Tectonomagmatic Evolution of the Sveconorwegian Orogen Recorded
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Precambrian Research 340 (2020) 105527 Contents lists available at ScienceDirect Precambrian Research journal homepage: www.elsevier.com/locate/precamres Tectonomagmatic evolution of the Sveconorwegian orogen recorded in the T chemical and isotopic compositions of 1070–920 Ma granitoids ⁎ Anette Gransetha, , Trond Slagstadb, Nolwenn Cointb, Nick M.W. Robertsc, Torkil S. Røhrb, Bjørn Eske Sørensena a Department of Geoscience and Petroleum, Norwegian University of Science and Technology, S. P. Andersens Veg 15a, 7031 Trondheim, Norway b Geological Survey of Norway, 7491 Trondheim, Norway c Geochronology and Tracers Facility, British Geological Survey, Nottingham NG12 5GG, UK ARTICLE INFO ABSTRACT Keywords: The Sveconorwegian Province in Southern Norway and Sweden hosts at least four granitoid suites, representing Sveconorwegian orogen apparently continuous magmatism at the SW margin of the Fennoscandian Shield between 1070 and 920 Ma. Mafic underplating This study presents a compilation of published and new zircon LA-ICP-MS U-Pb geochronology, whole-rock and Granitoid magmatism zircon geochemistry and Sm-Nd isotope data for the granitoid suites and demonstrates the granitoids’ ability to Geochemistry record changes in the tectonomagmatic evolution of this orogenic Province. The Sirdal Magmatic Belt (SMB, ca. Sm-Nd isotopes 1070–1010 Ma) represents the earliest magmatism, west in the Province, followed by two hornblende-biotite Trace element modelling granitoid suites (HBG, ca. 1000–920 Ma) and the Flå–Iddefjord–Bohus suite (FIB, ca. 925 Ma), in central and eastern parts of the Province, respectively. The SMB and the HBG bodies located outside of the SMB (referred to as HBGout) are chemically similar, whereas the HBG bodies located in the same region as the SMB (referred to as HBGin) are more ferroan, enriched in incompatible elements and have higher zircon saturation temperatures. Isotopically, the SMB and both HBG suites fall on an evolutionary trend from widespread 1.5 Ga crust in the region, suggesting this was the dominant crustal contribution to magmatism. The FIB suite is more per- aluminous, rich in inherited zircon, and has isotopic compositions suggesting a more evolved source than both the HBG suites and the SMB. Trace element modelling shows that the SMB and HBGout suites could have formed by 50% partial melting of 1.5 Ga crust, whereas 5–10% remelting of the dehydrated and depleted SMB residue accounts for the geochemical composition of the HBGin suite. The available data suggest a scenario where the 1.5 Ga lower crust underwent melting due to long-lived mafic underplating giving rise to the SMB suite. Afterca. 1000 Ma, regional-scale extension may have led to more widespread mafic underplating causing remelting of the residue following SMB melt extraction, forming the HBGin suite, with lower-crustal melting farther east forming the HBGout suite. Changes in melt composition over this 150 Myr time interval may thus be ascribed to an evolving melt source rather than fundamental changes in tectonic regime. Deep continental subduction at ca. 990 Ma, east in the orogen, provided an isotopically evolved crustal source for the FIB suite. The data underline the difference in tectonic processes across the orogen, with long-lived, high temperatures in the westernand central parts and colder, high-pressure events in the eastern parts of the orogen. 1. Introduction source and associated magmatic processes, in turn recording the re- gion’s geodynamic history. Granitoid rocks are the most common magmatic rocks found in the The western and central parts of the late Mesoproterozoic continental crust. They form in various tectonic settings and preserve Sveconorwegian Province in southwestern Fennoscandia was char- evidence of the source and processes that lead to formation of con- acterised by voluminous granitoid and minor mafic magmatism (e.g. tinental crust by growth and reworking (e.g. Goodge and Vervoort, Andersen et al., 2002, 2009; Coint et al., 2015; Eliasson and Schöberg, 2006, Zhao et al., 2008; Zhao et al., 2016). The evidence is stored in the 1991; Slagstad et al., 2018; Vander Auwera et al., 2003). The granitoid geochemical and isotopic composition of the granitoids and tracking magmatism was continuous between 1070 and 920 Ma and has been the variations through time and space gives an indirect view into the subdivided into two periods based on geochronological and ⁎ Corresponding author. E-mail address: [email protected] (A. Granseth). https://doi.org/10.1016/j.precamres.2019.105527 Received 29 August 2019; Received in revised form 25 October 2019; Accepted 1 November 2019 Available online 04 November 2019 0301-9268/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/). A. Granseth, et al. Precambrian Research 340 (2020) 105527 Fig. 1. (A) Main lithotectonic units of the Sveconorwegian