Permian-Triassic Tethyan realm reorganization: Implications for the outward Pangea margin

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Highlights

  • We studied a Permian-Triassic thermal anomaly along the Gondwana margin.

  • We show that this thermal anomaly is linked to Tethyan realm reorganization.

  • Slab verticalization triggered asthenospheric upwelling in the South America margin.

Abstract

We present a new conceptual model to explain the first order Permian-Triassic evolution of the whole > 30 000 km long Pangea margin facing the Panthalassa ocean. Compilation of available geological, geochemical, geochronogical and paleomagnetic data all along this system allowed us to distinguish three part of the margin: western Laurentia, western Gondwana and eastern Gondwana. These segments record distinct tectonic and magmatic events, which all occur synchronously along the whole margin and correlate well with the main geodynamic events of this period, i.e. subduction of the Paleotethys mid-ocean ridge at 310-280 Ma, opening of the Neotethys at 280-260 Ma, counterclockwise rotation of Pangea at 260-230 Ma and closure of the Paleotethys at 230-220 Ma. Between 260 and 230 Ma, the reorganization of the Tethyan realm triggered the up to 35° rotation of Pangea around an Euler pole located in northernmost South America. This implied both an increase and a decrease of the convergence rate between the margin and the Panthalassa ocean, north and south of the Euler pole, respectively. Thus, the Permian-Triassic Pangean margin was marked: in western Laurentia by marginal sea closure, in western Gondwana by widespread bimodal magmatic and volcanic activity, in eastern Gondwana by transpressive orogenic phase. Therefore, we propose that the Permian-Triassic evolution of the outward margin of Pangea was controlled by the Tethyan realm reorganization.

Introduction

From Early Permian to Late Triassic, the Earth surface recorded drastic modifications including: (1) final amalgamation of the Pangean supercontinent, (2) Tethyan realm reorganization marked by the subduction of the Paleotethys ridge under the Laurussia and Asian margins (310-280 Ma), the onset of the Neotethys opening at 280-260 Ma (Stampfli and Borel, 2002), and the northward drifting of Cimmerian blocks synchronous with the subduction of the Paleotethys until ∼225 Ma (Pullen et al., 2008), (3) mantle activity expressed by the outpouring of Large Igneous Provinces (LPs) (Golonka and Bocharova, 2000), and (4) early rifting of Pangea coeval with the Cantabrian orogen in western Europe (Gutiérrez-Alonso et al., 2008) (Fig. 1).

Based on compilation of worldwide geological data, Gutiérrez-Alonso et al. (2008) proposed that between 310 and 280 Ma, the subduction of the Paleotethys mid-ocean ridge under Laurussia triggered a redistribution of the stress-strain regime throughout the Pangea supercontinent during rigid-body rotation. This plate-scale model, based on the Paleotethys slab pull, accounts for the widespread radial rifting systems recorded all around the core of the Cantabrian orogen in Early Permian times (including the Neothethys, Madagascar, Oslo, North Sea and Siberian rifts). Following this event, the Neotethys opened at ca. 280-260 Ma and inner Pangean deformation and magmatism abruptly ended.

Here, we explore the evolution of the outward Pangea margin facing the Panthalassa subduction. For this, we use a compilation of available geochronological, geochemical, geological and paleogeographic data along the outward Pangean margin, from Laurussia to eastern Gondwana. Along this outward Pangean margin. We distinguish three main segments on the basis of their self-consistent evolution: western Laurentia, western Gondwana and eastern Gondwana (Fig. 1). These segments show synchronous but distinct changes in their magmatic and tectonic setting at 280–265, 265–230 and 230-220 Ma. These changes coincide with subduction of the Paleotethys ridge, opening of the Neotethys ocean and closure of the Paleotethys ocean, respectively, and with overall changes in apparent pole wandering path of Pangea. As no other investigated model can explain such plate-scale and synchronous events, we hypothesize that the Permian-Triassic counterclockwise rotation of Pangea shown by paleomagnetic and paleoenvironment studies (Marcano et al., 1999, Golonka, 2007, Torsvik et al., 2012), likely caused by opening of the Neotethys, triggered the major changes in tectonic and magmatic setting recorded all along the margin. Considering the position of the studied segments with respect to the position of the Permian-Triassic Euler pole of rotation of Pangea, the conceptual model presented here fairly explains the observed tectono-magmatic changes along the whole outward Pangea margin, i.e. on more than 30 000 km long.

Section snippets

Permian Triassic evolution of the outward Pangea margin

We compiled the salient available data of the Late Paleozoic to early Mesozoic evolution of the Panthalassa margin from northwestern Canada to east Australia (Fig. 2 and supplementary data). We describe this large-scale geodynamic system by studying the main three representative segments of the margin: western Laurentia, western Gondwana and eastern Gondwana. We do not integrate the evolution of north Laurussia as very few data are available. The Permian-Triassic evolution of the Asian

Main Permian-Triassic geodynamic events along the outward Pangea margin

From Late Paleozoic to Early Mesozoic, the geodynamic evolution of the Panthalassa margin is marked by strikingly synchronous changes in tectonic and magmatic setting and by the development of orogenic phases that occurred all along the margin.

Three main periods can be distinguished: (1) Early Permian times (280-260 Ma), (2) Late Permian to Middle Triassic times (260-230 Ma) and (3) Late Triassic times (230-200 Ma) (Fig. 2). (1) In Early Permian (275-260 Ma), the subduction flipped from east to

Acknowledgments

This research was funded by the SEDIT program in Paris (INSU, 2008 and 2009), the Labex OSUG@2020 in Grenoble, and the French Institut de Recherche pour le Développement (IRD). We thank Suzanne Kay, Veronica Oliveros and one anonymous reviewer for their helpful and constructive comments which help to greatly improve this manuscript.

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