Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 Pannotia to Pangaea: Neoproterozoic and Paleozoic Orogenic Cycles in the Circum-Atlantic Region: A celebration of the career of Damian Nance J. Brendan Murphy1,2*, Robin A. Strachan3 and Cecilio Quesada4 1Department of Earth Sciences, St Francis Xavier University, Antigonish, Nova Scotia, B2G 2W5, Canada 2Earth Dynamics Research Group, the Institute for Geoscience Research (TIGeR), School of Earth and Planetary Sciences, Curtin University, WA 6845, Australia 3School of the Environment, Geography and Geosciences, University of Portsmouth, Portsmouth PO1 3QL, UK 4Instituto Geológico y Minero de España (IGME), C/Ríos Rosas, 23, 28003 Madrid, Spain JBM, 0000-0003-2269-1976 *Correspondence: [email protected] Special Publication 503 celebrates the career of between tectonic events and biogeochemical cycles, R. Damian Nance. It features 27 articles, with more as exemplified in the late Neoproterozoic–Early than 110 authors based in 18 different countries. Cambrian by the amalgamation of Gondwana span- The wide range of topics presented in this volume ning a time interval characterized by dramatic climate mirrors the breadth and depth of Damian’s contribu- swings, profound changes in the chemistry of the tions, interests and expertise. Like Damian’s papers, oceans and atmosphere, and the evolution of multi- the contributions range from the predominantly con- cellular animals (see Hoffman 1991; Hoffman et al. ceptual to detailed field work, but all are targeted at 1998; Narbonne 2010; Knoll 2013). understanding important tectonic processes. Their As reconstructions became more refined, scope not only varies in scale from global to regional several authors proposed that Gondwana was part to local, but also in the range of approaches required of a larger entity called Pannotia that included Lau- to gain that understanding. Thus, there are contribu- rentia, Baltica and possibly Siberia (e.g. Stump tions on the processes responsible for the formation 1987; Dalziel 1997). Recent syntheses have con- and breakup of supercontinents, the controversial tested the status of Pannotia as an Ediacaran super- amalgamation of Pannotia, the generation and continent because of its small size relative to destruction of Paleozoic oceans, and the development Pangaea (about half) and limited duration (it was of the Appalachian–Ouachitan–Caledonide–Varis- probably breaking up in its centre as continents can orogens (Fig. 1). In addition to field work, the were colliding with its margins). Rodinia, which approaches to gain that understanding include exam- amalgamated during global-scale c. 1.1–0.9 Ga oro- ining the relationships between stratigraphy and genesis, is arguably the most widely accepted of the structural geology, precise geochronology, geo- pre-Pangaean supercontinents (McMenamin and chemical and isotopic fingerprinting, geodynamic McMenamin 1990; Li et al. 2008). Many syntheses modelling, regional syntheses, palaeogeographic claim that the transition from Rodinia to Pangaea modelling, and plain, old-fashioned arm-waving! represents a single supercontinent cycle (e.g. Li et al. 2019). Resolution of the ‘Pannotia contro- versy’ is fundamental to understanding the supercon- The Pannotia controversy tinent cycle. If the transition from Rodinia to Pangaea represents a single supercontinent cycle, When Damian with Tom Worsley and Judith Moody then Pangaea probably formed by extroversion, i.e. proposed the existence of a supercontinent cycle with predominantlysubductionof the exterior oceansystem a series of papers in the 1980s (Nance et al. 1986; that surrounded Rodinia (Li et al. 2019). In contrast, Moody et al. 1988), the amalgamation of Gondwana Murphy and Nance (2008) maintain that Pannotia in the Neoproterozoic, as evidenced by the collisional formed by the amalgamation of the ocean exterior to Pan-African orogenic events, was arguably their best Rodinia (extroversion), but that Pangaea was formed defined pre-Pangaean supercontinent. These early from Pannotia by closure of the interior Iapetus and publications examined the potential relationship Rheic oceans (introversion). From: Murphy, J. B., Strachan, R. A. and Quesada, C. (eds) 2020. Pannotia to Pangaea: Neoproterozoic and Paleozoic Orogenic Cycles in the Circum-Atlantic Region. Geological Society, London, Special Publications, 503, https://doi.org/10.1144/SP503-2020-213 © 2020 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/). Published by The Geological Society of London. