Plutonic and metamorphic xenoliths from the Cascada Tuff, Chihuahua, Mexico, as evidence indicating the composition of the basement rocks beneath the Sierra Madre Occidental

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6875164

Duex, T W

The Sierra Madre Occidental of western Mexico is composed dominantly of Mid-Tertiary felsic and subordinate mafic volcanic rocks with only sparse outcrops of non-volcanic rocks. There are widely scattered but small exposure of plutonic rocks but regionally metamorphosed rocks are not known to occur in the Sierra. To this date the only known area where plutonic and metamorphic xenoliths have been found is near the village of Basaseachic in western Chihuahua where thick outcrops of the Cascada Tuff occur. The xenoliths are the only known occurrence of regionally metamorphosed rocks for a distance of about 400 km between exposures of Precambrian rocks to the west in Sonora and the east in central Chihuahua. Non-volcanic xenoliths from a few cm to about one meter in diameter occur most abundantly in the upper portions of the Cascada Tuff. They can be divided into four main groups in decreasing order of abundance as follows: (1) coarse-grained phaneritic felsic igneous rocks; (2) cataclastically deformed plutonic rocks; (3) fine-grained phaneritic, mafic to intermediate igneous rocks; and (4) low-grade schistose, gneissic, and non-foliated metamorphic rocks. The lithological composition of the xenoliths is grossly similar to that described for Precambrian metamorphic and plutonic rocks from northern Mexico and the southwestern US.

• Research Organization: Univ. of Southern Louisiana, Lafayette (USA)
• OSTI ID: 6875164
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
BASEMENT ROCK
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPING COUNTRIES
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
LATIN AMERICA
LITHOLOGY
METAMORPHIC ROCKS
MEXICO
NORTH AMERICA
PETROLOGY
PLUTONIC ROCKS
ROCKS
TERTIARY PERIOD
TEXTURE
TUFF