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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Africa
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Southern Africa
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South Africa
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Free State South Africa
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Vredefort Dome (1)
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Witwatersrand (1)
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Asia
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Far East
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Japan (1)
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Laos (1)
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Canada (1)
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Chicxulub Crater (1)
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Europe
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Baltic region
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Estonia (1)
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Central Europe
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Germany
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Bavaria Germany
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Ries Crater (1)
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Southern Europe
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Italy
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Umbria Italy
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Perugia Italy
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Gubbio Italy (1)
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Western Europe
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Scandinavia
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Sweden
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Dalarna Sweden
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Siljan (1)
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Siljan Ring (1)
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Jamtland Sweden
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Lockne Crater (1)
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United Kingdom
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Great Britain
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Scotland
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Perthshire Scotland (1)
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Mexico
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Yucatan Mexico (1)
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-
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commodities
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glass materials (2)
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elements, isotopes
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isotope ratios (2)
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isotopes
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radioactive isotopes
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Ar-38 (1)
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stable isotopes
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He-3 (1)
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Ne-21 (1)
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O-17/O-16 (1)
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O-18/O-16 (1)
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Pb-207/Pb-206 (1)
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metals
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alkaline earth metals
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calcium (1)
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chromium (1)
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iron
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ferric iron (1)
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lead
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Pb-207/Pb-206 (1)
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nickel (3)
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rare earths (1)
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noble gases
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argon
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Ar-38 (1)
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helium
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He-3 (1)
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neon
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Ne-21 (1)
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oxygen
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O-17/O-16 (1)
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O-18/O-16 (1)
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silicon (1)
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geochronology methods
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(U-Th)/He (1)
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Ar/Ar (1)
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exposure age (1)
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K/Ar (1)
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U/Pb (2)
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geologic age
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Cenozoic
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Tertiary
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Paleogene
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Paleocene
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lower Paleocene
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K-T boundary (1)
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Mesozoic
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Cretaceous
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Upper Cretaceous
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K-T boundary (1)
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Turonian (1)
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Paleozoic
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Devonian
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Upper Devonian (1)
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Ordovician
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Middle Ordovician (1)
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Upper Ordovician (1)
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Phanerozoic (1)
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Precambrian
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Archean (1)
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metamorphic rocks
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metamorphic rocks
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impactites (1)
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meteorites
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meteorites
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Dhofar Meteorites (1)
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iron meteorites
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octahedrite
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Sikhote-Alin Meteorite (1)
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micrometeorites (2)
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stony meteorites
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achondrites
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Martian meteorites
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SNC Meteorites
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shergottite
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Zagami Meteorite (1)
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chondrites
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carbonaceous chondrites
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CB chondrites (1)
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ordinary chondrites
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H chondrites (2)
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L chondrites
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Tsarev Meteorite (1)
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LL chondrites (1)
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minerals
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alloys
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kamacite (3)
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phosphides
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schreibersite (1)
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taenite (4)
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native elements
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diamond (1)
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oxides
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chrome spinel (1)
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chromite (2)
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ferropericlase (1)
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hollandite (3)
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ilmenite (2)
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iron oxides (1)
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spinel (2)
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spinel group (1)
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phosphates
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apatite (1)
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merrillite (1)
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whitlockite (2)
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silicates
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aluminosilicates
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maskelynite (5)
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chain silicates
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pyroxene group
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clinopyroxene
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diopside (1)
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hedenbergite (1)
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jadeite (5)
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orthopyroxene (1)
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framework silicates
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feldspar group
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plagioclase
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albite (2)
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silica minerals
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cristobalite (1)
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quartz (2)
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stishovite (1)
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orthosilicates
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nesosilicates
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garnet group
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majorite (9)
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pyrope (3)
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olivine group
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olivine (9)
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ringwoodite (10)
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wadsleyite (4)
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sulfides
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chalcopyrite (1)
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pyrrhotite (1)
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troilite (3)
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Primary terms
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absolute age (2)
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Africa
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Southern Africa
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South Africa
