Magnetic properties of a suite of variably serpentinized peridotites from the Dongbo ophiolite, SW Tibet (China), have been investigated to determine the magnetic signatures of suture zones. The degree of serpentinization (S) for these peridotites is mainly in the range of S < 60%. Petrography, mineral chemistry, and thermomagnetic analyses reveal that magnetite occurring in the interior of various serpentine veins is the predominant magnetic phase. Magnetic hysteresis and first-order reversal curve diagrams suggest that the magnetite is mixture of interacting single-domain, and pseudo-single-domain and/or multidomain particles. Superparamagnetic magnetite occurs in the S = 40–60% serpentinized but weakly magnetic dunites. Overall, the magnetite content and magnetic susceptibility increase consistently from ~0 to 20% of serpentinization and then decrease from S = 30 to 60%. Peak magnetite abundance is at S~25% (density, ~3.1 ± 0.05 g cm–3) and may suggest localized enrichment of fluids. The low magnetite abundance in dunite results from low-temperature serpentinization. Finally, strong intensities of magnetization (1–10 Am–1) reside in the S > 60% and S = 20–30% serpentinized peridotites, indicating that peridotites with such degrees of serpentinization contribute to the aeromagnetic anomalies within the Yarlung-Zangbo suture zone in south Tibet.
Bibliographical noteFunding Information:
This work was supported by the China Postdoctoral Science Foundation (2015M572218), the National Science Foundation of China (41504053, 41520104003, and 41374094), and the China Geological Survey (12120115027201). This is IRM contri bution 1701. The IRM is supported by the Instruments and Facilities Program of the NSF Division of Earth Science. Mike Jackson and Dario Bilardello from IRM offered generous help in the mag netic measurements. Constructive comments from Mark J. Dekkers (Associate Editor) and two anonymous reviewers have improved the quality of the manuscript. Data presented in this paper can be accessed in the online version at http://dx.doi.org/10.1002/ 2017JB014241.
- rock magnetism
- suture zone