Province, separated by shear zones. The location of ca. 990 Ma eclogite in the Eastern Segment is indicated. (B) A more detailed map of the western and central parts of the Sveconorwegian Province highlighting various igneous units discussed in the text. The HBGin, HBGout and FIB suites represent a new tripartite subdivision proposed here for what was originally a single suite of “post-orogenic granitoids”, typically referred to as the hornblende-biotite granitoid (HBG) suite. The colour scheme of the granitoid suites follows the colour scheme used for the plots in this paper. geochemical data. The Sirdal Magmatic Belt (SMB) was emplaced in the rocks was significantly larger, and the Feda augen gneiss is nowcon- west of the orogen between 1070 and 1010 Ma, followed by emplace- sidered part of the much larger SMB suite (Slagstad et al., 2013). The ment of a hornblende-biotite-bearing granitoid (HBG) suite in western presence of older crustal components residing in the Sveconorwegian and central parts of the orogen between 1000 and 920 Ma (Fig. 1). lower crust plays an important role in petrogenetic models proposed for Numerous geochemical studies have been conducted in the Sveco- the HBG suites (e.g. Andersen et al., 2009b; Vander Auwera et al., norwegian Province focussing on a subset of these granitoid suites (e.g. 2011). These crustal components have been invoked to explain the Andersen et al., 2009b, Bingen et al., 1993, Vander Auwera et al., spread in trace element and isotopic composition of HBG magmas. 2003). Falkum (1982), Bingen (1989) and Bingen et al. (1993) identi- Vander Auwera et al., 2003, 2011 interpreted the continuous compo- fied and documented an elongate body of porphyritic granodiorite rich sitional trend of the HBGs to be a result of partial melting and fractional in alkali feldspar phenocrysts in the western parts of the Province, crystallisation of previously underplated basalts formed in a convergent which they referred to as the Feda augen gneiss. This augen gneiss was margin setting and that the source(s) of the HBG suites and Feda (now later dated to ca. 1051 Ma by Bingen and Van Breemen (1998), and SMB) suite were variably contaminated by these components. Alter- interpreted to represent a short-lived magmatic event in a subduction- natively, Andersen et al. (2001, 2009b) argued that the HBG magmas related geodynamic regime. Since the early 2000 s, mapping by the resulted from imperfect mixing between anatectic and mafic, mantle- Geological Survey of Norway (NGU) has shown that the extent of these derived melts. They identified two crustal components residing inthe 2 A. Granseth, et al. Precambrian Research 340 (2020) 105527 Table 1 orthogneisses of plutonic and volcanic origin that formed between ca. Overview of the compiled data and data from this study. Crossed symbols 1650 and 1480 Ma, with associated metasedimentary successions indicate that data exist for the suite, either as whole-rock geochemistry or (Bingen and Viola, 2018, Nijland et al., 2014, Slagstad et al., sub- isotope data or as both. mitted.). The Telemark lithotectonic unit consists of ca. 1585–1480 Ma No. of data Suites volcanic and plutonic suites (Bingen et al., 2005, Roberts et al., 2013, Slagstad et al., submitted.), intruded by a bimodal suite at ca. Refs. Whole-rock Nd SMB HBGin HBGout FIB 1.28–1.20 Ga (Bingen et al., 2002, Brewer et al., 2004, Pedersen et al., Bingen (1989) 27 X 2009, Slagstad et al., submitted.). The 1.5 Ga suite is generally calc- Bingen et al. (1993) 15 10 X alkaline, whereas Nd isotope data indicate relatively juvenile values for Slagstad et al. (2013) 47 X both the 1.5 Ga (between + 1.0 to + 5.3) and the 1.28–1.2 Ga (between Stormoen (2015) 19 X +0.7 to +6.3) suites (Brewer and Menuge, 1998, Brewer et al., 2004). Bogaerts et al. (2003) 43 13 X The Sveconorwegian metamorphic evolution is characterised by geo- Menuge (1988) 6 X Andersen (1997) 13 X graphically and temporally discrete events between 1140 and 920 Ma, Pedersen and Maaløe (1990) 16 X that variably reworked the pre-Sveconorwegian crust (Bingen et al., Welin (1994) 3 X 2008, Slagstad et al., 2017). High-grade metamorphism in the Bamble Pedersen and Konnerup- 12 X X and Kongsberg lithotectonic units at ca. 1140 Ma is typically taken as Madsen (2000) Vander Auwera et al. (2003) 53 17 XX the onset of Sveconorwegian orogenesis (Bingen et al., 2008). Notably, Andersen et al. (2009b) 22 XX sedimentation was active in the Telemark lithotectonic unit until at Andersen et al. (2001) 48 XXX least 1110 Ma (Spencer et al., 2014), with the first high-grade meta- This study 309 30 X X X X morphic events recorded at ca. 1070 Ma (Blereau et al., 2019; Slagstad Total 563 140 et al., 2018), i.e., ca. 70 Myr after the onset in Bamble–Kongsberg. The Bamble–Kongsberg lithotectonic units are separated from the structu- lower crust based on trace elements and Lu-Hf systematics of zircons: a rally lower Telemark lithotectonic unit by a high-strain zone (e.g.