Tectonic models for Borneo's Cenozoic evolution differ in several aspects, particularly in the extent to which they include paleomagnetic data suggestive of strong counterclockwise rotation between 30 and 10 Ma. Key areas are undersampled. We present the results of a paleomagnetic study of Eocene to Early Miocene sandstones from northwest Sabah, principally from the Crocker Formation. We obtained reliable site means from 11 locations along a 250 km northeast-southwest transect using thermal demagnetization to isolate characteristic remanent magnetization (ChRM) directions. The Crocker Formation sandstones are pervasively remagnetized; pyrrhotite dominates the ChRM signal. Locations can be grouped into different domains on the basis of the relative sense of rotation about a vertical axis. Mean ChRM directions for seven locations between Kota Kinabalu and Keningau (declination, dec 12°-19°; inclination, inc-22°-23°) indicate minor clockwise rotation and modest tilting, whereas two locations near Tenom (dec 321°-345°, inc-6°-24°) record counterclockwise rotation and modest tilting. Although we cannot precisely date the age of remagnetization, the results of fold tests from 4 locations, interpreted within the regional structural framework, strongly indicate that remagnetization occurred between 35 and 15 Ma, the waning stages of the Sarawak orogeny to an early phase of the Sabah orogeny. Our results pose serious diffi culties for current tectonic models in which Borneo rotates 50° counterclockwise as a rigid block between 30 and 10 Ma. With respect to prior paleomagnetic studies, we suspect that an early episode of strong regional counterclockwise rotation (before 35 Ma) was over-printed not only by differential clockwise rotation of crustal blocks during opening of the South China Sea (32-23 Ma), but also locally by a younger (after 10 Ma) counterclockwise rotation.

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An integrated palaeomagnetic, geochemical and petrographic study was conducted on two folds in the Front Range of the Southern Canadian Cordillera in order to better understand the timing and origin of chemical remanent magnetizations (CRMs) relative to orogenesis. The folds are contained within Mississippian carbonates (330–335 Ma) which contain a pervasive pre-tilting to early syn-tilting Early Cretaceous, high-temperature CRM residing in magnetite. An intermediate-temperature CRM is a late syn-tilting to post-tilting, possibly Tertiary remagnetization, residing in pyrrhotite. A fluid conduit test (FCT) conducted on bedding-parallel veins shows that they are associated with the magnetite CRM, whereas late-stage tensile veins show a relationship to a pyrrhotite CRM. Elevated 87Sr /86Sr data indicate alteration by fluids with a radiogenic signature; along with the FCT results, these data are consistent with the interpretation that the magnetite CRM formed as a result of hydrocarbons and/or evolved basinal fluids that migrated ahead of the deformation front. Based on the presence of sulphur-enriched bitumen, barite and sphalerite, common by-products of thermal sulphate reduction (TSR), the pyrrhotite CRM is interpreted to be the result of late-stage TSR caused by warm basement fluids which moved along faults and fractures.

Palaeomagnetism of 273 specimens from 24 sites isolated a well‐defined characteristic remanent magnetization (ChRM) direction on AF and thermal demagnetization in seven host carbonate and 14 ore mineralization sites from the Galmoy Zn–Pb deposit. Thermal decay and saturation remanence data show that the ChRM is carried dominantly by single domain magnetite. Palaeomagnetic field stability tests indicate a post‐brecciation and post‐folding ChRM. The ChRM directions from the host rock and mineralized sites are indistinguishable at 95% confidence and give a palaeopole at 41.5°S, 8.4°W (dp = 1.5°, dm = 3.0°) with an age of 290 ± 9 Ma on the Laurentian apparent polar wander path. This Early Permian age at Galmoy records Variscan orogenesis and suggests an epigenetic model in which mineralization occurred during cooling from the regional Variscan thermal episode.