Refining the Quaternary Geomagnetic Instability Time Scale (GITS); lava flow recordings of the Blake and post-Blake excursions

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doi: 10.1016/j.quageo.2012.12.005
Author(s): Singer, Brad S.; Guillou, Hervé; Jicha, Brian R.; Zanella, Elena; Camps, Pierre
Author Affiliation(s): Primary:
University of Wisconsin-Madison, Department of Geoscience, Madison WI, United States
Institut Pierre Simon Laplace, France
Universitá di Torino, Italy
Université Montpellier II, France
Volume Title: Advance in <sup>40</sup>Ar/<sup>39</sup>Ar dating of Quaternary events and processes
Volume Author(s): Singer, Brad S., editor; Renne, Paul R.
Source: Advance in >40`Ar/>39`Ar dating of Quaternary events and processes, edited by Brad S. Singer and Paul R. Renne. Quaternary Geochronology, Vol.21, p.16-28. Publisher: Elsevier, Amsterdam, International. ISSN: 1871-1014
Note: In English. 63 refs.; illus., incl. sketch maps, 3 tables, strat. col.
Summary: The Blake excursion was among the first recognized with directional and intensity behavior known mainly from marine sediment and Chinese loess. Age estimates for the directional shifts in sediments are poorly constrained to about 118-100 ka, i.e., at the marine isotope stage (MIS) 5e/5d boundary. Moreover, sediments at Lac du Bouchet maar, France and along the Portuguese margin reveal what may be a "post-Blake" excursion at about 105-95 ka. The excursional directions are associated with a prominent paleointensity minimum between about 125 and 95 ka in global stacked records. Lava flow recordings of the Blake excursion(s) have, however, been questionable because precise ages required for correlation with these sediment records are lacking. To establish new, independent records of the Blake excursion, and link these into a larger Quaternary GITS, we have undertaken 40Ar/39Ar incremental heating and unspiked K-Ar experiments on groundmass from the transitionally magnetized Inzolfato flow on Lipari Island. We also obtained 40Ar/39Ar incremental heating results for a lava flow on Amsterdam Island originally thought to record the Mono Lake excursion and from the transitionally magnetized El Calderon basalt flow, New Mexico that was K-Ar dated by Champion et al. (1988) at 128 ± 66 ka. Unspiked K-Ar ages of four samples from the Inzolfato flow are 102.5 ± 4.7, 101.3 ± 3.3, 97.1 ± 2.6, and 96.8 ± 3.1 ka and thus indistinguishable from one another. 40Ar/39Ar results are more complex, with three samples yielding discordant age spectra. Based on incremental heating data obtained in both the UW-Madison and Gif-sur-Yvette 40Ar/39Ar laboratories, a fourth sample yields six concordant age plateaus and a weighted mean age of 105.2 ± 1.4 ka that we take as the best estimate of time since the flow erupted. Five 40Ar/39Ar incremental heating experiments on the Amsterdam Island lava yield a plateau age of 120 ± 12 ka, whereas ages from two sites in the Calderon flow are 112 ± 23 and 101 ± 14 ka, together giving a weighted mean of 104 ± 12 ka. The age of 120 ± 12 ka from Amsterdam Island, though imprecise, correlates with the Blake excursion. In contrast, the 104-105 ka age obtained from both Lipari and New Mexico indicates that these lavas record a younger period of dynamo instability, most probably associated with the post-Blake excursion. These radioisotopic ages are consistent with the astronomical ages of two paleointensity minima in the PISO-1500 global stack. Our findings indicate that the Blake and post-Blake excursions are both global features of past geodynamo behavior and support the hypothesis that Brunhes chron excursions are temporally clustered into two groups of at least a half-dozen each spanning over 220 to 30 ka and 720 to 520 ka.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 03 Geochronology; 24 Surficial Geology, Quaternary Geology; Absolute age; Amsterdam Island; Ar/Ar; Asia; Atlantic Ocean; Blake excursion; Brunhes Chron; California; Cenozoic; China; Cibola County New Mexico; Clastic sediments; Dates; Europe; Far East; France; Geochronology; Geomagnetic Instability Time Scale (GITS); Haute-Loire France; Indian Ocean Islands; Irminger Basin; Italy; Lac du Bouchet; Lava; Leg 152; Leg 162; Lipari Island; Lipari Islands; Loess; MIS 5; Maars; Marine sediments; Mono County California; Mono Lake; New Mexico; North Atlantic; ODP Site 919; ODP Site 983; ODP Site 984; Ocean Drilling Program; Quaternary; Reykjanes Ridge; Sediments; Sicily Italy; Southern Europe; United States; Upper Quaternary; Western Europe
Coordinates: N383000 N383000 E0145500 E0145500
N374730 N374730 E0773230 E0773230
N345731 N345731 W1080104 W1080104
Record ID: 2019054903
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands