How the closure of paleo-Tethys and Tethys oceans controlled the early breakup of Pangaea D. Fraser Keppie Department of Energy, Government of Nova Scotia, Joseph Howe Building, 12th Floor, 1690 Hollis Street, Halifax, Nova Scotia B3J 3J9, Canada ABSTRACT fined to segments south of Newfoundland dur- Two end-member models have been invoked to accommodate the Mesozoic dispersal ing the Jurassic and early Cretaceous and did of the supercontinent Pangaea. In one end-member, the opening of the Atlantic Ocean is not extend further to the north until the late Cre- inferred to have been balanced by the closure of the Panthalassan Ocean related to subduc- taceous (Buiter and Torsvik, 2014). tion off the western margins of the Americas. In the other end-member model, the opening In this study, I investigate the processes of the Atlantic Ocean is accommodated by the closure of the paleo-Tethys and Tethys oceans responsible for the failure and dispersal of Pan- linked to subduction off the southern margins of Eurasia. Here, I re-evaluate global plate gaea by re-evaluating the global plate circuit circulation data compiled for the middle Mesozoic Era. The present evaluation confirms data compiled for the Mesozoic era (Seton et that closure of the paleo-Tethys and Tethys oceans compensated for the early opening of the al., 2012) and identifying the compensation central Atlantic and proto-Caribbean oceans. This result implies that the tectonic evolution system(s) that accommodated the early stages of the North American Cordillera was independent from the processes governing Pangaea of central Atlantic and proto-Caribbean rifting breakup in the Jurassic and Early Cretaceous Periods. As well, the opening Atlantic and (Fig. 1). By identifying explicitly the oceanic closing Tethys realm must have been tectonically connected through the Mediterranean domains that closed to accommodate the open- region in terms of a transform fault or point yet to be factored into geological interpre- ing of the Atlantic domain, it is possible to con- tations. Tight geometric and kinematic correlations evident between the opening Atlantic sider the fundamental links that existed between and closing Tethyan domains can be demonstrated, which are most readily explained if rifting and sea-floor spreading within the Pan- the forces causing Pangaea breakup were transmitted from the Tethyan domain into the gaean interior and the subduction and seafloor Atlantic domain, and not vice versa. Thus, slab sinking–based forces produced during the consumption at its peripheral margins. evolution of the Tethyan subduction zones are hypothesized to have controlled the early Two competing models of compensation Atlantic breakup of Pangaea. for the Mesozoic opening of the central Atlan- tic exist. In the Atlantic-Panthalassan model, INTRODUCTION forces imparted at subduction zones peripheral the opening of the central Atlantic and proto- Why Pangaea broke up where and when it to Pangaea provided the motivation for super- Caribbean oceans is inferred to have been bal- did remains an open question in modern tec- continent failure (Hamilton, 2007). A number of anced by subduction under the Cordilleran tonics (Nance et al., 2014). Yet, resolution of geometric and kinematic properties of Pangaea margin of North America and partial closure of these questions are central to understanding the breakup continue to be enigmatic. It is unclear the Panthalassan oceanic domain (e.g., Pindell driving mechanisms of supercontinent breakup why re-activation of the late Paleozoic sutures and Dewey, 1982; Johnston and Borel, 2007; and plate tectonic processes (Morra et al., preserved in Pangaea following the collision of Miall and Blakey, 2008; Sigloch and Mihaly- 2013; Buiter and Torsvik, 2014). Recent studies Laurentia and Gondwana were preferred over nuk, 2013). In the alternative Atlantic-Tethyan appear to favor models in which a superplume the re-activation of other structural lineaments model, the opening of the central Atlantic and in the sublithospheric mantle beneath the cen- preserved within Pangaea (Buiter and Torsvik, proto-Caribbean oceans is inferred to have been tral Atlantic provides the key drive (Nance et al., 2014). And, it is also unclear why reactivations balanced by the closure of the paleo-Tethys and 2014). An alternative possibility is that tectonic of the late Paleozoic sutures were mostly con- Tethys oceans located south of Eurasia (e.g., Figure 1. Reconstructed 125 Ma Rift Margins (MR = Mid−Ocean Ridge) paleo geography of Earth I F PTC (AMR) Atlantic (TMR) Tethys at 125 Ma (after Seton et TC (CMR) Caribbean (SMR) Somali al., 2012) with South Af- N TMR Trench Margins (C = Cordillera) rica held fixed. The com- AMR NAC (NAC) North American (PTC) Palaeo−Tethys pensation between ocean SMR (MAC) Middle American (TC) Tethys opening and closing prior CMR (SAC) South American to ca. 125 Ma is indicated Stage Poles with light and dark shaded MAC 185 175 165 155 145 135 125 End Age (Ma) polygons, respectively, in