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics Downloaded from http://sp.lyellcollection.org/ by guest on September 27, 2021 J. B. Murphy et al. Gondwanan margin beginning at c. 0.6 Ga. Candi- dates for plume magmatism are identified that require testing by detailed field, geochemical and isotopic studies. Heron et al. (2020) present 3-D global convec- tion models showing increased core–mantle heat flux during the convergence that led to Pan-African collisions and amalgamation of Pannotia. This heat flux is similar in magnitude to that associated with convergence and assembly of Rodinia and Pangaea, implying that Pannotia assembly may have impacted mantle circulation patterns in a similar manner. Evans (2020) argues against the existence of Pannotia as a landmass, claiming that its existence is not supported by either the geological record or indirect proxies (e.g. biological diversity, palaeo- climate, sea-level, magmatism and palaeoenviron- mental indicators). Evans does agree with Murphy Fig. 1. Palaeocontinental reconstruction (c. 500 Ma; at al. and Heron et al. that the assembly of Gondwana after Domeier 2016) showing the relative locations of was probably a geodynamically significant event on the contributions to this volume. Events in many of the a global scale and merits the status of ‘semi- papers span a considerable duration of time, or may supercontinent’ (see Evans et al. 2016). deviate in time from c. 500 Ma so that the location et al. shown on this map is not necessarily intended to Kroner (2020) test the hypothesis of a provide a geological context for tectonic events Pannotian supercontinent by combining geological documented in the papers. Papers 1–4 (Murphy et al., and palaeogeographical constraints from different Heron et al., Evans and Kroner et al.) are global studies regions. They reconstruct the Paleozoic kinematics and their locations are not shown. 5, Hoffman; 6, van of Laurentia, Gondwana, Siberia and the peri- Staal et al.; 7, Arenas et al.; 8, Lindner et al.; 9, Errami Gondwanan terranes relative to the East European et al.; 10, Andresen; 11, Dalslåen et al.; 12, Slagstad Craton (including Baltica). Their approach is to et al.; 13, Walker et al.; 14, McConnell et al.; 15, ‘back-rotate’ from a Pangaea-A configuration to Archibald and Murphy; 16, Schofield et al.; 17, Dostal et al.; 18, Hildebrand and Whalen; 19, Piper and accommodate the Paleozoic opening of the Iapetus, Pe-Piper; 20, Park and Hinds; 21, Dennis, 22., Rheic and Paleo-Arctic oceans. These back rotations Juárez-Zúñiga et al.; 23, Álvaro et al.; 24, Sánchez achieve a Pannotia configuration, thus supporting Martinez et al.; 25, Gutiérrez-Alonso et al.; 26, their interpretation of its status as a supercontinent Paslawski et al.; 27, Pereira et al. Abbreviations: FA, and indicating that the transition from Rodinia to Pan- Famatina; MX, Mexico; CA, Carolinia; WA, West gaea represents two complete supercontinent cycles. Avalonia; EA, East Avalonia; IB, Iberia; AM, They also identify two fundamental phases of Iapetus Armorica; CH, Clew Bay-Highland Border; MV, Ocean opening and closure. Midland Valley–South Mayo; DW, Dashwoods; LB, Lushes Bight; PI, Eastern Piedmont; CU, Cuyania. Regional Neoproterozoic tectonics In this volume, four papers (Murphy et al., Heron et al., Evans and Kroner et al.) tackle the con- The Neoproterozoic Era was characterized by colli- troversial status of Pannotia as an Ediacaran super- sional (Pan-African) orogenic belts as Gondwana continent. Murphy et al. (2020) point out that an amalgamated, and by subduction-related orogenesis over-arching question is whether the assembly of along its periphery. In the Pan-African collisional the Gondwanan portion of Pannotia influenced belt of Namibia, Hoffman (2020) describes the global-scale mantle convection patterns (Nance and stratigraphic and structural record of a lithospheric Murphy 2019; Pastor-Galán et al. 2019). Such pat- cusp (or syntaxis). Such cusps (where arcs are terns, if they existed, must be factored into models joined end-to-end) are features of modern arc sys- for the amalgamation of Pangaea. Deducing the tems, associated with the buckling of subducted mantle legacy (mantle convection patterns) of Pan- slabs, but are rarely identified in the geological notia’s amalgamation is fundamental to resolving record. Hoffman describes a potential cusp where this controversy. Murphy et al. propose a testable sce- the Kaoko belt and the Damara orogen meet at nario involving feedback between the supercontinent right angles. In the vicinity of the hypothesized cycle and global mantle convection patterns. This cusp, the regional stratigraphy dominated by marine predicts upwellings beneath the Gondwanan portion carbonates was uplifted to form a megakarst land- of Pannotia and the arrival of plumes along the entire scape with associated mass slides and was then Downloaded from http://sp.lyellcollection.org/