Matches in SemOpenAlex for { <https://semopenalex.org/work/W2071111570> ?p ?o ?g. }
- W2071111570 endingPage "10680" @default.
- W2071111570 startingPage "10663" @default.
- W2071111570 abstract "The presence of Archean granite forming the core of an updomed and overturned sequence of strata at Vredefort, South Africa, has been known for over 70 years. Recent geophysical, geochemical, and geological evidence has given rise to the proposal that the basement granite core has also been overturned, presenting a section of the earth's granitic crust to view and that radial traverses in the Vredefort basement penetrate through a ∼15 km thick section of the Archean crust, when moving from the contact of collar strata to the center of the dome. The upper levels of the Vredefort crust are dominated by a relatively homogeneous outer granite gneiss (OGG) displaying marked gradients in large ion lithophile elements. These rocks grade inward into the deeper levels which occur in granulite facies metamorphism. The deeper levels of the Vredefort crust exposed in the central parts of the dome consist predominantly of felsic Inlandsee Leucogranofels (ILG) which occurs interleaved with inclusions of mafic metavolcanic and metasedimentary rocks termed Steynskraal Metamorphic Zone (SMZ). A comprehensive isotopic study using four decay schemes (87Rb, 232Th, 238U, and 235U) on this crustal section is now reported. The results permit unique and direct tests on the theories of Archean crust forming processes. In the upper Vredefort crust, whole rock isochron ages of ∼3050 m.y. are obtained from the four decay schemes, and almost all evidence of an extended crustal history prior to ∼3050 m.y. has been obliterated. Establishment of strong vertical gradients in Rb/Sr ratio, shortly before ‘setting’ of Rb-Sr whole rock systems, has wide implications for the interpretation of Sr initial ratios. Although the Vredefort upper levels of the crust has a low 87Sr/86Sr initial ratio of 0.7019 ± 0.0002, it probably participated in a crustal prehistory for at least 500 m.y. In the deeper levels of the Vredefort basement the geochronology is much more complex. Rb-Sr and Th-Pb isochrons of ∼3500 m.y. are recorded in the mafic granulite relicts. A companion paper (Welke and Nicolaysen, this issue) provides evidence for an early crust-forming event in this sector ∼3800 m.y. ago. From ∼3500 m.y. onward, these deeper crustal levels did not undergo addition of new Archean crust-forming material on a major scale. Nevertheless, a most important younger Archean event affected these levels ∼2800 m.y. ago: cessation of high-grade metamorphism is recorded by setting of the Rb-Sr isotopic system in the felsic rocks and zircon U-Pb ages; an episode of strong uranium depletion affected both the felsic and mafic rocks of this sector ∼2800 m.y. ago. The Inlandsee Leucogranofels is evidently a rock unit with a long and complex history, beginning with the emplacement as a crustal unit at least 3800 m.y. ago. Since then it has been subject to reworking and resetting of isotopic systems which terminated ∼2800 m.y. ago. In the deeper crust there is scant evidence of a 3050 m.y. event. Similarly, there is no record of a ∼2800 m.y. old imprint in the upper Vredefort crust. Thus, the last major events that affected the geochemical constitution of the Vredefort upper and deeper crustal sectors differed in time and nature; nevertheless, they brought about isotopic setting in a downward moving sequence, while the overlying crust remained cooler, rigid, and unaffected. These events probably reflect significant discontinuities in the cooling of the Archean crust." @default.
- W2071111570 created "2016-06-24" @default.
- W2071111570 creator A5041323157 @default.
- W2071111570 creator A5068610485 @default.
- W2071111570 creator A5079112571 @default.
- W2071111570 date "1981-11-10" @default.
- W2071111570 modified "2023-09-25" @default.
- W2071111570 title "Geochronology of the deep profile through archean basement at Vredefort, with implications for early crustal evolution" @default.
- W2071111570 cites W1549422452 @default.
- W2071111570 cites W1964460216 @default.
- W2071111570 cites W1964789174 @default.
- W2071111570 cites W1965858395 @default.
- W2071111570 cites W1966673879 @default.
- W2071111570 cites W1968718505 @default.
- W2071111570 cites W1970680726 @default.
- W2071111570 cites W1971513400 @default.
- W2071111570 cites W1971632964 @default.
