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Chapter 1.1 Tectonic History of Antarctica Over the Past 200 Million Years

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Chapter 1.1 Tectonic History of Antarctica Over the Past 200 Million Years Downloaded from http://mem.lyellcollection.org/ at Dawn Angel on March 2, 2021 Chapter 1.1 Tectonic history of Antarctica over the past 200 million years Bryan C. Storey1* and Roi Granot2 1Gateway Antarctica, University of Canterbury, Christchurch 8041, New Zealand 2Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel RG, 0000-0001-5366-188X *Correspondence: [email protected] Abstract: The tectonic evolution of Antarctica in the Mesozoic and Cenozoic eras was marked by igneous activity that formed as a result of simultaneous continental rifting and subduction processes acting during the final stages of the southward drift of Gondwana towards the South Pole. For the most part, continental rifting resulted in the progressive disintegration of the Gondwana supercontinent from Middle Jurassic times to the final isolation of Antarctica at the South Pole following the Cenozoic opening of the surrounding ocean basins, and the separation of Antarctica from South America and Australia. The initial rifting into East and West Gondwana was proceeded by emplacement of large igneous provinces preserved in present-day South America, Africa and Antarctica. Continued rifting within Antarctica did not lead to conti- nental separation but to the development of the West Antarctic Rift System, dividing the continent into the East and West Antarctic plates, and uplift of the Transantarctic Mountains. Motion between East and West Antarctica has been accommodated by a series of discrete rifting pulses with a westward shift and concentration of the motion throughout the Cenozoic leading to crustal thinning, subsidence, elevated heat flow conditions and rift-related magmatic activity. Contemporaneous with the disintegration of Gondwana and the isolation of Antarctica, subduc- tion processes were active along the palaeo-Pacific margin of Antarctica recorded by magmatic arcs, accretionary complexes, and forearc and back-arc basin sequences. A low in magmatic activity between 156 and 142 Ma suggests that subduction may have ceased during this time. Today, following the gradual cessation of the Antarctic rifting and surrounding subduction, the Antarctic continent is situated close to the centre of a large Antarctic Plate which, with the exception of an active margin on the northern tip of the Antarctic Peninsula, is surrounded by active spreading ridges. At the start of the Mesozoic Era, Antarctica was the centre prior to or during the Gondwana break-up (Randall and Mac piece or keystone to the Gondwana supercontinent which Niocaill 2004). Haag Nunataks is a small fragment of had remained stable for almost 350 myr. During that time, Gondwana drifted southwards from a more equatorial position (Torsvik et al. 2012). The slow southward drift was temporally disrupted at c. 250 Ma as Gondwana voyaged north but headed south again at c. 200 Ma (Torsvik and Cox 2013). In middle Jurassic times, the progressive disintegration of the supercontinent changed the global continental configuration, leading to the opening of major ocean gateways and the isola- tion of Antarctica at the South Pole. Today, the tectonic Ant- arctic Plate is bordered by six different tectonic plates and is almost entirely surrounded by spreading ridges with Cenozoic isolation upon the South Pole. The Antarctic continent can be divided into two physio- graphical provinces, East and West Antarctica, separated by a spectacular mountain range, the Transantarctic Mountains (TAM), that stretch from north Victoria Land bordering the western Ross Sea to the Weddell Sea (Fig. 1). Cratonic East Antarctica comprises Archean and Proterozoic–Cambrian ter- ranes amalgamated during Precambrian and Cambrian times (Fitzsimons 2000). In contrast, West Antarctica comprises a collage of five tectonic blocks separated by rifts and topo- graphical depressions (Fig. 1): the Antarctic Peninsula, Thur- ston Island, the Ellsworth Whitmore Mountains (EWM), Haag Nunataks and Marie Byrd Land (Dalziel and Elliot 1982). The Antarctic Peninsula has generally been considered as a near- complete Mesozoic–Cenozoic continental arc system formed above an eastward-dipping palaeo-Pacific subduction zone (Suarez 1976; Burton-Johnson and Riley 2015). However, Vaughan and Storey (2000) suggested that the Antarctic Pen- Fig. 1. Tectonic map of Antarctica superimposed on a satellite-derived insula may have consisted of three fault-bounded terranes that free-air gravity field (offshore: Sandwell et al. 2014) and sub-ice amalgamated in Late Cretaceous time (Albian). The Ellsworth topography (Fretwell et al. 2013) showing the Transantarctic Mountains Whitmore Mountains block is a displaced