PALEOMAGNETISM OF EARLY PALEOZOIC ROCKS OF THE DE LONG ARCHIPELAGO AND TECTONICS OF THE NEW SIBERIAN ISLANDS TERRANE Metelkin D.V., Chernova A.I, Trofimuk Institute of Petroleum Geology and Geophysics SB RAS Matushkin N.Yu., Vernikovsky V.A. [email protected] Novosibirsk State University Novosibirsk, Russia Paleotectonic reconstructions for 520-440 Ma Abstract 520 Ma Jeannette Island North NSI South The De Long archipelago is located to the north of the Anjou archipelago as a part of a Paleoasian30 O ocean hemisphere hemisphere 30 O large group between the Laptev Sea Bennett Island and Henrietta Island, the New Siberian OM Paleoasian ocean . Islands and consists of Jeannette Island– and the East Siberian Sea tTwhose tectonic history was independent of other, hese islands have been shown CH CH Siberia Siberia o be part of a single continental terrane Paleomagnetic and precise geological data for the De Long equator equator De Long archipelago were. continental masses at least since the Ordovician special inter Archipelago nnational field trips to the De Long Islands could be organized and geological???? Only i NSI OM Laurentia . absent until recently, geochronological and paleomagnetic studies were carried out-isot Kara Laurentia Kara .ope Baltica 30 30 O O Iapetus ocean Baltica aOThe age of these dikes is more. sedimentary sequence intruded by mafic dikes w Svalbard New Siberian Islands Svalbard s described-n Jeannette Island a volcanic Ar and paleomagnetic investigations of the/ a Iapetus ocean s evidenced by the results of our Ar, Ma48? close to , likely Early Ordovician there are wid 60 O 60 eespread, On Bennett Island. dolerites as well as the result from detrital zircons in th Bennett Island O Gondwana host rocks published before Paleomagnetic results from these rocks characterize the pale Gondwana ogeographic. Ordovician mainly terrigenous rocks-Cambrian although there is no evi ndence for the primary origin of, Ma5?? Ma and perhaps at 465 position of the De Lo g archipelago at A. sedimentary section was investigated-On Henrietta Island the Early 480 Ma Cambrian volcanic. magnetization for the latter Adding to our previous paleomagnet ic. Ar results/ Ma was obtained and confirmed by new Ar5?? paleomagnetic pole for data NSI for the Anjou archipelago the extended variant of the apparent polar wander path for the OM 30 30 O New Siberian Island terrane was degrees4? The established paleolatitudes define its O Paleoasian ocean Paleoasian ocean location in the equatorial and subtropical zone no higher than . created Because there are CH u no good confirmations for true polarity and related geographic hemisphere we. d Henrietta Island CH ring the Early Paleozoic But both these solutions demonstrate a very close paleogeographi equator Siberia Siberia c position. present two possibilities for tectonic reconstruction between the New Siberian Laurentia equator Laurentia .Island and the Siberian continent The study was supported by Ministry of Education and Science of the Russian Federation Iapetus ocean OM Kara Kara (5????4????7grant No ), RSF (grant ?4-?7-?????No ), RFBR (?5-?5-??4?8grant No ). Iapetus ocean NSI 30 O Svalbard Svalbard 30 O Rheic ocean Rheic ocean Geological maps of Bennett, Henrietta and Jeannette158 IslandsO00’ E Baltica O O O Table. Mean paleomagnetic directions, paleomagnetic poles coordinates and paleolatitudes based on 149 00' E 149 20’ 156O26’ E 156 39’ E. Baltica 60 O QIV 2 km paleomagnetic study of Early Paleozoic archipelagos Anjou and De Long, which used for the NSI 60 ˆ 1 Jeannette Is. O Polar st. Dyunbar cape N Porphyric diorite and QIV Henrietta Is. APWP Bennett Is. K1 Pz tg subvolcanic basalts O 1 km 2-3 45 1-2 2 O Pavel Keppen Objects, Geographic coordinates Stratigraphic coordinates Paleomagnetic poles Gondwana Gondwana 75 43' K1 Unexplored area Plat K Basalts ? n/N N 1 bay Bennetta cape age O O D I k a95 D I k a95 PLat PLong A95 2 2 3 O 65 1-2 Tuffaceous gravelites, Q 60 Koteny Is., limestones 43/45 440 Ma O IV K 1 208.3 81.5 87.0 9.9 272.0 53.9 558.5 3.9 33.7 55.7 5.1 34.4 60 1 4 50 sandstones 13NS01 36 (4) 11NS10 76O47’ N 440 Ma 13NS02 34 11NS11 70 K1 25 Tuffaceous siltstones Paleopacific 41 Bennett Is., sandstones 25/33 K Pz2-3bz 72 Paleopacific 11NS12 1 5 13NS03 2 298.5 54.1 109.3 11.9 307.7 57.4 178.4 9.3 45.5 31.9 11.0 38.0 Zeeberg Glacier 5 45 465 Ma (3) 30 Quartz and polymictic 35 40 NSI O K