鄂尔多斯盆地南缘上奥陶统赵老峪组岩石磁学研究OA北大核心CSTPCD

[Objective]Palaeomagnetic methods can be used to quantitatively constrain the Early Palaeozoic palaeo-position of the North China Block(NCB),which provides a crucial scientific basis for researching the evo-lution of the Proto-Tethyan Orogeny and the affinity of the NCB for Gondwana.However,the NCB has undergone considerable tectonic activity since the Early Palaeozoic,and the Ordos Basin in the western part of the NCB is rich in hydrocarbon resources.Late tectonic activity and the migration of hydrocarbon resources may have caused remag-netization of Early Palaeozoic strata.[Methods]Thus,in this paper,to determine the main magnetic minerals in various rocks and their ability to record the primary remanent magnetization,we carry out a series of detailed pe-trography,rock magnetism and stepwise demagnetization experiments on the limestone and tuff samples of the Upper Ordovician Zhaolaoyu Formation in the Fuping area of the southern Ordos Basin,including optical microscope iden-tification,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),saturated isothermal rem-anent magnetization(SIRM)acquisition curve,three-axis isothermal thermal demagnetization test,κ-T curve test,hysteresis loop experiment,first-order reversal curve(FORC),and thermal demagnetization and hybrid(TD+AF)demagnetization.[Results]The results indicate that the main magnetic minerals in the limestone and tuff samples are magnetite,pyrrhotite and/or greigite,and some samples also contain a tiny quantity of haematite with impurities and goethite.Mineral particles possess single domains(SDs)as well as multiple domains(MDs)within their mag-netic domains.Combining petrographic and demagnetization data,this paper suggests that the main magnetic min-erals in the samples are likely secondary minerals associated with later fluid alteration(maturation and migration of organic matter).[Conclusion]The remanent magnetic signals conveyed by these rocks cannot be directly used to constrain the Early Palaeozoic palaeoposition of the NCB but may be used to constrain hydrocarbon migration and accumulation in the Lower Palaeozoic strata of the southern Ordos Basin.