Mode and timing of granitoid magmatism in the Västervik area (SE Sweden, Baltic Shield): Sr–Nd isotope and SIMS U–Pb age constraints

Autor: W. Baero, F. Wilsky, Ilka C. Kleinhanns, Bent T. Hansen, Martin J. Whitehouse, Ronny Schoenberg, Nicole Nolte
Rok vydání: 2015
Předmět:
Zdroj: Lithos. :321-337
ISSN: 0024-4937
Popis: Observed geochemical and geophysical signatures in the southern Svecofennian domain (SD) and the Transscandinavian Igneous Belt (TIB) are explained through a model of tectonic cycling and episodic south-westward migration of a subduction zone system. The Vastervik area is located between these two major tectonic domains and as such has received much attention. Granitoids of the Vastervik area were recently re-grouped and classified within the context of this larger regional tectonic model, but a discrepancy between previous relative age estimations and the few available granitoid age determinations was noted. To address this issue, we have dated 13 granitoid samples using a high spatial resolution secondary ion mass spectrometry (SIMS) U–Pb technique. Our new results constrain the intrusion of the majority of granitoids to 1819–1795 Ma, thus placing them into the TIB-1 period. This age range also encompasses our new ages from the central granodiorite belt and the Oro-Hamno pluton, demonstrating a previous overestimation of older granitoid generations in the Vastervik area. Nonetheless, it is shown that Askersund/TIB-0 magmatism, represented by an augen gneiss sample dated to 1846 Ma, is unambiguously present as far south as the Vastervik region. The anatectically generated leucogranites reveal TIB-1 ages and, as expected, older inherited zircon derived from the parental metasedimentary Vastervik formation. By simple Sr–Nd isotope modeling it is further possible to deduce that most TIB-1 granitoids follow a simple (assimilation-) fractional crystallization petrogenetic trend. The youngest granitoid generation was produced through low-pressure fluid-absent crustal melting. In conclusion, granitoids of the Vastervik area fit well into the proposed model for south-westward migration of a subduction zone system active in the Svecofennian domain and represent a new tectonic cycle. It is therefore possible to link the Svecofennian domain and the Transscandinavian Igneous Belt within a single evolutionary scenario explaining the observed granitoid petrology, geochemistry and geochronology. The study area is located at the edge of a particularly long-lived active continental margin that started to operate during the supercontinent Columbia at ca. 1.8 Ga and the presented model explains how this margin initiated at its eastern end.
Databáze: OpenAIRE