Results 191 to 200 of about 5,596 (229)

Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks

Nature Geoscience, 2013
The Archaean rocks of Isua, West Greenland, contain graphite, but its origins are debated. Geochemical and microscopic analyses suggest that the graphite was formed from biologically formed carbon that was deposited at least 3.7 billion years ago.
Ohtomo, Yoko, Kakegawa, Takeshi, Ishida, Akizumi, Nagase, Toshiro, Rosing, Minik Thorleif   +4 more
openaire   +2 more sources

Whole-Rock Rb-Sr Age of Metasedimentary Rocks Below the Stillwater Complex, Montana

Geological Society of America Bulletin, 1969
Eight metasedimentary rocks selected from a suite collected below the Stillwater Complex in the Beartooth Mountains, Montana, yield a whole-rock Rb-Sr age of 2730 ± 150 m.y. (λ = 1.39 × 10 −11 /yr). The samples represent rocks located 0.4 to 6 miles from the lower contact of the Complex, and the nearer samples are definitely within the contact ...
J. L. POWELL, W. R. SKINNER, DAVID WALKER   +2 more
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Fold growth and transposition in metasedimentary rocks of the southeastern Adirondacks: Summary

Geological Society of America Bulletin, 1980
INTRODUCTION Most of the estimates of the pressure and temperature for Adirondack metamorphism fall in the range of 650 to 800 °C and 7 to 9 kbar (Whitney and McLelland, 1973; Essene and others, 1977; Boone, 1978; Valley and Bohlen, 1979; Whitney and others, 1979), suggesting an elevated geothermal gradient comparable to oceanic gradients (Mercier and
JAMES W. GRANATH, NOEL BARSTOW
openaire   +1 more source

MICROSTRUCTURES AND COMPOSITION OF ANATECTIC MELT INCLUSIONS IN METASEDIMENTARY ROCKS

2011
Melt inclusions (MI) investigation represents a widely used approach to gain information on a number of igneous processes on the Earth system. The recent finding of crystallized and glassy MI in high-grade, partially melted metapelites and metagraywackes opened up the possibility to investigate also anatectic processes with the same method. The present
Ferrero S, Bartoli O, Cesare B, Salvioli Mariani E, AcostaVigil A, Cavallo A, Groppo C, Battiston S   +7 more
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Late Precambrian Metasedimentary Rocks of Egan Range, Nevada

AAPG Bulletin, 1963
ABSTRACT Approximately 8,450 feet of polymetamorphic Late Precambrian strata are exposed at Heusser Mountain in the central northern Egan Range, Nevada. These rocks were regionally metamorphosed to slates, argillites, phyllites, metasiltstones, and quartzites; they were later contact-metamorphosed to grades as high as the biotite-zone
openaire   +1 more source

Geochemistry and sedimentology of Grampian Group metasedimentary rocks, Upper Strathspey

Scottish Journal of Geology, 1989
Synopsis The sedimentological attributes of the metasedimentary rocks of Upper Strathspey are inferred from their major and trace element geochemistry. The rocks of the Glenshirra Succession have high oxidation ratios and are of a lithic nature which suggests shallow water, probably alluvial, environments.
openaire   +1 more source

Microtextural analyses of detrital zircon for paleoenvironmental interpretations of metasedimentary rocks

Geology
Abstract Sedimentary rocks archive the history of Earth’s surface. However, alteration by diagenesis, weathering, deformation, and metamorphism makes interpretating Earth’s earliest environments challenging and ambiguous. We show that detrital zircon grains preserve an unaltered account of transport history, even in billion-year-old ...
M. Colin Marvin, Michael Hasson, Vittorio Colicci, Raisha Abubo, Mathieu G.A. Lapôtre   +4 more
openaire   +1 more source

Rb-Sr Dating of Middle Precambrian Metasedimentary Rocks of Minnesota

Geological Society of America Bulletin, 1966
Rb-Sr dating of middle Precambrian metasedimentary rocks of central and northern Minnesota indicates a loss of radiogenic strontium during regional metamorphism. Samples of the Mahnomen Formation yield two distinct isochrons of 1.75 and 1.46 b.y. Samples dated at 1.46 b.y.
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Fold Growth and Transposition in Metasedimentary Rocks of the Southeastern Adirondacks

GSA Bulletin, 1980
James W. Granath, Noel Barstow
openaire   +1 more source

of Archean clastic metasedimentary rocks: a petrogenetic indicator for Archean gneisses?

Geochimica et Cosmochimica Acta, 1977
Frederick J. Longstaffe, Henry P. Schwarcz   +1 more
openaire   +1 more source