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Free State South Africa
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Vredefort Dome (1)
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Witwatersrand (1)
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Asia
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Far East
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Japan (1)
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Laos (1)
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-
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asteroids (5)
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Canada (1)
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Cenozoic
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Tertiary
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Paleogene
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Paleocene
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lower Paleocene
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K-T boundary (1)
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crystal chemistry (3)
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crystal structure (6)
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deformation (1)
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Europe
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Baltic region
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Estonia (1)
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Central Europe
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Germany
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Bavaria Germany
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Ries Crater (1)
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Southern Europe
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Italy
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Umbria Italy
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Perugia Italy
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Gubbio Italy (1)
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-
-
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Western Europe
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Scandinavia
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Sweden
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Dalarna Sweden
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Siljan (1)
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Siljan Ring (1)
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Jamtland Sweden
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Lockne Crater (1)
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United Kingdom
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Great Britain
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Scotland
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Perthshire Scotland (1)
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-
-
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geochemistry (4)
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inclusions (1)
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isotopes
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radioactive isotopes
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Ar-38 (1)
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stable isotopes
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He-3 (1)
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Ne-21 (1)
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O-17/O-16 (1)
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O-18/O-16 (1)
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Pb-207/Pb-206 (1)
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Mesozoic
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Cretaceous
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Upper Cretaceous
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K-T boundary (1)
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Turonian (1)
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-
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metals
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alkaline earth metals
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calcium (1)
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chromium (1)
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iron
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ferric iron (1)
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lead
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Pb-207/Pb-206 (1)
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nickel (3)
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rare earths (1)
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metamorphic rocks
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impactites (1)
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metamorphism (18)
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meteorites
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Dhofar Meteorites (1)
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iron meteorites
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octahedrite
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Sikhote-Alin Meteorite (1)
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-
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micrometeorites (2)
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stony meteorites
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achondrites
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Martian meteorites
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SNC Meteorites
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shergottite
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Zagami Meteorite (1)
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chondrites
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carbonaceous chondrites
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CB chondrites (1)
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ordinary chondrites
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H chondrites (2)
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L chondrites
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Tsarev Meteorite (1)
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LL chondrites (1)
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Mexico
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Yucatan Mexico (1)
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Moon (2)
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noble gases
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argon
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Ar-38 (1)
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helium
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He-3 (1)
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neon
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Ne-21 (1)
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-
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oxygen
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O-17/O-16 (1)
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O-18/O-16 (1)
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Paleozoic
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Devonian
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Upper Devonian (1)
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Ordovician
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Middle Ordovician (1)
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Upper Ordovician (1)
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petrology (2)
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Phanerozoic (1)
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phase equilibria (1)
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Precambrian
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Archean (1)
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sea water (1)
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sedimentary rocks
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chemically precipitated rocks
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ironstone (1)
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clastic rocks
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black shale (1)
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silicon (1)
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spectroscopy (1)
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tektites (1)
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weathering (1)
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sedimentary rocks
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sedimentary rocks
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chemically precipitated rocks
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ironstone (1)
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clastic rocks
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black shale (1)
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L chondrites
3. NOBLE GAS (AND OTHER) STUDIES ON METEORITES AND OTHER SAMPLES FROM FAR AWAY
ABSTRACT Although the ~200 impact craters known on Earth represent only a small fraction of the craters originally formed, the available data suggest an excess of craters by one order of magnitude, in number, in the interval ca. 470–440 Ma during the Ordovician. Most of these “excess” craters may be related to the breakup of the L-chondrite parent body (LCPB) in the asteroid belt at 465.8 ± 0.3 Ma. This is the only obvious peak in the crater-age record that can currently be attributed to an asteroid breakup and shower event. Spatial crater densities in regions with high potential for crater preservation (e.g., Canada and Scandinavia) support a one order-of-magnitude increase in the flux of large (>0.1 km) impactors following the LCPB breakup. A similar pattern as seen in the cratering record is emerging in studies of the flux of micrometeoritic chrome spinel through the Phanerozoic, with so far only one major spike in the flux, and associated with the LCPB breakup. Similarly, the record of K-Ar and (U-Th)/He gas retention ages of recently fallen meteorites only locates one major breakup, the LCPB event, during the Phanerozoic. On the other hand, astronomical backtracking studies of the orbits of asteroid family members indicate ~70 major family-forming breakups within the past ~540 m.y., which apparently have not left any clear imprint in Earth’s geological record. The chrome-spinel grains recovered in our studies dominantly represent large micrometeorites (>300 µm) and as such are also representative of the flux of larger meteorites to Earth. An observed, nearly constant flux of ordinary chondritic chrome-spinel grains throughout the Phanerozoic, except after the LCPB event, indicates that the present situation—with a clear dominance of ordinary chondritic matter in the large (>500 µm) micrometeorite and macroscopic meteorite fractions—has prevailed at least for the last 500 m.y. This is also supported by generally high ratios in our samples of chrome-spinel grains from ordinary chondrites compared to other types of spinel-bearing meteorites. The chrome-spinel data together with the abundance of fossil meteorites (1–21 cm in diameter) on the Ordovician seafloor also sets an upper limit at one order of magnitude on the increase in flux of large (>0.1-km-diameter) L-chondritic projectiles to Earth following the LCPB. Such an increase would not stand out in the global cratering record if ordinary chondritic impactors had only represented a small fraction of all Phanerozoic impactors. We argue that the origin of impactors delivered to Earth during the past 500 m.y. has mirrored the flux of large micrometeorites and meteorites, with ordinary chondrites being an important or, most likely, the dominant (in numbers) component throughout.
