Geochronology, geochemistry, and petrology of the Precambrian Sandia granite, Albuquerque, New Mexico

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1985

OSTI ID:6955928

Majumdar, A

The Precambrian Sandia granite of north-central New Mexico belongs to the 1.2-1.6 Ga crustal province of the western USA. The granite shows an intrusive contact with the metamorphic country rocks. The Rb-Sr whole rock isochron age of the country rocks is 1.61 +/- 0.06 Ga, (/sup 87/Sr//sup 86/Sr)/sub 0/ = 0.705 +/- 0.001. The culmination of the intrusion of the Sandia granite took place at 1.44 +/- 0.04 GA. (/sup 87/Sr//sup 86/)/sub 0/ = 0.7054 +/- 0.0005. Rb-Sr ages on biotite-whole rock pairs and an /sup 40/Ar//sup 39/Ar dating of a biotite from the granite indicate final cooling to 300-350/sup 0/C at 1.33 Ga. This suggests slow cooling of the granite at rates which averaged 4/sup 0/C/Ma for about 100 Ma after its emplacement; during this period the Rb-Sr isotope system perhaps remained partially open. The Sandia granite shows compositional variation from granodiorite to quartz monzonite in both the northern and southern blocks. The field geology, petrology, and geochemistry of the two blocks suggest that they form a single pluton. Both the Sandia granite and mesocratic, two pyroxene granulite xenoliths therein give an ..delta../sup 18/O value of +8.0 +/- 0.5% indicating (meta)igneous source ricks for each of them. These values tend to rule out Condie's (1978) favored hypothesis for magma generation of 30-50% partial melting of siliceous gradulites. Rather, they favor an alternative hypothesis, equally satisfactory from the geochemical viewpoint, involving 5-10% melt of a gabbroic or two-pyroxene granulite parent rock in the lower crust. The Sandia granite, and by implication, the other high-Ca granitic rocks of the western USA thus do not seem to represent addition of new mantle-derived materials to the middle-late Proterozoic crust of this section of the continent.

• Research Organization: Louisiana State Univ., Baton Rouge (USA)
• OSTI ID: 6955928
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
580400 -- Geochemistry-- (-1989)
CHEMICAL COMPOSITION
CHEMISTRY
FEDERAL REGION VI
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGY
GRANITES
IGNEOUS ROCKS
ISOTOPE RATIO
MINERALS
NEW MEXICO
NORTH AMERICA
ORIGIN
PETROLOGY
PLUTONIC ROCKS
PRECAMBRIAN ERA
ROCKS
USA