Tracking the Late Jurassic apparent (or true) polar shift in U‐Pb‐dated kimberlites from cratonic North America (Superior Province of Canada)

Abstract

Different versions of a composite apparent polar wander (APW) path of variably selected global poles assembled and averaged in North American coordinates using plate reconstructions show either a smooth progression or a large ($30 ) gap in mean paleopoles in the Late Jurassic, between about 160 and 145 Ma. In an effort to further examine this issue, we sampled accessible outcrops/subcrops of kimberlites associated with high-precision U-Pb perovskite ages in the Timiskaming area of Ontario, Canada. The 154.9 6 1.1 Ma Peddie kimberlite yields a stable normal polarity magnetization that is coaxial within less than 5 of the reverse polarity magnetization of the 157.

Jurassic Monster Polar Shift Confirmed by Sequential Paleopoles From Adria, Promontory of Africa

“…Paleomagnetic data from Adria (see Channell, , for a first compilation) have been largely neglected in global‐composite APWPs, such as by Besse and Courtillot (), Kent and Irving (), and Torsvik et al (), and are therefore totally independent from them. Nevertheless, Channell et al () and Muttoni et al () have shown that Triassic and Jurassic poles from Adria map close to global‐composite APWPs, a correspondence also noted by Kent et al (). Here we show in detail that Jurassic data from Adria can be used to assess and refine the character of Jurassic APWP, especially the disputed Jurassic monster shift of Kent and Irving ().…”

“…These bioevents are the FO (=first occurrence) of C. mexicana minor and the FO of F. multicolumnatus , correlated to the MHTC12 sequence using magnetostratigraphy from the S'Adde section of Sardinia (Muttoni et al, ), and the LO (=last occurrence) of C. wiedmanni , estimated at ~156 Ma based on an Ar/Ar date (156.1 ± 0.89 Ma) on an ash layer at the top of the Rosso Ammonitico Medio at Kaberlaba (Pellenard et al, ), which is indicated. Also shown by gray bars are the age ranges of the 146.4 ± 1.4‐Ma Ithaca kimberlite pole (146Ik; Van Fossen & Kent, ), the 144 ± 5‐Ma Hinlopenstretet dikes pole (144Hi; Halvorsen, ), the 145.4 ± 1.4‐Ma Swartruggens‐Bumbeni kimberlites pole (145SB; Hargraves et al, ), and the 156.1 ± 1.6‐Ma Ontario kimberlites pole (156Ok; Kent et al, ). See text for discussion and additional references.…”

“…(1) Pole calculated by averaging poles #42–53 in Table 5 of Kent and Irving (). (2) Ontario kimberlite pole of Kent et al (). (3) The 145‐Ma pole of Kent and Irving () obtained by averaging the following items 4–6.…”

“…Kent et al () regarded the stable remanent magnetization retrieved in these kimberlites as a thermochemical magnetization associated with late stage magmatic crystallization of magnetite or magnetite growth during deuteric serpentinization, and in conjunction with the observation that this magnetite carries magnetic component directions of opposite polarity acquired at distinctly different times, they suggested that the process of magnetization acquisition may have been sufficiently long to average out geomagnetic secular variation. The 145‐Ma mean pole of Kent and Irving (; Table , entry #3) was originally defined by three igneous poles from three different continents: the Ithaca kimberlite pole 146Ik from North America (Van Fossen & Kent, ), with an updated U‐Pb perovskite age of 146.4 ± 1.4 Ma (Kent et al, ; Table , entry #4); the combined Swartruggen‐Bumbeni pole 145SB from southern Africa (Hargraves et al, ), which we assign a nominal age of 145.4 ± 1.4 Ma based on an Ar/Ar date for the Swartruggens kimberlite of 145.0 ± 0.4 (Phillips, ) and an Ar/Ar date of 145.8 ± 1.3 on the Bumbeni syenite (Hargraves et al, ; Table , entry #5); and the 144 ± 5‐Ma (K/Ar) Hinlopenstretet dikes pole 144Hi from Svalbard (Halvorsen, ; Table , entry #6). Finally, this cluster of three poles defining the reference 145‐Ma pole of Kent and Irving () is followed by a smaller return shift to the oft‐documented stillstand of poles for North America in the Cretaceous as calculated by averaging mean poles of Kent and Irving () at 60, 80, 100, and 120 Ma (Table , entry #7; Figure ).…”

Fe-Cr Mixed Binary Spinels as Accessory Magnetic Minerals in the Sudetic Ophiolitic Rocks

“…Kent et al 2015), and is interpreted by these authors in term of plate motion (referred as to the "Jurassic monster shift"). This unusually fast plate motion was previously undetected or only resulted in smooth variations around the Jurassic/Cretaceous boundary in previous composite APWPs, due to the smoothing of data intrinsic to the method of construction, or in the inclusion of lower quality Jurassic paleopoles.…”