Proterozoic geochronologic and isotopic boundary in NW Arizona

Journal Article · Tue May 01 04:00:00 EDT 1990 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629412· OSTI ID:6250117

Chamberlain, K R; Bowring, S A ^[1]

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1. Washington Univ., St. Louis, MO (USA)

U-Pb ages determined from zircon, sphene, and apatite in conjunction with Pb isotopic analyses of alkali feldspar establish a regional geochronological framework and constrain the location of a major north-trending Proterozoic crustal boundary in northwestern Arizona. Two regions west of the boundary (Hualapai Mountains and Lost Basin Range-Garnet Mountain) are characterized by complex U-Pb zircon systematics, evidence for inheritance of an older zircon component (1.8-2.3 Ga), and elevated {sup 207}Pb/{sup 204}Pb from feldspars compared to the east. Although the discordia patterns are complex, supracrustal rocks are interpreted to be ca. 1.73 Ga and are intruded by plutonic rocks ca. 1.70 Ga. Deformation is younger than ca. 1.70 Ga foliated granites and older than the 1,682 {plus minus} 4 Ma Garnet Mt. monzogranite. The rocks in one area east of the boundary (Cottonwood Cliffs) are characterized by relatively simple U-Pb zircon systematics, no evidence for inheritance of any older component, and feldspar {sup 207}/{sup 204}Pb near model mantle values. Supracrustal rocks are older than 1.73 Ga, as they are intruded by a 1,730 {plus minus} 9 Ma foliated granodiorite. Timing of deformation is constrained by the late syn-kinematic Valentine granite dated at 1,713 {plus minus} 12 Ma. Mineral ages indicate that the rocks on either side of the boundary had different cooling histories and inferentially, different uplift histories. West of the boundary, the cooling history is inferred from minerals separated from an amphibolite: metamorphic zircon is 1,687 +13/{minus}8 Ma, sphene is 1,660 {plus minus} 5 Ma, hornblende has a {sup 40}Ar/{sup 39}Ar age of 1,552 {plus minus} 5 Ma, and apatite has a U-Pb age of 1,520 {plus minus} 45 Ma. East of the boundary an amphibolite has sphene with an age of 1,670 {plus minus} 11 Ma and apatite with an age of 1,630 {plus minus} 8 Ma.

• OSTI ID: 6250117
• Journal Information: Journal of Geology; (USA), Journal Name: Journal of Geology; (USA) Vol. 98:3; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDE ISOTOPES
AGE ESTIMATION
ALPHA DECAY RADIOISOTOPES
AMPHIBOLE
APATITES
ARIZONA
BOUNDARY CONDITIONS
CONTINENTAL CRUST
COOLING
DEFORMATION
EARTH CRUST
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION IX
FELDSPARS
GEOLOGIC AGES
GEOLOGIC HISTORY
GRANITES
HEAVY NUCLEI
HORNBLENDE
HOURS LIVING RADIOISOTOPES
IGNEOUS ROCKS
ISOMERIC TRANSITION ISOTOPES
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LEAD 204
LEAD 207
LEAD ISOTOPES
MINERALS
MOUNTAINS
NORTH AMERICA
NUCLEI
OXYGEN COMPOUNDS
PHOSPHATE MINERALS
PLUTONIC ROCKS
PRECAMBRIAN ERA
RADIOISOTOPES
ROCKS
SECONDS LIVING RADIOISOTOPES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
TITANITE
TRANSITION ELEMENT COMPOUNDS
URANIUM ISOTOPES
USA
YEARS LIVING RADIOISOTOPES
ZIRCON
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES