Other
Scientific paper
Feb 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985e%26psl..72..205m&link_type=abstract
Earth and Planetary Science Letters, Volume 72, Issue 2-3, p. 205-218.
Other
33
Scientific paper
Paleomagnetic samples were collected from 15 sites in the early Cretaceous Puente Piedra Formation near Lima, Peru. This formation consists of interbedded volcanic flows and marine sediments and represents the oldest known rocks of the Andean coastal province in this region. The Puente Piedra Formation is interpreted as a submarine volcanic arc assemblage which along with an overlying sequence of early Cretaceous clastic and carbonate rocks represents a terrane whose paleogeographic relationship with respect to the Peruvian miogeocline in pre-Albian time is unknown.
Moderate to high coercivities, blocking temperatures below 320°C, and diagnostic strong-field thermomagnetic behavior indicate that pyrrhotite is the dominant magnetic phase in the Puente Piedra Formation. This pyrrhotite carries a stable CRM acquired during an event of copper mineralization associated with the intrusion of the Santa Rosa super-unit of the Coastal Batholith at about 90 +/- 5 m.y. B.P. The tectonically uncorrected formation mean direction of: D = 343.2°, I = -28.6°, α95 = 3.4° is statistically concordant in inclination but discordant in declination with respect to the expected direction calculated from the 90-m.y. reference pole for cratonic South America. The observed declination indicates approximately 20° of counterclockwise rotation of the Puente Piedra rocks since about 90 m.y. This is consistent with other paleomagnetic data from a larger crustal block which may indicate modest counterclockwise rotation during the Cenozoic associated with crustal shortening and thickening in the region of the Peru-Chile deflection.
Butler Robert F.
May Steven R.
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