Space history of the High Possil and Strathmore meteorites from Ne and Ar isotopes
A high-pressure, clinopyroxene-structured polymorph of albite in highly shocked terrestrial and meteoritic rocks
Quantitative determination of the shock stage of L6 ordinary chondrites using X-ray diffraction
ABSTRACT Studies of impact structures in Sweden date back almost 60 years. They have so far resulted in the confirmation and understanding of eight impact structures and one impact-derived breccia layer, including the largest confirmed impact structure in the western part of Europe, the Siljan impact structure. Several additional structures have been proposed as impact derived, but they have to date not been confirmed. In this contribution, I summarize the current state of knowledge about the impact cratering record of Sweden. This is an up-to-date, comprehensive review of the features of known impact structures (and impact-related deposits) in Sweden. The described impact structures formed over a time period spanning from the Cambrian to the Cretaceous, and the preservation of several small (~1–2 km in diameter) Paleozoic impact structures indicates that the conditions securing their protection were close to optimal, with formation in a shallow epicontinental sea and rapid cover by protective sediments followed by a regional geologic evolution permitting their preservation. The generally well-preserved state of some of these crater structures contradicts the general assumption that such small impact structures can only be preserved for approximately a couple of thousand to a few million years. The Lockne-Målingen, Tvären, Granby, and Hummeln impact structures all have ages that place their formation in a period of proposed increased cratering rate on Earth following the breakup event of the L-chondrite parent body in the asteroid belt. However, to date, evidence other than a temporal correlation is missing for all of these structures except for Lockne (and Målingen), which has been shown to have formed by the impact of an L-chondritic body.
High-Pressure Phases in the Dhofar 922 L6 Chondrite: Crystallization of Olivine–Ringwoodite Aggregates and Jadeite from Melt
ABSTRACT We reconstructed a record of the micrometeorite flux in the Late Cretaceous using the distribution of extraterrestrial spinel grains across an ~2 m.y. interval of elevated 3 He in the Turonian Stage (ca. 92–90 Ma). From ~30 m of the limestone succession in the Bottaccione section, Italy, a total of 979 kg of rock from levels below and within the 3 He excursion yielded 603 spinel grains (32–355 μm size). Of those, 115 represent equilibrated ordinary chondritic chromite (EC). Within the 3 He excursion, there is no change in the number of EC grains per kilogram of sediment, but H-chondritic grains dominate over L and LL grains (70%, 27%, and 3%), contrary to the interval before the excursion, where the relation between the three groups (50%, 44%, and 6%) is similar to today and to the Early Cretaceous. Intriguingly, within the 3 He anomaly, there is also a factor-of-five increase of vanadium-rich chrome spinels likely originating from achondritic and unequilibrated ordinary chondritic meteorites. The 3 He anomaly has an unusually spiky and temporal progression not readily explained by present models for delivery of extraterrestrial dust to Earth. Previous suggestions of a relation to a comet or asteroid shower possibly associated with dust-producing lunar impacts are not supported by our data. Instead, the spinel data preliminary indicate a more general disturbance of the asteroid belt, where different parent bodies or source regions of micrometeorites were affected at the same time. More spinel grains need to be recovered and more oxygen isotopic analyses of grains are required to resolve the origin of the 3 He anomaly.
Near end-member shenzhuangite, NiFeS 2 , found in Muong Nong-type tektites from Laos
Discovery of asimowite, the Fe-analog of wadsleyite, in shock-melted silicate droplets of the Suizhou L6 and the Quebrada Chimborazo 001 CB3.0 chondrites
Dating phosphates of the strongly shocked Suizhou chondrite
Extraterrestrial dust, the marine lithologic record, and global biogeochemical cycles
Abstract The hydrological budget of the three major Asian rivers, namely the Indus, the Ganga and the Brahmaputra, is controlled by the Indian monsoon and Westerlies but their contribution in these basins are highly variable. Widely varying average annual precipitation has been reported within these basins. A poor network of in situ rain gauges, particularly in mountainous regions, inaccessible terrain, high variations in altitude and the significantly large size of basins forces adaption of satellite-based average annual precipitation. We investigate precipitation patterns for these three basins by using satellite-based Tropical Rainfall Measuring Mission (TRMM-3B42) data and compare and validate it with Asian Precipitation Highly Resolved Data Integration Towards Evaluation (APHRODITE) and India Meteorological Department (IMD) interpolated gridded precipitation data. The entire basins as well as basinal areas within the geographic limits of India have been considered. Our study shows that the precipitation broadly follows an east–west and north–south gradient control. The easternmost Brahmaputra Basin has the highest amount of precipitation followed by the Ganga Basin, and the westernmost Indus Basin has the least precipitation; precipitation is highest on the higher elevations than compared to lower elevations of the basins. A seasonal- and elevation-based approach is adapted to estimate snow precipitation and is discussed in terms of overall precipitation.