A possible mid-Holocene age of the Carrizozo Malpais from paleomagnetics using secular variation magnetostratigraphy
Stephen L. Salyards
To place constraints on the age of the malpais northwest of Carrizozo, New Mexico, 14 samples were collected from two different sites on the eastern edge of the flow. One site is located on the surface of a small lobe of basalt on the eastern margin. The second site is located about 150 m west of the eastern limit of the flows in the interior of a filled lava tube. Both groups of samples held strong paleomagnetic signatures; however, the samples on the margin of the flow exhibited differing alternating field and thermal demagnetization behavior. Demagnetization by alternating field produced a strong single-component demagnetization path while thermal demagnetization shows multi-component behavior. Similar behavior was demonstrated by the samples from the interior of the flow, except that the multi-component behavior of the thermal samples was less pronounced. This differing behavior is indicative of magnetic overprinting. In the data analysis a least-squares line was fit to the alternating field samples while both lines and planes were fit to the thermal samples. The results showed good clustering of all lines within a group and a well-defined girdle of poles to planes. The directions of all groups are steeply inclined and significantly east of the dipole field for this site, making them unique. The archaeomagnetic secular variation reference curve for the southwestern United States contains no virtual geomagnetic pole corresponding to these directions constraining the flow to older than 580 A.D. We prefer an approximate age of approximately 5000 years b.p. based upon the Fish Lake, Oregon, secular variation record, an age corroborated by a preliminary 16Cl date on the flow.
- Salyards, Stephen L., 1991, A possible mid-Holocene age of the Carrizozo Malpais from paleomagnetics using secular variation magnetostratigraphy, in: Geology of the Sierra Blanca, Sacramento and Capitan Ranges, New Mexico, Barker, James M.; Kues, Barry S.; Austin, George S.; Lucas, Spencer, G., New Mexico Geological Society, Guidebook, 42nd Field Conference, pp. 153-157.