SAC Eurasia Figures 2–4. Ocean com- Neolaurentia pensation must be con- (period = 20 Ma; fixed = Neogondwana) nected via one of three Ocean Breakup Tree Time (Ma) end-member transform Compensation systems involving sinistral g Continents −225 −200 −175 −150 −125 −100 −75 −50 −25 0 Neolaurentia Eurasia transform (TS), polar trans- Closin form (T ), or dextral trans- Eurasia Paper Scope P TD form (TD) deformation. La- TP Neolaurasia Neolaurentia T Sinoria beled continental polygons S discussed in text include g Cimmeria Pangaea Neogondwana Africa Newfoundland (N), Iran (I), Openin Neogondwana and Farah (F). Simplified India+ South America Pangea breakup tree indi- cates scope of paper. GEOLOGY, April 2015; v. 43; no. 4; p. 335–338 | doi:10.1130/G36268.1 | Published online 27 February 2015 GEOLOGY© 2015 Geological | Volume Society 43 | ofNumber America. 4 Gold| www.gsapubs.org Open Access: This paper is published under the terms of the CC-BY license. 335 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/43/4/335/3548497/335.pdf by guest on 27 September 2021 Collins, 2003; Kovalenko et al., 2010). The bility of west-dipping subduction off the west METHODOLOGY goal of the present study is to evaluate which of coast of North America—under Cordilleran Stage poles for the net motion of North these compensation systems governed the early terranes with a hypothetically allochthonous America (Neolaurentia) away from South Africa breakup of Pangaea. origin—has also been proposed (Moores, 1970; (Neogondwana) were calculated using 20 m.y. Complexities in the Atlantic breakup of Pan- Johnston and Borel, 2007; Sigloch and Mih- stage intervals for 10 m.y. time steps between gaea include the opening of the South Atlantic alynuk, 2013). Detrital zircon data indicate that 185 Ma and 125 Ma (squares in Fig. 1). Simi- rift at ca. 125 Ma (Seton et al., 2012), a major many of the outboard Cordilleran terranes have larly, stage poles for the net motion of Eurasia change in global tectonics at ca. 105–100 Ma a peri-Laurentian provenance by Triassic time toward South Africa were calculated (triangles (Matthews et al., 2012), and the opening of the (Colpron and Nelson, 2009), but debate persists in Fig. 1). These poles constrain how north- North Atlantic rift at ca. 90 Ma (Seton et al., on the timing, orientation, and polarity of Cor- ern Pangaea (Neolaurentia + Eurasia) moved 2012). For reasons of simplicity and space, I con- dilleran subduction zones throughout the Juras- with respect to southern Pangaea (Neogond- fine the present evaluation of the early breakup of sic and Cretaceous (Johnston and Borel, 2007; wana) before 125 Ma. The implications of Pangaea to the period of time prior to ca. 125 Ma. Miall and Blakey, 2008; Sigloch and Mihal- these motions for opening and closing oceanic However, I also do not consider the late Jurassic ynu, 2013). A few studies have suggested that domains are then illustrated by constructing breakup of southern Pangaea (or Neogondwana) Tethyan—not Panthalassan—closure compen- unshaded (ocean opening) and shaded (ocean because it can be shown that the opening of the sated for early Atlantic opening instead (e.g., closing) parallelograms for the net relative Somali rift (between Africa–South America and Collins, 2003; Kovalenko et al., 2010). motion of the major plates away from or toward Madagascar-India-Australia-etc.) took place with North-dipping subduction is conventionally one another, respectively, for given stage inter- kinematics broadly perpendicular to the Atlantic inferred along or adjacent to the southern mar- vals (Figs. 1–4). Kinematic consistency between breakup investigated here (e.g., Reeves et al., gins of Eurasia and, subsequently, Cimmeria an opening ocean domain and a closing ocean 2004; Seton et al., 2012). The scope of the pres- to accommodate the respective closures of the domain requires one of three possible transform ent paper in space and time is given in Figure 1 paleo-Tethys and then Tethys Oceans (Moores, connections: (1) a dextral-transform connection relative to a simplified Pangaea breakup tree. 1970; Collins, 2003; Gaina et al., 2013). Sea- (TD, Fig. 1), (2) a polar transform connection (TP, floor spreading in the Tethys Ocean would have Fig. 1), or (3) a sinistral-transform connection PREVIOUS WORK accommodated the transfer of Cimmeria from (TS, Fig. 1). Reconstructions of Pangaea and its Meso- East Africa to southern Europe (Golonka, 2007). In Figures 2–4, the net opening of the Atlan- zoic-to-present dispersal have been iteratively For convenience, the term Greater Tethyan tic domain and corresponding closure of Greater refined for the past 50 yr with the compilation of domain is used here to name the total oceanic Tethys was calculated for early Jurassic (203– Seton et al. (2012) used herein. Plate boundar- domain that encompassed both the paleo-Tethys 170 Ma), late Jurassic (170–145 Ma), and early ies interpreted to have accommodated Pangaea and Tethys Oceans in the Mesozoic.