Gondwana Pangea assembly and dispersal

The assembly of Gondwana began immediately following the break-up of Rodinia in Late Proterozoic times. According to the SWEAT hypothesis (Section 11.5.3) West Gondwana formed when many small ocean basins that surrounded the African and South American cratons closed during the opening of the proto-Pacific Ocean, creating the Pan-African orogens (Fig. 11.19b). Subsequent closure of the Mozambique Ocean resulted in the collision and amalgamation of West Gondwana with the blocks of East Gondwana. This amalgamation may have created a short-lived Early Cambrian supercontinent called Pannotia. The existence of this supercontinent is dependent on the time of rifting between Laurentia and Gondwana (Cawood et al., 2001). Models of Pannotia (Fig. 11.23a) are based mostly on geologic evidence that Laurentia and Gondwana were attached

West Gondwana Proterozoic
Fig. 11.22 Reconstruction of the postulated Early-Middle Proterozoic supercontinent Columbia (after Zhao et al., 2002, with permission from Elsevier). M, Madagascar. Early Proterozoic orogens (2.1-1.8 Ga) are identified in Fig. 11.12.
Gondawana Mozambique Belt

Fig. 11.23 Postulated reconstructions of (a) Pannotia at ~545 Ma and (b) the rifting of Laurentia and Gondwana at ~465 Ma emphasizing the paleogeography of Laurentia relative to Gondwana (after Dalziel, 1997, with permission from the Geological Society of America). Crosses with 95% confidence circles shown in (a) with a dashed line and a dashed-dotted line indicate paleomagnetic poles for Laurentia and Gondwana, respectively. Horizontal lines in (a) denote limit of the Mozambique orogenic belt; thick solid black line marks the location of a Laurentia-Gondwana rift. In (b) paleomagnetic poles are for Laurentia + Baltica + Siberia + Avalonia (cross with dashed confidence circle) and Gondwana (cross with dashed-dotted confidence circle). Cuyania (CT) has accreted onto the Gondwana margin. Abbreviations: C, Congo; K, Kalahari; WA, West Africa; AM, Amazonia; RP, Río de la Plata; SF, Sao Francisco; S, Siberia; B, Baltica; TxP, the hypothetical Texas Plateau; F, Famatina arc; E, Exploits arc.

Fig. 11.23 Postulated reconstructions of (a) Pannotia at ~545 Ma and (b) the rifting of Laurentia and Gondwana at ~465 Ma emphasizing the paleogeography of Laurentia relative to Gondwana (after Dalziel, 1997, with permission from the Geological Society of America). Crosses with 95% confidence circles shown in (a) with a dashed line and a dashed-dotted line indicate paleomagnetic poles for Laurentia and Gondwana, respectively. Horizontal lines in (a) denote limit of the Mozambique orogenic belt; thick solid black line marks the location of a Laurentia-Gondwana rift. In (b) paleomagnetic poles are for Laurentia + Baltica + Siberia + Avalonia (cross with dashed confidence circle) and Gondwana (cross with dashed-dotted confidence circle). Cuyania (CT) has accreted onto the Gondwana margin. Abbreviations: C, Congo; K, Kalahari; WA, West Africa; AM, Amazonia; RP, Río de la Plata; SF, Sao Francisco; S, Siberia; B, Baltica; TxP, the hypothetical Texas Plateau; F, Famatina arc; E, Exploits arc.

or in close proximity at the end of the Late Proterozoic (Dalziel, 1997). However, the paleomagnetic poles for these two landmasses do not overlap, suggesting that an alternative configuration where Laurentia is separated from Gondwana at this time also is possible (Meert & Torsvik, 2003).

Most models suggest that the break-up of Pannotia began with the latest Proterozoic or Early Cambrian opening of the Iapetus Ocean as Laurentia rifted away from South America and Baltica (Figs 11.19b, 11.23b). Subduction zones subsequently formed along the Gondwana and Laurentia margins of Iapetus, creating a series of volcanic arcs, extensional backarc basins, and rifted continental fragments. As the ocean closed this complex assemblage of terranes accreted onto the margins of both Laurentia and Gondwana. The provenance of these terranes provides a degree of control on the relative longitudes and paleogeography of these two continents prior to the Permo-Carboniferous assembly of Pangea (Dalziel, 1997).

The Early Paleozoic accreted terranes of Laurentia and Gondwana are classified into groups according to whether they are native or exotic to their adjacent cratons (Keppie & Ramos, 1999; Cawood, 2005). Those native to Laurentia include the Notre Dame-Shelburne Falls (Taconic) and Lough-Nafooey volcanic arcs (Figs 10.34, 11.24a), which formed near and accreted onto Laurentia during Early-Middle Ordovi-cian times. These collisions were part of the Taconic Orogeny in the Appalachians (Karabinos et al., 1998), the Grampian Orogeny in the British Isles, and the Finnmarkian Orogeny in Scandinavia. During the same period, the Famatina arc terrane (Fig. 11.23b), of Gondwana affinity, formed near and accreted onto the western margin of South America (Conti et al., 1996).

Terranes exotic to Laurentia include Avalonia, Meguma, Carolina, and Cadomia (Fig. 11.24a). These

Fig. 11.24 Postulated Paleozoic plate reconstructions for (a) 490 Ma, (b) 440 Ma, and (c) 420 Ma emphasizing the paleogeography of terranes derived from northern Gondwana and the opening of the Rheic Ocean (images provided by G.M. Stampfli and modified from von Raumer et al., 2003, and Stampfli & Borel, 2002, with permission from Elsevier). Interpretations incorporate the dynamics of hypothesized convergent, divergent and transform plate boundaries. Labeled terranes in (a) are: Mg, Meguma; Cm, Cadomia; Ib, Iberia; Cr, Carolina.

