Samarium-neodymium and rubidium-strontium isotopic studies of the origin and evolution of continental crust
Part I. Nd model ages of Precambrian granites from the U.S. midcontinent define crust-formation age provinces that young to the south. Much of this crust formed 1.7 to 1.9 b.y. ago. Patterns of continental growth deduced from this study emphasize the episodicity of crust formation, and suggest an average ago of 2.2 b.y. for the continent. Part II. Initial /sup 143/Nd//sup 144/Nd ratios of 1700 myr greenstones from the southwestern U.S. range from epsilon/sub Nd/ = +3.3 to +6.5, the highest values yet observed for mid-Proterozoic rocks. The change in epsilon/sub Nd/ of depleted mantle has been only 2 to 3 epsilon units over the past 1700 myr. This supports hypotheses of significant recycling of continental crust back into the mantle. Part III. Isotopic paleodietary analyses of bone assume that post-mortem alteration has not changed original values. To test this, bone isotopic compositions of modern and prehistoric animals were analyzed. /sup 87/Sr//sup 86/Sr, /sup 18/O//sup 16/O and /sup 13/C//sup 12/C in inorganic phases of bone were modified during diagenesis, whereas /sup 15/N//sup 14/N and /sup 13/C//sup 12/C ratios in collagens were not affected. Part IV. Tertiary sediments from northern New Mexico were studied in order to compare Nd isotopic and petrographic techniques of provenance determination. If source areas are isotopically distinct, Nd model ages provide provenance information not reflected in the petrographic data, and are useful in cases where other provenance indicators are unavailable. Part V. Initial epsilon/sub Nd/ and epsilon/sub Sr/ values of eclogite, blueschist and greenstone blocks from the Franciscan Complex, California, cluster around +8 to +10, and -3 to +11, respectively. This suggests a protolith of hydrothermally-altered oceanic basalt.
- Research Organization:
- California Univ., Los Angeles (USA)
- OSTI ID:
- 6997226
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CONTINENTAL CRUST
GEOLOGIC HISTORY
ORIGIN
USA
AGE ESTIMATION
BONE CELLS
CALIFORNIA
CARBON 12
CARBON 13
DIAGENESIS
FOSSILS
GRANITES
ISOTOPE DATING
ISOTOPE RATIO
NEODYMIUM 143
NEODYMIUM 144
NEW MEXICO
NITROGEN 14
NITROGEN 15
OXYGEN 16
OXYGEN 18
PETROGRAPHY
STRONTIUM 86
STRONTIUM 87
ALKALINE EARTH ISOTOPES
ALPHA DECAY RADIOISOTOPES
ANIMAL CELLS
BETA DECAY RADIOISOTOPES
CARBON ISOTOPES
CONNECTIVE TISSUE CELLS
EARTH CRUST
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION IX
FEDERAL REGION VI
HOURS LIVING RADIOISOTOPES
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
LIGHT NUCLEI
NEODYMIUM ISOTOPES
NITROGEN ISOTOPES
NORTH AMERICA
NUCLEI
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
OXYGEN ISOTOPES
PLUTONIC ROCKS
RADIOISOTOPES
RARE EARTH NUCLEI
ROCKS
SOMATIC CELLS
STABLE ISOTOPES
STRONTIUM ISOTOPES
YEARS LIVING RADIOISOTOPES
580100* - Geology & Hydrology- (-1989)