Nd-Sr isotopic provenance analysis of Upper Cretaceous Great Valley fore-arc sandstones
- Univ. of California, Los Angeles (United States)
- Lawrence Berkeley Lab., CA (United States)
The provenance of fore-arc sandstones of the Upper Cretaceous Great Valley Group was investigated by using measurements of Sm-Nd and Rb-Sr isotope ratios and major and trace element concentrations. The objective was to elucidate the erosional history of the adjacent Sierra Nevada arc and its relation to magmatism and fore-are sedimentation. Relatively detailed provenance information is obtainable because the currently exposed plutonic rocks of the arc (and, by inference, the Cretaceous volcanic rocks) have large geographic gradients in isotopic composition, mainly from west to east across the arc. The relation of {epsilon}{sub Nd} to {epsilon}{sub Sr} and to major and trace elements in Great Valley sandstones is the same as in the plutonic rocks of the Sierra Nevada; this observation confirms that the arc was the primary source of sediment and that the chemistry of the detritus was not significantly disturbed by sedimentary processes. With decreasing {epsilon}{sub Nd}, there is an increase in K{sub 2}O, Rb, Pb, Ba, La, and U, and MgO, Ni, and Cr decrease. The {epsilon}{sub Nd} of sandstones decreases with decreasing depositional age from {minus}0.7 to {minus}5.0 in 97 to 73 Ma strata. The {epsilon}{sub Nd} and age of the sandstones closely match those of the plutonic rocks of the Sierra Nevada. This observation indicates that the location of the mean sandstone source and the active volcanic front were nearly coincident in time and space; thus, the isotopic compositions of the sandstones directly record the temporal and geographic variations in arc magmatism. The volcanic roof of the Sierra Nevada arc was evidently chemically and isotopically equivalent to its plutonic roots. Prearc metasedimentary rocks did not significantly contribute to the isotopic or geochemical composition of the fore-arc sandstone.
- OSTI ID:
- 5941863
- Journal Information:
- Geology; (United States), Journal Name: Geology; (United States) Vol. 19:8; ISSN GLGYB; ISSN 0091-7613
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ACTINIDES
AGE ESTIMATION
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
ALKALI METALS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
BARIUM
CALIFORNIA
CHALCOGENIDES
CHEMISTRY
CHROMIUM
CRETACEOUS PERIOD
DEVELOPED COUNTRIES
ELEMENTS
EROSION
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
LANTHANUM
LEAD
MAGMATISM
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MESOZOIC ERA
METALS
NEODYMIUM ISOTOPES
NICKEL
NORTH AMERICA
ORIGIN
OXIDES
OXYGEN COMPOUNDS
PLUTONIC ROCKS
POTASSIUM COMPOUNDS
POTASSIUM OXIDES
RARE EARTH ISOTOPES
RARE EARTHS
ROCKS
RUBIDIUM
RUBIDIUM ISOTOPES
SAMARIUM ISOTOPES
SANDSTONES
SEDIMENTARY ROCKS
SEDIMENTATION
SOURCE ROCKS
STRONTIUM ISOTOPES
TRANSITION ELEMENTS
URANIUM
USA
VALLEYS
VOLCANISM