Is the Teisseyre‐Tornquist Zone an ancient plate boundary of Baltica?

Abstract

The Teisseyre-Tornquist Zone (TTZ) is generally regarded as a fossil plate boundary in Europe that extends 2000 km from the Baltic Sea to the Black Sea. We used an integrated approach merging potential fields and seismic data to explore crustal architecture across the TTZ in central Poland. The aim of the study was to test whether the TTZ coincides with an early Paleozoic (Caledonian) suture formed through the closure of the Tornquist Ocean along the SW Baltica margin. The suture is presumed to separate the East European Craton (EEC) from the Paleozoic terranes of Western Europe. Two seismic reflection lines from the PolandSPAN ™ experiment were used to image the deep structure at the SW margin of the EEC. Lines PL-5300 and PL-5400 run NE-SW in central and northern Poland, respectively. The seismic interpretation down to top of basement was integrated with 2-D gravity and magnetic modeling to highlight the structure of the deep crust. Both the gravity and magnetic models show a suture that welds together two blocks at the base of crust. However, top of basement above the suture dips uniformly to the SW and is overlain by undisturbed lower Paleozoic and younger sediments. By implication, the suture must have developed in the Precambrian and both crustal blocks amalgamated belong to the EEC. Consequently, the Caledonian suture, formed by the closure of the Tornquist Ocean between Avalonia and Baltica, must be located farther southwest beneath thick upper Paleozoic and Mesozoic sediments.

Basement structure of the Paleozoic Platform in Poland

“…For ex am ple, Berthelsen (1998) ar gued that the zone is in fact an intraplate pseudosuture of Car bon if er ous to Early Paleocene age, within a con tin u ous EEP base ment ("Baltica crust") ex tend ing far ther to the SW. In the same vein, Mazur et al (2015) while main tain ing pre vi ous ideas of con tin uous crys tal line EEP crust ex tend ing far to the west (see the section "Pre vi ous con cepts"), in ter preted the TTZ as an intracratonic su ture be tween two Pre cam brian blocks of dif ferent crustal thick ness. Con se quently, the con tin u ous Lower Paleo zoic cover was in ter preted to ex tend far ther south-west beyond the TTZ, above the grad u ally deep en ing base ment top.…”

“…This pro file pro vided the first detailed ob ser va tions on the base ment top and in ter nal struc ture of the lower crust be yond the EEP in Po land. Re cently published re sults of the PolandSPAN Pro ject served as an ad ditional source of in for ma tion (Mazur et al, 2015(Mazur et al, , 2016bsee Fig. 1B for lo ca tion of the pro files).…”

“…Key new data with far-reach ing con se quences for the ge ol ogy of the Pa leo zoic Plat form were re cently sup plied by the deep re flec tion seis mic pro file POLCRUST-01 cross ing the TTZ in SE Po land (Malinowski et al, 2013Narkiewicz et al, 2015). Re cently pub lished re sults of the regional re flec tion seis mic PolandSPAN Pro ject also pro vide a new source of data on the deeper struc ture of the SW mar gin of the EEP (Mazur et al, 2015(Mazur et al, , 2016b.…”

“…In a re cent pa per Mazur et al (2015) re turned to the pre vious idea of the con tin u ous EEP base ment ex tend ing as far as the Elbe Line in the south-west ( Fig. 1A; e.g., Berthelsen, 1998;Bayer et al, 2002).…”

“…The main ob jec tions may be sum ma rized as fol lows: (1) Mazur et al (2015) did not doc u ment the phys i cal ex is tence of a crustal keel and the pres ence of an over ly ing Lower Pa leo zoic plat form cover, (2) the po ten tial field anom aly pat terns mark ing the sup posed keel/su ture are in con sis tent, thus ap par ently re lated to dif fer ent re gional subsurface units, (3) no con sid er ation was given to the ear lier WARR re sults and their in ter pre ta tions (i.a., Guterch and Grad, 2006;Puziewicz, 2006), (4) there was an ap par ent con tra dic tion between the con cept of a grad u ally deep ened base ment top across the TTZ and the ex is tence of the first-or der hor i zon tal mag netic gra di ent con nected with this struc ture. Pom er a nian Block 1.7-3.7 Ediacaran?…”