Abstract
SUMMARY A continental sequence of red beds and interbedded basaltic layers crops out in the Sierra Chica of Cordoba Province, Argentina (31.5°S, 64.4°W). This succession was deposited in a half-graben basin during the Early Cretaceous. We have carried out a palaeomagnetic survey on outcrops of this basin (147 sites in seven localities). From an analysis of IRM acquisition curves and detailed demagnetization behaviour, three diVerent magnetic components are identified in the volcanic rocks: components A, B and X are carried by single- or pseudo-single-domain (titano) magnetite, haematite and multidomain magnetite, respectively. Component A is interpreted as a primary compo- nent of magnetization because it passes conglomerate, contact, tilt and reversal tests. The carrier of the primary magnetization, fine-grained (titano)magnetite, is present in basalts with a high degree of deuteric oxidation. This kind of oxidation is interpreted to have occurred during cooling. Components B and X are discarded because they are interpreted as recent magnetizations. In the sedimentary rocks, haematite and magnetite are identified as the carriers of remanence. Both minerals carry the same component, which passes a reversal test. The calculated palaeomagnetic pole, based on 55 sites, is Lat. 86.0°S, Long. 75.9° E( A 95 =3.3, K=35). This palaeomagnetic pole supersedes four with anomalous positions reported in previous papers.
Highlights
The importance of apparent polar wander (APW) paths for palaeogeographic reconstructions and global tectonics is well known
Castillo et al (1991), after applying a similar procedure, obtained a mean Palaeomagnetic poles (PPs) that coincided with the present geographical pole, and suggested that South America did not experience any latitudinal movement during the Cretaceous, which contrasts with the absolute plate motion inferred from hotspot tracks (Morgan 1983)
(2) A new Early Cretaceous PP has been obtained from the virtual geomagnetic poles (VGPs) of the directions that belong to the characteristic remanent magnetization (ChRM)
Summary
A continental sequence of red beds and interbedded basaltic layers crops out in the Sierra Chica of Cordoba Province, Argentina (31.5°S, 64.4°W). This succession was deposited in a half-graben basin during the Early Cretaceous. The carrier of the primary magnetization, fine-grained (titano)magnetite, is present in basalts with a high degree of deuteric oxidation. This kind of oxidation is interpreted to have occurred during cooling. Haematite and magnetite are identified as the carriers of remanence Both minerals carry the same component, which passes a reversal test.
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