Reconstructions of the continents using a fixed hotspot reference frame have had a tremendous impact on how we view geologic processes. The hypothesis of hotspot fixity, however, has been repeatedly challenged. We have been conducting tests of the hypothesis of hotspot fixity using paleomagnetism. In these tests, paleolatitudes are compared with the latitudes of hotspots from which they are derived. From such comparisons we derive plots of hotspot-spin axis offset versus time. These data require large-scale motion between the Atlantic, Indian and Pacific hotspot groups during the mid-Cretaceous at a velocity of approximately 30 mm/yr (Tarduno and Gee, 1995).
The rate and magnitude of this hotspot motion suggests that many concepts of plate, hotspot and true polar motion should be rethought. We are presently examining these concepts through continued paleomagnetic studies on Pacific plate sedimentary and volcanic rocks. During an Ocean Drilling Program expedition (Leg 197) to the Northwest Pacific Ocean, we collected volcanic and sedimentary samples from 3 of the Emperor Seamounts to further examine the idea that the Hawaiian hotspot may have moving in the mantle during the formation of the Emperor chain (Tarduno and Cottrell, 1997).
For a reporting of the initial results of this effort, see Motion of the Hawaiian Hotspot: A Paleomagnetic Test, Initial Reports, Proceedings of the Ocean Drilling Program, 197
For more details see recent publications of the University of Rochester's Paleomagnetics Laboratory click HERE.
Theoretical considerations and recent numerical modeling suggests that there is a relationship between geomagnetic field intensity and polarity reversal rate. However, no clear relationship is apparent in the available paleointensity data. One reason for the paucity of the paleointensity database is the low success rate.
We have developed a new approach to measure the strength of the Earth's magnetic field that uses plagioclase feldspars (Cottrell and Tarduno, 1999). These crystals, which contain magnetic inclusions that retain paleofield values, are less susceptible to alteration during paleointensity experiments than some whole rock samples (Cottrell and Tarduno, 2000).
We have been applying the method to investigate the potential relationship between intensity and the long term morphology, secular variation and reversal rate of the geomagnetic field. Our studies of the Cretaceous Superchron, based on rocks from India (Tarduno et al, 2001) and the High Canadian Arctic (Tarduno et al., 2002) suggest that the field intensity is highest when reversal rate is lowest, as suggested in some numerical models of the geodynamo. We are currently applying our method to other rock units formed during superchrons as well as to rocks formed during times of rapid reversals.
For more details see recent publications of the University of Rochester's Paleomagnetics Laboratory.
Paleomagnetic and paleointensity data of late Archean/early Proterozoic age (2.7-2.5 Ga) show many of the hallmarks of the geomagnetic field of the last 200 million years. However, we have no firm evidence for a geodynamo similar to that of modern times in the Archean (older than 2.7 billion years ago). This interval is of particular importance because Earth may have lacked a solid inner core. We are currently pursuing a laboratory and field program to collect directional and intensity data from Archean rocks, especially those of southern Africa. Determining the strength and morphology of the Archean field is important beyond the consideration of field generation. In particular, these factors help define the nature of the interaction between the early Earth's magnetosphere and the active young Sun. This interaction in turn could have influenced the development of the early Earth's atmosphere.
Large igneous provinces are massive accumulations of mafic rocks that are often associated with mantle plume activity. Because of the large volumes of new crust created, these provinces are intimately related to the tectonic development of both cratons and ocean basins in which they are found. Some provinces show a striking coincidence with extinction and/or climate events and their emplacement has been invoked as an agent of global change. One such province was emplaced in the Canadian Arctic during the Cretaceous. The principal components of the province are continental flood basalts and associated dikes and sills in preserved on Axel Heiberg Island and volcanic rocks composing the Alpha Ridge in the Amerasian Basin.
We are currently conducting a multidisciplinary study of Cretaceous volcanic rocks in the Arctic. We hope to investigate the origin of the magmatism and its relationship with Arctic tectonics, to explore whether the magmatism corresponds with climatic events and to examine its potential relationship with other Cretaceous phenomena including the anomalous volcanism seen in the Pacific Ocean and Indian Oceans (e.g. Tarduno et al., 1991). In addition, we hope to take advantage of the exposed sections as a unique opportunity to obtain high-latitude paleomagnetic data important for geomagnetic studies.
We have organized 4 expeditions to the High Canadian Arctic since 1996. Our research teams have included undergraduate students interested in field research, as well as graduate students. In 1996, we discovered a sedimentary unit overlying Cretaceous volcanics that contained abundant vertebrate fossils. These fossils indicate an unusually warm polar climate that may be related to vigorous Late Cretaceous volcanic activity (Tarduno et al., 1998).
For more details see recent publications of the University of Rochester's Paleomagnetics Laboratory.
Also, for details on our expeditions to the Arctic, click HERE.
Pelagic sediments are a potentially rich source of information on the paleointensity and paleodirection of the geomagnetic field. Deriving an accurate picture, however, depends on our ability to properly identify artifacts in the records, such as those created during diagenesis. In a detailed magnetic study of a pelagic sediment site from the western equatorial Pacific Ocean, we have found evidence for an expanded set of redox reactions involved with the decomposition of organic matter. In the magnetically stable portion of the sediment record, above the depth where sulfate reduction occurs, we have observed high frequency (100 kyr) variations in magnetic properties, that appear to be linked to paleoceanographic and paleoclimate processes. In particular, we suspect that greater organic carbon input during glacials resulted in a decrease in the grain size of the magnetic minerals (Tarduno, 1994).
We have also demonstrated that some hysteresis features linked to reduction diagenesis correspond to anomalies in directional and normalized-intensity data that might otherwise be falsely interpreted as representing geomagnetic behavior (Tarduno, 1995). We have proposed that chemical lock-in in pelagic sediments may result in a delay in remanence acquisition (Tarduno and Wilkison, 1996).
We also have applied low temperature data to understanding how the smallest magnetic fraction, superparamagnetic grains, can trace diagentic processes (Smirnov and Tarduno, 2000, 2001).
For more details see recent publications of the University of Rochester's Paleomagnetics Laboratory.
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