Struktura prekambryjskiego podłoża wschodniej części bloku górnośląskiego (Brunovistulicum)

Abstract

Structure of the Precambrian basement of the eastern part of the Upper Silesian block (Brunovistulicum).A b s t r a c t. Two large, regional tectonic units, represented by Małopolska and Brunovistulicum blocks (terrains) can be distinguished in the southern Poland. The Cracow–Lubliniec fault zone forms their border. They vary both in the structures of the Precambrian basement and the Paleozoic rock cover, which shows different paleogeographic-facies and paleotectonic development. They are separated from the neighboring tectonic units by immense deep fault zones. Archean and Early Proterozoic metamorphic rocks within the Rzeszotary horst (2.6–2.8 and 2.0 Ga) are the oldest formations building the Brunovistulicum basement. Farther to the west, Precambrian and Ediacaran anchimetamorphic siliclastics can be observed. Cadomian Precambrian rocks (640–545 Ma), which outcrop only near Brno, occur south and west of them. In the western part of the Brunovisitulicum (theWestern Sudetes) Variscan orthogneiss occurs. The age of its protholite varies vastly; from approximately 1020 Ma through 680–570 Ma to approximately 520–500 Ma. Precambrian basement of the Brunovistulicum is heterogenic. Within the area of Poland, it is formed by two fragments of the crust, represented by Karelian and Early Karelian rocks of the Rzeszotary horst and Cadomian crystalline and anchimetamorphic rocks occurring west of Rzeszotary. Between them, two vast, connected together, magnetic maxima in the vicinity of Tychy and Jordanów can be observed in a magnetic field image Z. The origin of those anomalies is related to the occurrence of gabbro, diabase and/or ultrabasite (ophiolite) rocks. Referring to the earlier concepts, it may be currently assumed that the anomaly axis Tychy–Jordanów determines the course of the contact zone (ophiolite suture zone) between the two fragments of the crust of different ages, building the basement of Brunovistulicum: the Archean — Lower Proterozoic (Karelian) and the Upper Proterozoic (Cadomian) formations.