a sloped array, and (230Th/232Th) correlates systematically with radiogenic isotopic variations. These data are readily reproduced by models for heterogeneous mantle melting. MORB from 85 degrees E on the global ultraslow-spreading endmember Gakkel Ridge are homogeneously depleted with low (230Th/238U) and high (226Ra/230Th) that lie along a global negative correlation. Arctic data support a global mantle temperature control on mean (230Th/238U). Sponsored in part by the the National Defense Science and Engineering Graduate Fellowship Program. The original document contains color images. Text Arctic Arctic Ocean Kolbeinsey Ocean Island Defense Technical Information Center: DTIC Technical Reports database Arctic Arctic Ocean Gakkel Ridge ENVELOPE(90.000,90.000,87.000,87.000) Kolbeinsey ENVELOPE(-18.687,-18.687,67.149,67.149) Kolbeinsey Ridge ENVELOPE(-16.917,-16.917,68.833,68.833) |
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Open Polar |
collection |
Defense Technical Information Center: DTIC Technical Reports database |
op_collection_id |
ftdtic |
language |
English |
topic |
Physical and Dynamic Oceanography Geology Geochemistry and Mineralogy *RADIOACTIVE ISOTOPES *GEOLOGIC AGE DETERMINATION *OCEAN RIDGES MELTING NEODYMIUM STRONTIUM URANIUM GARNET TRACE ELEMENTS LEAD(METAL) THORIUM ARCTIC OCEAN ISLANDS GEOLOGIC MODELS MARINE GEOLOGY MAGMA THESES BASALT CLINOPYROXENE GARNET PYROXENITE KOLBEINSEY RIDGE MAGMA TRANSPORT PROCESSES |
spellingShingle |
Physical and Dynamic Oceanography Geology Geochemistry and Mineralogy *RADIOACTIVE ISOTOPES *GEOLOGIC AGE DETERMINATION *OCEAN RIDGES MELTING NEODYMIUM STRONTIUM URANIUM GARNET TRACE ELEMENTS LEAD(METAL) THORIUM ARCTIC OCEAN ISLANDS GEOLOGIC MODELS MARINE GEOLOGY MAGMA THESES BASALT CLINOPYROXENE GARNET PYROXENITE KOLBEINSEY RIDGE MAGMA TRANSPORT PROCESSES Elkins, Lynne J. Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges |
topic_facet |
Physical and Dynamic Oceanography Geology Geochemistry and Mineralogy *RADIOACTIVE ISOTOPES *GEOLOGIC AGE DETERMINATION *OCEAN RIDGES MELTING NEODYMIUM STRONTIUM URANIUM GARNET TRACE ELEMENTS LEAD(METAL) THORIUM ARCTIC OCEAN ISLANDS GEOLOGIC MODELS MARINE GEOLOGY MAGMA THESES BASALT CLINOPYROXENE GARNET PYROXENITE KOLBEINSEY RIDGE MAGMA TRANSPORT PROCESSES |
description |
To explore the ability of melting mafic lithologies to produce alkaline ocean-island basalts (OIB), a study was carried out measuring clinopyroxene (Cpx)- melt and garnet (Gt)-melt partition coefficients during silica-poor garnet pyroxenite melting for a suite of trace elements, including U and Th, at 2.5GPa and 1420-1450 degrees C. Forward-melting calculations using the results to model time-dependent uranium-series isotopes do not support presence of a fixed quantity of garnet pyroxenite in the source of OIB. To use U-series isotopes to further constrain mantle heterogeneity and the timing and nature of melting and melt transport processes, U-Th-Pa-Ra disequilibria, radiogenic isotopes, and trace-element compositions were measured for the slow-spreading Arctic mid-ocean ridges (MOR). A case study of 33 young MOR basalts (MORB) from the shallow endmember of the global ridge system, the Kolbeinsey Ridge found that unaltered Kolbeinsey MORB have universally high (230Th/238U) (1.165-1.296) and relatively uniform (230Th/232Th) (1.196-1.324), SigmaNd, 87Sr/86Sr SigmaHf, and Pb isotopes. This suggests a homogeneous mantle source and a long peridotite melting column produces the thick Kolbeinsey crust. Trace element ratios suggest a young, depleted mantle source. Data from the slow- to ultraslow Mohns and Knipovich Ridges north of Kolbeinsey form a sloped array, and (230Th/232Th) correlates systematically with radiogenic isotopic variations. These data are readily reproduced by models for heterogeneous mantle melting. MORB from 85 degrees E on the global ultraslow-spreading endmember Gakkel Ridge are homogeneously depleted with low (230Th/238U) and high (226Ra/230Th) that lie along a global negative correlation. Arctic data support a global mantle temperature control on mean (230Th/238U). Sponsored in part by the the National Defense Science and Engineering Graduate Fellowship Program. The original document contains color images. |
author2 |
MASSACHUSETTS INST OF TECH CAMBRIDGE CENTER FOR METEOROLOGY AND PHYSICAL OCEANOGRAPHY |
format |
Text |
author |
Elkins, Lynne J. |
author_facet |
Elkins, Lynne J. |
author_sort |
Elkins, Lynne J. |
title |
Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges |
title_short |
Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges |
title_full |
Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges |
title_fullStr |
Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges |
title_full_unstemmed |
Basalt Petrogenesis Beneath Slow - and Ultraslow-Spreading Arctic Mid-Ocean Ridges |
title_sort |
basalt petrogenesis beneath slow - and ultraslow-spreading arctic mid-ocean ridges |
publishDate |
2009 |
url |
http://www.dtic.mil/docs/citations/ADA501860 http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA501860 |
long_lat |
ENVELOPE(90.000,90.000,87.000,87.000) ENVELOPE(-18.687,-18.687,67.149,67.149) ENVELOPE(-16.917,-16.917,68.833,68.833) |
geographic |
Arctic Arctic Ocean Gakkel Ridge Kolbeinsey Kolbeinsey Ridge |
geographic_facet |
Arctic Arctic Ocean Gakkel Ridge Kolbeinsey Kolbeinsey Ridge |
genre |
Arctic Arctic Ocean Kolbeinsey Ocean Island |
genre_facet |
Arctic Arctic Ocean Kolbeinsey Ocean Island |
op_source |
DTIC |
op_relation |
http://www.dtic.mil/docs/citations/ADA501860 |
op_rights |
Approved for public release; distribution is unlimited. |
_version_ |
1766326118166560768 |