Other
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmgp11b0828b&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #GP11B-0828
Other
9360 South America, 1035 Geochronology, 1535 Reversals (Process, Timescale, Magnetostratigraphy)
Scientific paper
Lava flows in Quebrada Turbia, Tatara San Pedro Volcanic Complex, central Chile (36S, 289E), preserve a detailed record of what was presumed to be the Matuyama-Brunhes geomagnetic reversal. Sampling in the west wall of the valley yields reverse and transitional polarity flows; two km to the north, another section yields 17 transitional flows from the same sequence overlain by flows with normal polarity. 40Ar/39Ar incremental heating experiments on lavas of the two sections provide 9 independent age determinations and yield a weighted mean of 792 ka for the magnetic transition. Alternating field and thermal demagnetization, rock magnetic analyses, and petrographic observations indicate primary magnetization carried by titanomagnetite. The polarity change is characterized by a jump from reverse poles to poles clustered over Australia, followed by a jump to normal polarity latitudes. Magnetization of these lavas is consistent with either a brief period when the field was dominated by a subequatorial dipole, or a more complex non-dipolar field that may reflect the influence of a long-lived regional lower mantle control over a weakened dynamo. The Quebrada Turbia lavas are ca. 16 kyrs older than those recording the reversal at Haleakala volcano, Maui. Moreover, the 792 ka age of the Chilean lavas is older than most astronomical estimates for the Matuyama-Brunhes reversal suggesting that this section may record a precursor to the actual field reversal, seen in low paleointensities from more than a dozen marine sediment cores.
Brown Laurel
Jicha B.
Pickens Jeremy
Singer Brad
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