The Santa Rosa Event; (super 40) Ar/ (super 39) Ar and paleomagneticresults from the Valles rhyolite near Jaramillo Creek, JemezMountains, New Mexico
Singer, Brad; Brown, Laurie L (2002) The Santa Rosa Event; (super 40) Ar/ (super 39) Ar and paleomagneticresults from the Valles rhyolite near Jaramillo Creek, JemezMountains, New Mexico. Earth and Planetary Science Letters, vol.197, no.1-2, pp.51-64, 30 Mar2002
| Authors | Singer, Brad; Brown, Laurie L |
|---|---|
| Year | 2002 |
| Title | The Santa Rosa Event; (super 40) Ar/ (super 39) Ar and paleomagneticresults from the Valles rhyolite near Jaramillo Creek, JemezMountains, New Mexico |
| Source | Earth and Planetary Science Letters, vol.197, no.1-2, pp.51-64, 30 Mar2002 |
| ISSN | 0012-821X |
| GeoRef | 2002-035421 |
| Keywords | absolute age; alkali feldspar; Ar/Ar; calderas; Cenozoic; dates;demagnetization; experimental studies; feldspar group; frameworksilicates; igneous rocks; Jaramillo Creek; Jaramillo Subchron; lasermethods; lower Pleistocene; magnetostratigraphy; New Mexico;paleomagnetism; Pleistocene; Quaternary; reversals; rhyolites;Sandoval County New Mexico; sanidine; Santa Rosa Event; shieldvolcanoes; silicates; time scales; United States; Valle GrandeMountains; Valles Caldera; volcanic features; volcanic rocks;volcanism; volcanoes |
| DOI | 10.1016/S0012-821X(01)00598-2 |
Abstract
The Jaramillo Event was originally defined by Doell and Dalrymple in1966 on the basis of K-Ar ages from sanidine in the normally,transitionally and reversely magnetized rhyolite domes named Cerro delAbrigo, Cerro Santa Rosa I and Cerro Santa Rosa II, respectively, thaterupted following collapse of the archetypal Valles Caldera, NewMexico. We have collected new paleomagnetic data from the three domesand new (super 40) Ar/ (super 39) Ar laser fusion and furnaceincremental heating experiments on sanidine crystals from the CerroSanta Rosa I rhyolite. Step-wise alternating field and thermaldemagnetization techniques applied to 52 samples from seven sitesindicate that the original paleomagnetic results of Doell andDalrymple [Science 152 (1966) 1060-1061] are valid. Cerro del Abrigois normally magnetized, whereas the Santa Rosa I dome is transitionalwith an inclination of -63 degrees toward the east and the Santa RosaII dome is of reversed polarity. Twenty-five laser fusion experimentson sanidine crystals from the the Cerro Santa Rosa I dome, togetherwith the saddle-shaped spectrum obtained by incrementally heating thesanidine in a furnace reveal that this rhyolite contained a small butsignificant component of excess argon prior to eruption. Our preferredage of 936+ or -8 ka (+ or -2sigma ) for the Santa Rosa I rhyolite isbased on the concordant laser fusion isochron and incremental heatingplateau ages. This age is significantly older than was inferred on thebasis of earlier laser fusion (super 40) Ar/ (super 39) Ar resultsthat suggested a trapped component characterized by a (super 40) Ar/(super 36) Ar ratio lower than the atmospheric value of 295.5. Our newage distinguishes the Santa Rosa I dome by 65 kyr from the terminationof the Jaramillo normal subchron 1001+ or -10 ka and by 37 kyr frombasaltic lavas at Haleakala and Tahiti, which record the KamikatsuraEvent 899+ or -6 ka. Moreover, this determination is a factor of threemore precise than the best previous estimate for a proposedgeomagnetic event in this time period. The Cerro Santa Rosa I rhyolitedome, once intimately linked with the end of the Jaramillo Event andthe acceptance of plate tectonic theory, now defines a highly resolvedfeature, the Santa Rosa Event, in a terrestrial geomagnetic reversaltime scale that is consistent with the global record of magnetic fieldintensity from marine sediments.