Results 211 to 220 of about 31,753 (257)

Discordant Zircon U–Pb Ages from the Uganda Basement

Nature Physical Science, 1971
FOR several years there has been controversy about the ages of the Uganda basement gneisses. Potassium–argon ages of micas from the basement rocks1 range from 600 to 415 m.y. whereas results for the apparently unconformably overlying Karagwe–Ankolean and Buganda–Toro sedimentary systems2,3 to the south (around the north end of Lake Victoria) suggest an
P. J. LEGGO, M. AFTALION, R. T. PIDGEON
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Zircon U-Pb ages for the Early Cambrian time-scale

Journal of the Geological Society, 1992
Single zircons from two Early Cambrian volcanic horizons have been analysed using the SHRIMP ion microprobe. Full details of the analytical procedures and data reduction are given. Zircons from tuff within the Lie de Vin Formation, near Tiout, Morocco, show little spread in U-Pb age and have a mean value of 521 ± 7 Ma (2σ).
Compston, W., Williams, I. S., Kirschvink, J. L., Zichao, Zhang, Guogan, Ma   +4 more
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Zircon UPb ages of Guyana greenstone-gneiss terrane

Precambrian Research, 1982
Abstract Isotopic UPb studies of zircons collected from weathered metagreywackes of the Barama-Mazaruni Supergroup of northern Guyana, South America, demonstrate an age of origin of ca. 2250 Ma. This is the best estimate for the age of the associated metavolcanic rocks.
Allan K. Gibbs, William J. Olszewski
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Tectonic Implications of U-Pb Zircon Ages of the Himalayan Orogenic Belt in Nepal

Science, 2000
Metasedimentary rocks of the Greater Himalaya are traditionally viewed as Indian shield basement that has been thrust southward onto Lesser Himalayan sedimentary rocks during the Cenozoic collision of India and Eurasia. Ages determined from radioactive decay of uranium to lead in zircon grains from Nepal suggest that Greater Himalayan protoliths were ...
, DeCelles, , Gehrels, , Quade, , LaReau, , Spurlin   +4 more
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Determination of U-Pb ages of zircons by direct measurement of the 210Pb/206Pb ratio

Chemical Geology, 1993
Abstract Precise measurements of the 210Pb/206Pb ratio in zircons permits, for the first time, the determination of complete U-Pb ages by measurement of Pb isotopes only, without determination of the U-Pb ratio by isotope dilution. The 238U daughter isotope 210Pb is generally in radioactive equilibrium with 238U; however, the very short half-life of ...
Wendt, I., Wendt, I., Tuttas, D.
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U‐Pb SIMS ages of Apollo 14 zircon: Identifying distinct magmatic episodes

Meteoritics & Planetary Science, 2019
AbstractU‐Pb ages of zircon in four different Apollo 14 breccias (14305, 14306, 14314, and 14321) were obtained by secondary ion mass spectrometry. Some of the analyzed grains occur as cogenetic, poikilitic zircon grains in lithic clasts, revealing magmatic events at ~4286 Ma, ~4200–4220 Ma, and ~4150 Ma.
F. Thiessen, A. A. Nemchin, J. F. Snape, M. J. Whitehouse   +3 more
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Solidification timescale for the Dufek Intrusion, Antarctica determined by U-Pb zircon ages

Geological Society of America Abstracts with Programs, 2019
<p>The 8-9 km thick Dufek layered mafic intrusion of Antarctica was emplaced at approximately 182 Ma associated with the Ferrar dolerites and the breakup of the supercontinent Gondwana.  It is rivaled in thickness only by the Bushveld Complex of South Africa and shows a similar progression in mineral compositions all
Jill VanTongeren, Aidan Taylor, Blair Schoene   +2 more
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Age constraint on Burmese amber based on U–Pb dating of zircons

Cretaceous Research, 2012
Amber from northern Myanmar has been commercially exploited for millennia, and it also preserves the most diverse palaeobiota among the worlds' seven major deposits of Cretaceous amber. Recent estimated ages vary from Albian to Cenomanian, based on palynology, an ammonoid, and Mesozoic insect taxa preserved within the amber. The burmite-bearing rock is
Guanghai Shi, David A. Grimaldi, George E. Harlow, Jing Wang, Jun Wang, Mengchu Yang, Weiyan Lei, Qiuli Li, Xianhua Li   +8 more
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U-Pb zircon age of the Rostberget W-occurrence, northern Sweden

Geologiska Föreningen i Stockholm Förhandlingar, 1989
Anomalously U-rich granites of the so-called Revsund type, associated with W- and Sn-enrichments, occur in the Gunnarn area close to Storuman in northern Sweden.
Kjell Billström, Björn Öhlander
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New U–Pb zircon ages and the duration and division of Devonian time

Earth and Planetary Science Letters, 1998
Newly determined U‐Pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the Devonian time-scale. They are: (1) 417:6 1:0 Ma for an ash within the conodont zone of Icriodus woschmidti=I. w. hesperius (early Lochkovian); (2) 408:3 1:9 Ma for an ash of early Emsian age correlated with the conodont zones of Po ...
R.D Tucker, D.C Bradley, C.A Ver Straeten, A.G Harris, J.R Ebert, S.R McCutcheon   +5 more
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