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Rodinia


Abstract

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Keywords: tectonics, continental drift, paleogeography, palaeogeography, Rodinia

Introduction

The protracted acceptance of continental drift was one of the great scientific sagas of the twentieth century. Today, although many details of the causal machanisms remain obscure, it is almost universally accepted that the continents ride across the face of the earth on tectonic plates which have been in constant movement since the formation of the crust. The continents we recognise today have not always existed: great blocks of crust have united in many configurations over the planet's long history. And, more than once, all (or at least the great majority) of the earth's crust has been united into a single supercontinent.

The most recent such amalgamation was Pangaea, which is relatively well known and about which the interested reader will easily find much information elsewhere. An earlier massing into a single supercontinent during the Precambrian, "remains shrouded in mystery" (Torsvik 2003, p. 1379).

 
 

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Further Reading

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Discovery

The existence of a Precambrian supercontinent was proposed in the 1970s, largely motivated by the evidence of contemporaneous (1.3 to 1.0 Ga) "Grenville" mountain belts on what are today different continents, and broadly supported by paleomagnetic studies. Various names were offered, including Ur-Pangea, Proto-Pangea and variations (McMenamin 1998, p. 176), but most authorities had already settled on Rodinia by the early 1990s (e.g. Dalziel 1991; Moores 1991; Hoffman 1991 [® sidebar]). Also check Rogers 1996.
Mark McMenamin claims that he and Dianna McMenamin were the first coin this name, in their 1990 publication Emergence of Animals, p. 95 (McMenamin 1998, p. 176).
Most of the early models sought to align the Grenville-aged mountain belts, with Laurentia forming the core of the continent, flanked by Australia and East Antarctica on the west, and Baltica and Amazonia on the east (fig. 1).

Even today, however, "elucidation of its amalgamation, continental makeup, and fragmentation is hampered by the fact that at any given time, the latitudes for only a few continents are known" (Torsvik 2003, pp. 1380-1381).

Fig. 1: A conventional reconstruction of Rodinia at 750 Ma (after Torsvik 2003).

Formation

Rodinia began forming ~1,300 Ma from the amalgamation of three or four pre-existing continents, in an event known as the Grenville Orogeny, consolidating perhaps 1,100 to 1,000 Ma.
The Grenville Province is a terrane of metamorphism and deformation running from Labrador to Texas, once comprising the southern coast of Laurentia. Ar/Ar dating of gabbros and basalts from the Nova Floresta Formation in western Brazil, parts of the Amazon craton which collided with the region that is now Texas during the formation of Rodinia (Llano Uplift), have yielded dates around 1,200 Ma (Tohver et al. 2002).

Fig. 2: A recent reconstruction of Rodinia at 750 Ma based on Hartz & Torsvik 2002 (after Torsvik 2003).

Torsvik p. 1380: "Large uncertainties concern the position of Siberia. Early Rodinia reconstructions show Siberia north of Laurentia [fig. 1] whereas others place Siberia along the western margin of Laurentia. Yet another extreme shows Siberia west [sic] of Baltica [fig. 2]. The positions of Amazonia-Rio Plata and Congo-Kalahari also differ substantially between the old and new models..."

Dissolution

Early models assumed that Rodinia remained more or less static from its formation until breaking up, perhaps beginning ~700 Ma, but protracted over many millions of years, into three major blocks: West Gondwana, East Gondwana, and Laurasia (e.g. Rogers 1996).
Australia-East Antarctica rifted away from the western margin of Laurentia first, with other continents rifting away subsequently, and in the case of Baltica and Amazonia, perhaps as late as 600 to 550 Ma, opening the Iapetus Ocean between them. Subsequently - perhaps ~540 Ma - West and East Gondwana collided and merged in the mountain-building event known as the Pan-African Orogeny.
Newer models postulate Rodinia disintegrating before 750 million years ago, most likely between 850 and 800 Ma (Torsvik 2003, p. 1380). Torsvik p. 1380: "Disruption likely began with the opening of an ocean between western Laurentia and Australia-East Antarctica.... The East Gondwana landmass could not have been a coherent block 750 million years ago [Torsvik et al. 2001; Meert 2003], and India-Madagascar-Seychelles must have been located west of Australia. recent maps [Hartz & Torsvik 2002] also show Baltica geographically inverted relative to Laurentia [fig. 2].

Stratigraphy

Type Section/Sections

 

Lower Boundary

Upper Boundary

Chronology

Paleogeography

Major Tectonic Events

Land and Sea

Climate

Paleontology

General Characteristics

Lagerstätten

Major Evolutionary Events

Major Taxa

References

Dalziel, I.W.D. 1991: Geology 19: 598.

Hartz, Ebbe H.; Torsvik, Trond H. 2002: Baltica upside down: A new plate tectonic model for Rodinia and the Iapetus Ocean. Geology 30: 255-258.

Hoffman, P.F. 1991: Science 252: 1409.

Meert, Joseph G. 2003: A synopsis of events related to the assembly of eastern Gondwana. Tectonophysics 362: 1-40.

Moores, E.M. 1991: Southwest U.S.-East Antarctic (SWEAT) connection: A hypothesis. Geology 19: 425-428.

Rogers, J.J.W. 1996: A history of the continents in the past three billion years. Jl. Geol. 104: 91-107.

Tohver, Eric; van der Pluijm, B.A.; Van der Voo, R.; Rizzotto, G.; Scandolara, J.E. 2002: Paleogeography of the Amazon craton at 1.2 Ga: early Grenvillian collision with the Llano segment of Laurentia. Earth and Planetary Science Letters 199: 185-200.

Torsvik, Trond H. 2003: The Rodinia jigsaw puzzle. Science 300: 1379-1381.

Torsvik, T.H. et al. 2001: Precambrian Research 108: 319.


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