Spreading Center Transform Subduction
~490 Ma Transform and spreading center
Greenland Subduction Zone Map

~440 Ma Transform and spreading center

Subduction zone Suture zone

~440 Ma Transform and spreading center

Suture Zone
Subduction zone Suture zone

ASIATIC ,

~420 Ma Transform and spreading center and other terranes rifted from northwestern Gondwana in the Early Ordovician and later accreted onto the Lau-rentian margin, forming part of the Silurian-Devonian Acadian and Salinic orogens in the northern Appalachians and the Caledonides of Baltica and Greenland (Figs 11.24c, 11.25). Cuyania, an exotic terrane located in present day Argentina (Fig. 11.23b), rifted from southern Laurentia during Early Cambrian times and later accreted onto the Gondwana margin (Dalziel, 1997). These tectonic exchanges suggest that at least two different plate regimes existed in eastern and western Iapetus during the Paleozoic with subduction zones forming along parts of both Gondwana and Laurentia (Fig. 11.24a). Although the geometry of the plate boundaries is highly speculative, the interpretation of distinctive plate regimes explains the piecemeal growth of both continents by terrane accretion prior to the assembly of Pangea.

The rifting of the Avalonia terranes from Gondwana in the Late Cambrian and Early Ordovician led to the opening of the Rheic Ocean between the Gondwana mainland and the offshore crustal fragments (Fig. 11.24a,b). After the closure of Iapetus and the accretion ofAvalonia, the Rheic Ocean continued to exist between Laurentia and Gondwana, although its width is uncertain (Fig. 11.24c). During these times a new series of arc terranes rifted from the Gondwana margin, resulting in the opening of the Paleotethys Ocean (Fig. 11.26a). The opening of Paleotethys and the closure of the Rheic Ocean eventually resulted in the accretion ofthese Gond-

Moesian Tectonic Plate

Fig. 11.25 Late Paleozoic reconstruction showing the Silurian-Devonian Appalachian (Acadian and Salinic)-Caledonian orogens (after Keller & Hatcher, 1999, with permission from Elsevier). TTZ is the Teisseyre-Tornquist zone, representing a major crustal boundary between Baltica and southern Europe.

wana-derived terranes onto Laurentia followed by a continent-continent collision between Laurussia and Gondwana (Fig. 11.26b). This latter collision produced the Permo-Carboniferous Alleghenian and Variscan orog-

Pangea Gondwana

Spreading center and transform fault v v Subduction zone -?—f" Suture zone

Fig. 11.25 Late Paleozoic reconstruction showing the Silurian-Devonian Appalachian (Acadian and Salinic)-Caledonian orogens (after Keller & Hatcher, 1999, with permission from Elsevier). TTZ is the Teisseyre-Tornquist zone, representing a major crustal boundary between Baltica and southern Europe.

Fig. 11.26 Postulated Paleozoic plate reconstructions for (a) 400 Ma and (b) 300 Ma (images provided by G.M. Stampfli and modified from Stampfli & Borel, 2002, with permission from Elsevier). In (a) The Rheic Ocean closes as Paleotethys opens. In (b) Gondwana has collided with Laurussia creating the European Variscides and Alleghenian Orogen.

Tornquist Zone
Fig. 11.27 Reconstruction of Pangea at 250 Ma (after Torsvik, 2003, with permission from Science 300, 1379-81, with permission from the AAAS). Major cratons are shown.

enies in North America, Africa, and southwest Europe. Collisions in Asia, including the suturing of Baltica and Siberia to form the Ural Orogen at ~280 Ma, resulted in the final assembly of Pangea. The supercontinent at the height of its extent at ~250 Ma is shown in Fig. 11.27.

Like its assembly, the fragmentation of Pangea was heterogeneous. Break-up began in the mid-Jurassic with the rifting of Lhasa and West Burma from Gondwana and the opening of the central Atlantic shortly after 180 Ma (Lawver et al., 2003). Magnetic anomalies indicate that by 135 Ma the southern Atlantic had started to open. Rifting between North America and Europe began during the interval 140-120 Ma. Africa and Ant arctica began to separate by 150 Ma. Australia also began to rift from Antarctic by 95 Ma with India separating from Antarctica at about the same time. These data indicate that the majority of Pangea break-up occurred during the interval 150-95 Ma. Small fragments of continental crust such as Baja California and Arabia continue to be rifted from the continental remnants of Pangea. As with the older supercontinents, the break-up of Pangea was accompanied by the closure of oceans, such as Paleotethys and Neotethys (Fig. 11.27), and by collisions, including those that occur presently in southern Asia (Fig. 10.13), southern Europe, and Indonesia (Fig. 10.28).

The mechanism of plate tectonics

Gondwana Assembly

Was this article helpful?

0 0
Boating Secrets Uncovered

Boating Secrets Uncovered

If you're wanting to learn about boating. Then this may be the most important letter you'll ever read! You Are Going To Get An In-Depth Look At One Of The Most Remarkable Boating Guides There Is Available On The Market Today. It doesn't matter if you are just for the first time looking into going boating, this boating guide will get you on the right track to a fun filled experience.

Get My Free Ebook


Post a comment