An Historical Perspective of the Early Palaeozoic APWP of Gondwana: New Results from the Early Ordovician Black Hill Norite, South Australia

The contribution of geochronology to understanding the Paleozoic geological history of Australia

“…Reviewing the history of the Australian apparent polar wander curve for the Early Paleozoic, Schmidt et al (1993) lamented the lack of reliable poles from the Gondwana continents. While some poles suggested a small separation between Gondwana and Laurentia, others suggested the presence of a wide ocean.…”

The remote determination of magnetic remanence

“…Regions of the magnetic data that were adversely influenced by cross cutting intrusions were eliminated from the data prior to inversion. Q values from palaeomagnetic measurements exceed 2 and when we use the average estimate of magnetic susceptibility from Schmidt et al (1993) of 0.05 SI, our Q estimate from inversion of the data over the whole intrusion is approximately 5. This is consistent with the very close match between the measured remanent magnetic direction and resultant magnetization direction.…”

“…Schmidt et al, 1993 Pmag 1 223 9 Schmidt et al, 1993 Pmag 2 231 20 This study Rem inv 230 18 Note: "MM" refers to the magnetic moment method, "Pmag" refers to laboratory palaeomagnetic measurements of rock samples, "Res inv" refers to resultant magnetization vector inversion and "Rem inv" refers to the remanent vector directions derived from inversion using the average laboratory value for magnetic susceptibility. Schmidt et al (1993) used their laboratory measurements to establish a palaeopole location estimate for the Black Hill Norite with an Early Ordovician age of 487 ± 5 million years (Turner, 1990). Figure 5 shows an image of the total magnetic intensity for a segment of the Brewarrina aeromagnetic survey over the southern part of the Thompson Fold Belt (NSW, latitude, 29.84, longitude 147.00).…”

Recovery of Resultant Magnetization Vectors from Magnetic Anomalies

“…Paleomagnetic studies of the BHN have found magnetic susceptibilies of 0.02-0.05 SI, Q=2.1, and a recovered NRM direction of declination 221.2° and inclination 7.6° . Schmidt et al (1993) also found a steeper high temperature NRM component possibly attributed to secular variations. No outcropping rock is available to sample the CMP.…”