Pz2-3tg 31 1 Q 42 30 O 30 IV 6 17 sandstones, shales 1 km Kotelny Is., dolomites 23/25 3 278.3 77.5 25.7 51.4 315.6 59.1 414.0 12.3 48.9 13.8 18.1 39.9 (2) O 13NS12 18 475 Ma 75 40' O 13NS04 dolerite dykes OM 13NS10 1-2 Pz kp unit 1, volcanogenic-clastic turbidites, Chernyshev 7 1 13NS05 dolerite dikes 13NS11 sandstones, gravelstones, tuffs; Jeannette Is., dolerites, 39/45 36.5 CH pen. Pz bz Pz1ta 4 308.7 44.8 55.5 16.7 344.4 56.0 468.7 5.7 49.2 357.4 5.9 CH 1 13NS07 480 Ma (3) Siberia 8 13NS08 thrusts faults: Siberia O2 ˆ QIV 13NS06 unit 2, mainly tuff breccias; Pz ta N of uncertain kinematics (a), Henrietta Is., sandstones, ˆ 18 2-3 b O2 K Pz2-3tg 56/65 1 a c upthrow-thrust kinematics (b) 5 tuffs, basalts 294.5 25.4 19.0 14.2 295.5 34.0 282.0 3.6 23.7 45.7 3.2 18.6 10 paleomagnetic (6) Sophia cape unit 3, volcanogenicclastic 520 Ma Paleoasian ocean PaleoasianKazakhstan ocean sample sites inferred faults (c); Kazakhstan 11 6 8 turbidites and tuff breccias; Kara equator 1 – Cambrian deposits; 2–3 – Ordovician deposits; 4 – Cretaceous 3 Kara equator 70 50 Pz kp 12 Bennett Is., sandstones 18/22 deposits; 5 – Cretaceous basaltic covers; 6 – Paleogene- 1 13NS09 unit 4, coarse-grained volcanogenic paleomagnetic 6 (2) 247.8 46.5 184.3 18.5 249.2 37.0 265.1 15.4 15.5 83.6 18.0 20.6 O 530 Ma Quaternary deposits; 7 – fauna findings; 8 – paleomagnetic 156 39’ E -clastic turbidites; sample sites Svalbard sampling sites. Svalbard Laurentia OM Paleomagnetic study results Laurentia Uralic ocean NSI Uralic ocean Site 13NS07 APWP for NSI terrane Baltica Site 13NS04 Site 13NS01 Baltica O Site 11NS11 N,UP N UP N UP N N,N 30 O 30 N Upper N Upper Upper N Upper Lower Lower Iapetus ocean Lower Lower 630 °C 120 mT Mean paleomagnetic directions NRM ChRM 1213 600°C New Siberian Islands (NSI) Rheic ocean N Rheic ocean NRM NRM Upper NRM ChRM Lower 400 °Ñ ChRM 60 O [Vernikovsky et al., 2013, Middle Lower-Middle 60 Lower NRM Metelkin et al., 2016] Laurentia Cambrian O Ordovician Upper [Cocks, Torsvik, 2011] 250 Gondwana Gondwana Sample 11NS141 E,E Sample 13NS054 E 250 630 °C 360°Ñ 475 270 Upper Ordovician- Bazalt E Sandstone 400 °Ñ 480 270 Lower Silurian 465 290 Mmax= 55.6 mA/m Sample 13NS085b Mmax=0.24 ìA/ì 460 °C E Mmax= 266 mA/m Mmax=0.69 ìA/ì Paleotectonic reconstruction in which two possible scenarios of NSI terrane position in the Early Paleozoic are presented: on top - N-scenario 1 1 1 1 Lower Cambrian Tuff E Sample 13NS011 440 310 120 mT E,UP for nothern hemisphere, on bottom - S-scenario for southern hemisphere. NSI - New Siberian Islands terrane, OM- Omulevka terrane, CH - 600°C Tilt Dolerite 320 440 corrected 9 mT 370 Chukchi-Alaska terrane. 180 °C [Zhdanova et al., 2016] 470 460 350 N-scenario supposes the normal polarity of geomagnetic field while rocks forming and placing the NSI terrane in the northen hemisphere. Such M/Mmax NSI 520 M/Mmax M/Mmax NRM M/Mmax 490 ChRM 405 Sample 13NS085b 530 400 an option is advantageous because of the minimum horizontal displacements of the terrane resulting from the analysis of the entire set of NRM 515 Equator NRM 430 400 °Ñ 0 0 paleomagnetic data. At the other hand, in this case in the Early Cambrian it should be over a significant distance from Verkhoyansk margin of 0 60 120 mT 0 200 0 315 630 °C 0 300 600 °C [Chernova et al., 2017] 440 530 Baltica [Torsvik et al., 2012] Siberia with which there was a obvious biogeographic link at that time. We assume that this space could be occupied by Omulevka and probably Upper Site 13NS11 W,UP Upper N N UP Upper Site 13NS09 N UP N Site 13NS02 Upper N Preliminary, not published results 450 Lower Site 13NS05 Lower Lower N,N Lower Chukchi-Alaska continental terranes which enabled the fauna to migrate along the shelf. In the Ordovician it is supposed the disintegration this (Bennett Islands Cambrian sandstones) 460 NRM 470 system and further convergence with the Siberia. The downside of this model is that such NSI position is to far from Baltic which is supposed as NRM 540 500 NRM 500 a main provenance area of detrital zircons (Ershova et al., 2016) and this fact should be sought for another explanation. ChRM 600°C Siberia 1 Poles for De Long Islands [Cocks,Torsvik, 2007] 520 The second variant (S-scenario) assumes a more typical for the early Paleozoic reverse polarity of the geomagnetic field and the southern NRM NRM Poles for Anjou Islands 520 80 mT position of the NSI terrane.