Paleomagnetic reversals in Miocene dikes, and tectonic evolution of the Crossman block, Mohave Mountains, Arizona

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5022330

Nielson, J E; Nakata, J K ^[1]; Pease, V L

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1. Geological Survey, Menlo Park, CA (United States)

Paleomagnetic data, isotopic ages, and compositions all suggest a common, coeval magmatic source for early Miocene volcanic rocks and a large dike swarm in the Crossman block (CB), central Mohave Mountains, AZ, Colorado River extensional corridor. The CB is a coherent 12-to-15-km-thick piece of crust in the upper plate of the Whipple detachment fault, which tilted by 90 to 100 to the SW in response to movements on the fault. A swarm of early Miocene dikes dip shallowly to the NE, and account for 20% or more of CB thickness. Compositions of dikes and lavas from the CB ranged from basaltic to rhyolitic. A calk-alkaline trend is evident in spite of widespread alteration, and a few of the dikes can be traced into the flow sequence. Reliable dike ages are between 20 and 18 Ma, and those for lavas range from 21.5 to 17.9 Ma. Dikes in the CB show both normal and reversed magnetic polarities contained in high temperature and high coercivity components. Tests of stability in a baked contact supports a Miocene age for the magnetizations. This interpretation supports and adds detail to a two-stage model for tilting of the CB at 19.9[+-]0.5 Ma, based on an unconformity in the volcanic stratigraphy. An explanation for such a rapid tilting of a large crustal fragment may be that friction between lower and upper plate was lowered by a large volumes of magmas that either were generated or ponded at the level of the Whipple detachment fault, at about 20 Ma.

• OSTI ID: 5022330
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ARIZONA
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPED COUNTRIES
DIKES
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
IGNEOUS ROCKS
ISOTOPE DATING
MAGMATISM
MAGNETISM
MIOCENE EPOCH
NORTH AMERICA
ORIGIN
PALEOMAGNETISM
ROCKS
TECTONICS
TERTIARY PERIOD
USA
VOLCANIC ROCKS