fragment of the (TAMts), the crustal blocks of West Antarctica and the West Antarctic Rift Permo-Triassic Gondwanide Fold Belt that was originally System (WARS). AP, Antarctic Peninsula; EWM, Ellsworth Whitmore located in the Natal Embayment off South Africa in Gond- Mountains; HN, Haag Nunataks; MBL, Marie Byrd Land; TI, Thurston wana before undergoing 90° counter-clockwise rotation Island. From: Smellie, J. L., Panter, K. S. and Geyer, A. (eds) Volcanism in Antarctica: 200 Million Years of Subduction, Rifting and Continental Break-up. Geological Society, London, Memoirs, 55, https://doi.org/10.1144/M55-2018-38 © 2021 The Author(s). Published by The Geological Society of London. All rights reserved. For permissions: http://www.geolsoc.org.uk/permissions. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://mem.lyellcollection.org/ at Dawn Angel on March 2, 2021 B. C. Storey and R. Granot Neoproterozoic craton similar to parts of East Antarctica provided little support for major motion and rotation of crustal (Millar and Pankhurst 1987). In contrast, the Thurston Island blocks during Jurassic extension in the Weddell Sea region (Pankhurst et al. 1993; Riley et al. 2016) and Marie Byrd Land (Jordan et al. 2017). Jordan et al. (2017) proposed an alterna- blocks (Mukasa and Dalziel 2000) contain Mesozoic tive model that predicts c. 500 km of movement of the Haag subduction-related magmatic rocks. In parallel to these pro- and the Ellsworth microplates with 30° of block rotation dur- cesses, a long rift, the West Antarctic Rift System, has ing crustal extension in a Weddell Sea rift zone. In this model, evolved, leading to the dismembering of the plate into the the Weddell Sea rift zone would have formed in response to East and West Antarctic plates. distributed crustal extension within a broad plate boundary This paper reviews the tectonic history of Antarctica during region between East and West Antarctica. To reconcile the the Mesozoic and Cenozoic eras which provides the backdrop geological and palaeomagnetic data from the crustal blocks, for the volcanic and magmatic evolution of the continent. The they suggest that 60° of rotation that is unaccounted for by magmatic evolution in itself provides valuable insights into the geophysically imaged Jurassic extension may have the lithospheric and tectonic processes that shaped the Antarc- occurred earlier during the Gondwanian orogenesis. This is tic continent. Three interacting tectonic processes affected possible within the transpressional tectonic regime suggested Antarctica during the last 200 myr: continental break-up, rift- by Curtis (1997) for Gondwanian events. ing and subduction. The final break-up and separation of East and West of Gond- wana was initiated (at c. 167 Ma) along a rift zone which com- prised the Somali and Mozambique basins, the southern Africa–East Antarctica (Dronning Maud Land) conjugate mar- Continental break-up gins, and the Weddell Sea embayment, with seafloor spreading commencing about 160–165 myr before propagating clock- The initial fragmentation of the Gondwana supercontinent was wise around Antarctica (Ghidella et al. 2002; Konig and preceded by several major tectonic and igneous events prior to Jokat 2006; see the review by Torsvik et al. 2008). Early earliest seafloor spreading in the Jurassic (Dalziel et al. 2013): Africa–Antarctic spreading offshore Dronning Maud Land (1) Latest Paleozoic–early Mesozoic Gondwanide orogene- has been dated as magnetic anomaly M24 (c. 150 Ma: Roeser et al. 1996; Jokat et al. 2003; Malinverno et al. 2012), with the sis and formation of the Gondwanian Fold Belt that fl extended from the Sierra de la Ventana of Argentina, earliest sea oor in the Weddell Sea dated at 147 Ma (Konig and Jokat 2006). A model for the early Indian–Antarctic through the Cape Fold Belt in southern Africa to the Pen- fl sacola Mountains along the Transantarctic margin of spreading system places the onset of sea oor spreading in East Antarctica (Du Toit 1937). The enigmatic Gondwa- the Enderby Basin at anomaly M9 (130 Ma: Gaina et al. nide folding may have developed in response to either 2007), consistent with the opening history between India and flat-slab subduction (Lock 1980), perhaps due to the Australia (Williams et al. 2013). Although volcanism preceded impingement of a buoyant mantle plume beneath the the initial break-up of Gondwana in Middle Jurassic times, the subducting slab (Dalziel et al. 2000), or in response to separation of India from Antarctica c. 130 Ma was followed by subduction-related dextral compression along the con- volcanic activity, with the earliest magmatic activity in the Ker- vergent SW margin of Gondwana (Curtis 1997). guelen area dated to c. 118 Ma (Frey et al. 2000; Nicolaysen – et al. 2001). Early Australia–Antarctic spreading has been (2) Early Jurassic
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