Partial record of a Miocene geomagnetic field excursion: Paleomagnetic data from the Paiute Ridge volcanic center, southern Nevada

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

OSTI ID:5128301

Ratcliff, C D; Geissman, J W; Perry, F V ^[1]; Crowe, B M ^[2]

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1. Univ. of New Mexico, Albuquerque, NM (United States)
2. Los Alamos National Lab., Las Vegas, NV (United States)

In the Palute Ridge area, northern Halfpint Range, a complex system of late Miocene (about 8.5 Ma) intrusive and extrusive alkaline mafic rocks crops out over an area of about 25km[sup 2]. Post-magmatic faulting and erosion have resulted in excellent exposure of this sub-volcanic center, allowing for a detailed study of mechanisms and timing of magma emplacement. Paleomagnetic data have been obtained from over 50 sites in mafic rocks, and host ash-flow tuffs and carbonate strata, to better understand the duration of magmatic activity. Magnetizations, isolated in progressive alternating field and thermal demagnetization, for most of the sites at Palute Ridge deviate significantly from expected directions for a time-averaged late Miocene field. Demagnetization data show that there are two types of sample behavior. First, samples with close to expected reverse polarity directions (e.g., the chilled margin of a sill, D=209.2, l=[minus]36.4, [alpha]95=13.2, N=5, k=34.8). Second, and far more common, are samples giving magnetizations of southwest to northwest declination, with both shallow to moderate positive and negative inclination. Within this second grouping are several sites, including syenite pods which differentiated in situ from a large lopolith, having mean declinations that are due west and of shallow inclination. Contact tests performed at several sites are positive and show a clear correlation between sample position and isolated remanence direction. The authors preferred interpretation of the anomalously directed magnetization is that these rocks acquired a TRM during either a high amplitude excursion, or the transitional portion of a field reversal. Thermal models based on larger intrusions [+-] 10m thick at Paiute Ridge indicate that the magmas could cool through estimated magnetization blocking temperatures within weeks or months of emplacement.

• OSTI ID: 5128301
• 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
CENOZOIC ERA
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
IGNEOUS ROCKS
MAGNETISM
NEVADA
NORTH AMERICA
PALEOMAGNETISM
PETROGENESIS
PETROLOGY
ROCKS
TERTIARY PERIOD
USA
VOLCANIC ROCKS