Magnetostratigraphic Study Of U1518 Station In The Northern Margin Of Hikurangi Subduction Belt,New Zealand

The International Ocean Discovery Program?IODP?375 voyage is dedicated to exploring the slow-slip events of earthquakes in the Hikurangi subduction zone in eastern North Island,New Zealand.U1518 is located near the front fault of accretion wedge in Hikurang subduction zone.It is very challenging to establish its magnetic stratigraphic framework.On the basis of SRM data of ship survey for drilling cores,SRM data are processed and interpreted by Puffinplot software system.The best line segment fitted by Kirshcvink principal component analysis?PCA?is used to determine the polarity of characteristic remanence vector.The geomagnetic polarity of123¹75 m,198²60 m and 260³04 m strata below the seabed is mainly studied.Based on the data of lithostratigraphy and biostratigraphy,the magnetic stratigraphic sequence and chronological framework of U1518 station are established.After 16.62 days,four boreholes were drilled at U1518 station:U1518E,F,G and H boreholes,and paleomagnetic samples?Pmag?were collected according to core orientation rules.According to the core judgement of U1518,it is divided into three lithostratigraphic units:Unit I,Unit II and Unit III.The overall characteristics of stratum structure are silty clay rock,siltstone and fine siltstone interbedding.In the field of magnetic formation,there are four types of residual magnetism in core samples:residual magnetism while drilling,viscous residual magnetism,sedimentary characteristic residual magnetism and rotary residual magnetism.Based on the analysis of the test data of magnetic susceptibility anisotropy,it is found that there are two distinct coercive components in the core,one is titanomagnetite,the other is autogenous glue pyrite.Based on SRM partial alternating demagnetization data and Pmag sample system demagnetization and stepwise thermal demagnetization results,the rock magnetic properties and geological significance of drilling cores are studied.Puffinplot software system and Kirshcvink principal component analysis?PCA?are used to determine the geomagnetic polarity of the study interval,and the framework of magnetic stratigraphy and chronology is established:The strata of 0-123 meters are composed of a single positive polarity zone and a cloth positive polarity period?C1_n?;123¹98.325 meters are composed of a single negative polarity zone and a Songshan negative polarity period(C1_r.1_r);198.325³04 meters are composed of a mixed polarity zone with positive polarity as its main component in the upper part and a single positive polarity zone as a whole in the lower part,and a Jaramilo positive polarity subzone(C1_r.1_n);304³24.35 meters are composed of a single positive polarity zone.Fault zone rocks,polarity is uncertain;324.35⁴97.4 m section strata,the overall single positive polarity zone,cloth positive polarity period?C1_n?.This study provides reliable chronological constraints for the study of volcanic climate change and paleo-oceanic evolution in the Hikurangi subduction zone,and has a certain reference value for the study of magnetic stratigraphy in the active tectonic zone.