Precise ages of the Reunion event and Huckleberry Ridge excursion; episodic clustering of geomagnetic instabilities and the dynamics of flow within the outer core

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doi: 10.1016/j.epsl.2014.08.011
Author(s): Singer, Brad S.; Jicha, Brian R.; Condon, Daniel J.; Macho, Alexandra S.; Hoffman, Kenneth A.; Dierkhising, Joseph; Brown, Maxwell C.; Feinberg, Joshua M.; Kidane, Tesfaye
Author Affiliation(s): Primary:
University of Wisconsin, Madison, Department of Geoscience, Madison, WI, United States
Other:
British Geological Survey, United Kingdom
California Polytechnic State University, United States
Deutsches GeoForschungsZentrum, Germany
University of Minnesota, United States
Addis Ababa University, Ethiopia
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, Vol.405, p.25-38. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Includes appendices. 62 refs.; illus., incl. 2 tables
Summary: The Réunion event is one of the earliest recognized periods of normal polarity within the reversed Matuyama chron. Named for the site at which it was first discovered on Reunion Island, it has since purportedly been found globally in both volcanic rocks and sediments, and thus has become a key chronostratigraphic marker. However, geochronologic results from several locations thought to have recorded this event have caused considerable confusion regarding not only its age and duration, but also the number of Reunion events. New 40Ar/39Ar ages from eight Reunion Island lavas in three distinct sections are indistinguishable from one another, thereby placing the event at 2.200±0.007/0.010 Ma (±3σ analytical/total uncertainty, note this format is used throughout the paper). The paleomagnetic behavior recorded at two of the island sites shows that the opposite (normal) polarity was reached and sustained for a period during which several lava flows were erupted. Whether this can be classified as a very short subchron bounded by a rapid set of back-to-back reversals, or as a special case of a geomagnetic excursion, is unclear. Hence, we choose to continue labeling the dynamo activity recorded by these Reunion Island lavas as an "event". This event preceded a ∼38 kyr period of normal polarity that we name the Feni subchron after its locality of discovery at ODP site 981. The Feni subchron was succeeded by the Huckleberry Ridge excursion for which 40Ar/39Ar sanidine and U-Pb zircon ages of 2.077±0.001/0.003 Ma and 2.084±0.012/0.013 Ma, respectively, from member B of the Huckleberry Ridge tuff in Idaho, are in agreement. These findings suggest that the full normal polarity recorded on Reunion Island is a singular brief period of unstable field behavior at the onset of a ∼125 kyr bundling of dynamo instabilities from 2.20 to 2.07 Ma. Disturbances to the axial dipole component of earth's magnetic field during this period, and by analogy similar periods of temporally-clustered excursions during the early and late portions of the Brunhes chron, may reflect disruptions to convective flow arising from parcels of material introduced into the outer core from either the inner-core or core-mantle boundaries; a proposition that might be tested by future numerical dynamo simulations. Abstract Copyright (2014) Elsevier, B.V.
Year of Publication: 2014
Research Program: ODP Ocean Drilling Program
Key Words: 03 Geochronology; 18 Geophysics, Solid-Earth; Absolute age; Africa; Ar/Ar; Argentina; Atlantic Ocean; Brunhes Chron; Cenozoic; Cerro del Fraile; Chronostratigraphy; Core; Dates; Dynamos; East Africa; Ethiopia; Feni Drift; Geochronology; Huckleberry Ridge Tuff; Igneous rocks; Indian Ocean Islands; Lake Gamarri; Leg 162; Mascarene Islands; Matuyama Chron; North Atlantic; Numerical models; ODP Site 981; Ocean Drilling Program; Outer core; Paleomagnetism; Pleistocene; Quaternary; Reunion; Rockall Bank; South America; Temporal distribution; Upper Cenozoic; Upper Quaternary; Volcanic rocks
Coordinates: N552838 N552838 W0143903 W0143903
N113214 N113214 E0414007 E0414007
S503200 S503200 W0723900 W0723900
S212500 S205000 E0560000 E0550000
Record ID: 2014089570
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands