New Early Cretaceous palaeomagnetic pole from Córdoba Province (Argentina): revision of previous studies and implications for the South American database

GEUNA, SILVANA; VIZAN, HAROLDO

GEOPHYSICAL JOURNAL INTERNATIONAL

Blackwell Publishing

Lugar: London; Año: 1998 vol. 135 p. 1085 - 1100

0956-540X

A continental sequence of red beds and interbedded basaltic layers crops out in the Sierra Chica of Córdoba Province, Argentina (31.5oS; 64.4oW). 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 7 localities). From analysis of IRM acquisition curves and detailed demagnetization behaviour, three different magnetic components are identified in the volcanic rocks: components A, B and X are carried by single or pseudosingle domain (titano) magnetite, haematite, and multidomain magnetite, respectively. Component A is interpreted as a primary component of magnetization because it passed conglomerate, contact, tilt and reversal tests. The carrier of the primary magnetization, fine grain (titano)magnetite, is present in basalts with high degree of deuteric oxidation. It is interpreted that this kind of oxidation 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. 86.0oS; Long. 75.9oE (A95= 3.3; K= 35). This palaeomagnetic pole  supersedes four with anomalous positions, reported in previous papers. Key words: South America, Argentina, Early Cretaceous, palaeomagnetism