Nd isotopes and the origin of Grenville-age rocks in Texas: Implications for Proterozoic evolution of the United States mid-continent region

Journal Article · Wed Nov 01 00:00:00 EST 1989 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629352· OSTI ID:7135892

Patchett, P J; Ruiz, J ^[1]

---

1. Univ. of Arizona, Tucson (USA)

Nd isotopic data were obtained for Precambrian Grenville-belt rocks in Texas. The samples represent most components of the crust of the Llano, Van Horn, and Franklin Mountains exposed terranes. Almost all Precambrian igneous, metamorphic, and sedimentary rocks from the three regions document addition to North America of mantle-derived crustal materials in the 1.6-1.0 Ga interval. The exception is a quartzite from the westernmost (Franklin Mountains) exposure, which was derived from {approximately}1.8 Ga crust of the southwestern United States. The initial {epsilon}{sub Nd} values of all rocks except the quartzite lie in the +1 to +6 range for igneous/metamorphic ages of 1.37 to 1.06 Ga. These results can be interpreted in two ways: (1) as documenting 0-20% additions of older crustal material to mantle-derived products 1.4-1.0 Ga ago; or (2) as documenting derivation of the Grenville exposures by recycling of older crustal protoliths separated from the mantle 1.6-1.3 Ga ago. The Nd data in isolation do not resolve these two interpretations. The model mantle separation ages (T{sub DM}) of the rocks are very similar to published values of granulites in Mexico and Virginia: all these regions of the United States and Mexico show a strong peak of T{sub DM} around 1.4 Ga ago. If the ages represent older crustal protoliths, then they would have formed coevally with the 1.5-1.3 Ga Granite-Rhyolite Terranes of the continental interior USA. This would imply that the Granite-Rhyolite Terranes were formed during orogenic/accretionary processes in the adjoining Grenville Belt, and are not anorogenic in association, as conventionally assumed.

• OSTI ID: 7135892
• Journal Information: Journal of Geology; (USA), Vol. 97:6; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GEOLOGIC DEPOSITS
AGE ESTIMATION
TEXAS
CONTINENTAL CRUST
GEOLOGIC HISTORY
GEOLOGIC MODELS
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
METAMORPHIC ROCKS
MOUNTAINS
NEODYMIUM
SEDIMENTARY ROCKS
EARTH CRUST
ELEMENTS
FEDERAL REGION VI
METALS
NORTH AMERICA
RARE EARTHS
ROCKS
USA
580000* - Geosciences