Remagnetization of carbonate rocks in southern Tibet: Perspectives from rock magnetic and petrographic investigations
Lippert, Peter C.
Jackson, Michael J.
Dekkers, Mark J.
van Hinsbergen, Douwe J. J.
AffiliationUniv Arizona, Dept Geosci
MetadataShow full item record
PublisherAMER GEOPHYSICAL UNION
CitationRemagnetization of carbonate rocks in southern Tibet: Perspectives from rock magnetic and petrographic investigations 2017, 122 (4):2434 Journal of Geophysical Research: Solid Earth
Rights©2017. American Geophysical Union. All Rights Reserved.
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AbstractThe latitudinal motion of the Tibetan Himalayathe northernmost continental unit of the Indian plateis a key component in testing paleogeographic reconstructions of the Indian plate before the India-Asia collision. Paleomagnetic studies of sedimentary rocks (mostly carbonate rocks) from the Tibetan Himalaya are complicated by potentially pervasive yet cryptic remagnetization. Although traditional paleomagnetic field tests reveal some of this remagnetization, secondary remanence acquired prior to folding or tilting easily escapes detection. Here we describe comprehensive rock magnetic and petrographic investigations of Jurassic to Paleocene carbonate and volcaniclastic rocks from Tibetan Himalayan strata (Tingri and Gamba areas). These units have been the focus of several key paleomagnetic studies for Greater Indian paleogeography. Our results reveal that while the dominant magnetic carrier in both carbonate and volcaniclastic rocks is magnetite, their magnetic and petrographic characteristics are distinctly different. Carbonate rocks have wasp-waisted hysteresis loops, suppressed Verwey transitions, extremely fine grain sizes (superparamagnetic), and strong frequency-dependent magnetic susceptibility. Volcaniclastic rocks exhibit pot-bellied hysteresis loops and distinct Verwey transitions. Electron microscopy reveals that magnetite grains in carbonate rocks are pseudomorphs of early diagenetic pyrite, whereas detrital magnetite is abundant and pyrite is rarely oxidized in the volcaniclastic rocks. We suggest that the volcaniclastic rocks retain a primary remanence, but oxidation of early diagenetic iron sulfide to fine-grained magnetite has likely caused widespread chemical remagnetization of the carbonate units. We recommend that thorough rock magnetic and petrographic investigations are prerequisites for paleomagnetic studies throughout southern Tibet and everywhere in general.
Note6 month embargo; First published: 12 April 2017
VersionFinal published version
SponsorsNetherlands Organization for Scientific Research (NWO) with a Rubicon grant [825.15.016]; Institute for Rock Magnetism (IRM) at the University of Minnesota; Instruments and Facilities program of NSF; ERC Starting Grant ; NWO VIDI [864.11.004]