Riccardo Callegari: The timing of Iapetus opening and its implicationsfor understanding the break-up of Rodinia andevolution of Baltica: Insight from SwedishCaledonides and central Poland

Abstract

Plate tectonics as a simple concept can be summarized as follows: a supercontinent breaks up and different portions of it are driven apart from one another forming new oceans. Eventually, the continents will merge again closing the ocean between them. This cycle is called the “Wilson Cycle”. While the basic concept of a Wilson Cycle is well accepted, the specifics of the timing and dynamics of continental break up often remain mysterious. This PhD project aims to determine precisely when the Iapetus Ocean formed following the break-up of the ancient continent Rodinia. Additionally, this PhD thesis investigates the evolution of Baltica, one of the continents formed by the separation of Rodinia. 

In order to achieve these goals, several methods are applied to rocks collected from different localities. Metaigneous rocks were collected from the northern part of the Swedish Caledonides and constitute the samples for Chapter 1 and 2. These rocks are related to igneous activity associated with continental break-up and opening of the Iapetus Ocean and were subsequently metamorphosed during the later stage of the Wilson Cycle, when subduction and collision of Baltica with Laurentia formed the Caledonian Orogeny. Chapter 3 investigates (meta)sedimentary rocks from the Holy Cross Mts. in southwestern Poland. They record evidence of the break-up and rifting, because they represent a portion of the paleo-southwestern margin of Baltica and record information about Baltica’s evolution through time.

In terms of analytical techniques, the PhD project started with classical petrological investigation using a microscope, chemical characterization of minerals using electron microprobe (EMP), whole-rock major and trace element geochemistry, geochronology (U-Pb monazite and zircon and 39Ar/40Ar white mica), conventional and trace element geothermobarometry and phase equilibria modelling.

The new data collected in this PhD project provide new insights into the Neoproterozoic–Cambrian Iapetus Ocean rifting and break-up of Rodinia. Specifically, the discoveries include evidence of a failed rifting episode in the supercontinent Rodinia (Chapter 1), geochronological and geochemical data for the igneous activity during the actual rifting (Chapter 2), and the definition of a convergent margin setting for the southwestern Baltica margin during the middle Cambrian (Chapter 3)