Palaeomagnetic age of remagnetizations in Silurian dolomites, Rõstla quarry (Central Estonia)

Al ter nat ing field and ther mal de mag ne ti za tion of do lo mite sam ples from the Si lu rian (Llandovery) hor i zon tally-bed ded se quence of cen tral Es to nia re veal two sec ond ary mag ne ti za tion com po nents (A and B) both of chem i cal or i gin. A low-coercivity (de mag ne tized at £50 mT) com po nent A (D = 60.7°, I = 7.7°, a95 = 16.6°) with high dis per sion (k = 14.2), yields a palaeopole at 18.2°N and 139.5°E that points to wards the Late De vo nian — Mississipian seg ment of the Baltica APWP (Ap par ent Po lar Wan der Path). A high-coercivity com po nent B (D = 13.5°, I = 60.7°, k = 67.0, a95 = 4.7°) car ries both nor mal and re versed po lar i ties. Com par ing the palaeopole (71.1°N and 173.3°E) with the Eu ro pean APWP re veals a Cre ta ceous age. These two remagnetizations are linked to min eral as sem blages of mag ne tite and maghemite (A), and he ma tite (B) de ter mined from min er al og i cal (X-ray, SEM and op ti cal mi cros copy) and rock magnetic (ac qui si tion and ther mal de mag ne ti za tion of a 3-com po nent IRM; Lowrie-test) stud ies. The re sults sug gest that the first (A) Palaeozoic remagnetization was caused by low-tem per a ture hy dro ther mal cir cu la tion due to the in flu ence of the Cal edo nian (more likely) or Hercynian Orog eny af ter the diagenetic dolomitization of car bon ates. He ma tite, car ry ing the com po nent B, and goethite, are the lat est fer ro mag netic min er als that have pre cip i tated into the ex ist ing pore space (he ma tite) and walls of mi cro scopic frac tures (goethite) that opened to al low ac cess for ox y gen-rich flu ids dur ing the Late Mesozoic