- W2071111570 cites W1972406462 @default.
- W2071111570 cites W1974091969 @default.
- W2071111570 cites W1976011966 @default.
- W2071111570 cites W1976216916 @default.
- W2071111570 cites W1978168422 @default.
- W2071111570 cites W1981940640 @default.
- W2071111570 cites W1984520040 @default.
- W2071111570 cites W1987717268 @default.
- W2071111570 cites W1988359105 @default.
- W2071111570 cites W1990949866 @default.
- W2071111570 cites W2007060519 @default.
- W2071111570 cites W2007105153 @default.
- W2071111570 cites W2009617051 @default.
- W2071111570 cites W2011420263 @default.
- W2071111570 cites W2026472177 @default.
- W2071111570 cites W2026631963 @default.
- W2071111570 cites W2028875489 @default.
- W2071111570 cites W2031561542 @default.
- W2071111570 cites W2051919739 @default.
- W2071111570 cites W2059245554 @default.
- W2071111570 cites W2065064863 @default.
- W2071111570 cites W2075321980 @default.
- W2071111570 cites W2076022602 @default.
- W2071111570 cites W2077670882 @default.
- W2071111570 cites W2078831561 @default.
- W2071111570 cites W2081030419 @default.
- W2071111570 cites W2081740788 @default.
- W2071111570 cites W2082859047 @default.
- W2071111570 cites W2083774164 @default.
- W2071111570 cites W2090666476 @default.
- W2071111570 cites W2095580753 @default.
- W2071111570 cites W2097328061 @default.
- W2071111570 cites W2100575321 @default.
- W2071111570 cites W2114276383 @default.
- W2071111570 cites W2121429788 @default.
- W2071111570 cites W2124515580 @default.
- W2071111570 cites W2145604970 @default.
- W2071111570 cites W2156931605 @default.
- W2071111570 doi "https://doi.org/10.1029/jb086ib11p10663" @default.
- W2071111570 hasPublicationYear "1981" @default.
- W2071111570 type Work @default.
- W2071111570 sameAs 2071111570 @default.
- W2071111570 citedByCount "84" @default.
- W2071111570 countsByYear W20711115702012 @default.
- W2071111570 countsByYear W20711115702014 @default.
- W2071111570 countsByYear W20711115702016 @default.
- W2071111570 countsByYear W20711115702018 @default.
- W2071111570 countsByYear W20711115702019 @default.
- W2071111570 countsByYear W20711115702020 @default.
- W2071111570 countsByYear W20711115702021 @default.
- W2071111570 countsByYear W20711115702023 @default.
- W2071111570 crossrefType "journal-article" @default.
- W2071111570 hasAuthorship W2071111570A5041323157 @default.
- W2071111570 hasAuthorship W2071111570A5068610485 @default.
- W2071111570 hasAuthorship W2071111570A5079112571 @default.
- W2071111570 hasConcept C109007969 @default.
- W2071111570 hasConcept C112764850 @default.
- W2071111570 hasConcept C127313418 @default.
- W2071111570 hasConcept C127413603 @default.
- W2071111570 hasConcept C141646446 @default.
- W2071111570 hasConcept C146588470 @default.
- W2071111570 hasConcept C147176958 @default.
- W2071111570 hasConcept C149347711 @default.
- W2071111570 hasConcept C151730666 @default.
- W2071111570 hasConcept C167284885 @default.
- W2071111570 hasConcept C171701179 @default.
- W2071111570 hasConcept C17409809 @default.
- W2071111570 hasConcept C18142444 @default.
- W2071111570 hasConcept C193429443 @default.
- W2071111570 hasConcept C202746551 @default.
- W2071111570 hasConcept C26687426 @default.
- W2071111570 hasConcept C2776698055 @default.
- W2071111570 hasConcept C2780356177 @default.
- W2071111570 hasConcept C2781297371 @default.
- W2071111570 hasConcept C42787717 @default.
- W2071111570 hasConcept C46381822 @default.
- W2071111570 hasConcept C487381 @default.
- W2071111570 hasConceptScore W2071111570C109007969 @default.
- W2071111570 hasConceptScore W2071111570C112764850 @default.
- W2071111570 hasConceptScore W2071111570C127313418 @default.
- W2071111570 hasConceptScore W2071111570C127413603 @default.