Sveconorwegian orogeny

Sveconorwegian orogeny
Name	Sveconorwegian orogeny
Date	~1140 to 900 million years ago
Orogeny type	Continental collision
Affected area	Southwest Scandinavia, Baltic Shield
Geology	Gneiss, Granulite, Anorthosite

Sveconorwegian orogeny. The Sveconorwegian orogeny was a major Proterozoic mountain-building event that profoundly shaped the crust of southern Scandinavia and adjacent regions. Occurring during the Mesoproterozoic to early Neoproterozoic, it involved the collision of several continental blocks against the growing edge of the ancient Baltica continent. This prolonged tectonic episode resulted in extensive metamorphism, magmatism, and the assembly of crustal segments that form the bedrock of modern Norway and Sweden.

Overview

The Sveconorwegian orogeny represents the final major Precambrian assembly of the Baltic Shield, forming a continuous Grenvillian-age belt with orogenies in Laurentia. It is named for its prominent exposures in southwestern Norway and Sweden, with key geological studies conducted by institutions like the Geological Survey of Sweden and the Norwegian Geological Survey. The event created a vast, deeply eroded mountain chain, the roots of which are now exposed as high-grade metamorphic rocks and large igneous intrusions. Its timing and nature are crucial for reconstructing the supercontinent Rodinia.

Tectonic setting and causes

The orogeny occurred in a complex tectonic setting involving the convergence of the Baltica continent with other continental fragments, potentially including Amazonia. This convergence was part of the global amalgamation of the Rodinia supercontinent. The primary driving mechanism was the closure of an ancient ocean basin, leading to continental collision and subduction. Key evidence for this setting comes from studies of ophiolite remnants and island arc sequences within the Sveconorwegian Province.

Geochronology and phases

Geochronological data, primarily from U-Pb dating of zircon and titanite, define the orogeny as occurring between approximately 1140 and 900 million years ago. It is subdivided into several tectonic phases. An early phase (~1140–1080 Ma) involved accretion and arc magmatism, recorded in the Bamble Terrane and Kongsberg Terrane. The main collisional phase (~1050–980 Ma) saw peak metamorphism and crustal thickening. A later phase (~980–900 Ma) involved post-collisional extension and the emplacement of large pegmatite suites.

Regional geology and terranes

The Sveconorwegian orogen comprises several distinct crustal blocks or terranes sutured together. From east to west, major units include the Eastern Segment, the Idefjorden Terrane, the Kongsberg Terrane, the Bamble Terrane, and the Telemarkia Terrane. The boundary between the Eastern Segment and the western terranes is marked by the major Mylonite Zone shear zone. The Rogaland Anorthosite Province, with its massive anorthosite and norite intrusions, is a hallmark of the orogen's westernmost region.

Metamorphic and magmatic features

The orogen is characterized by widespread high-grade metamorphism, reaching granulite facies conditions in areas like the Bamble Terrane and parts of the Kongsberg Terrane. This produced mineral assemblages with garnet, orthopyroxene, and sillimanite. Major magmatic events include the emplacement of the ~930 Ma Rogaland Anorthosite Province and voluminous ~920 Ma granite suites, such as the Hornblende granites. Extensive systems of pegmatite dikes, some bearing rare minerals, were formed during the late-stage collapse of the orogen.

Correlation with other orogenies

The Sveconorwegian orogeny is widely correlated with the Grenville orogeny in Laurentia, forming part of a global network of orogenic belts that stitched together the supercontinent Rodinia. It also shows temporal links with the Sun Sveconorwegian event in Svalbard and the Avalonian orogenic cycle. These correlations are supported by similar age patterns, paleomagnetic data, and comparisons of detrital zircon signatures from sedimentary basins across former continental margins.

Category:Geology of Norway Category:Geology of Sweden Category:Orogenies Category:Proterozoic