Wise, S. W., Jr., Schlich, R., et al., 1992 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 120 50. JURASSIC TO EOCENE PLATE TECTONIC RECONSTRUCTIONS IN THE KERGUELEN PLATEAU REGION1 Jean-Yves Royer2 and Millard F. Coffin3 ABSTRACT We present a series of preliminary reconstructions for the Kerguelen Plateau region from the Late Jurassic to the Eocene that summarize and review the outstanding questions about its plate tectonic evolution. The development of the Indian and adjacent Southern oceans began in Middle to Late Jurassic time with the breakup of Gondwana. Marine magnetic anomalies and limited Deep Sea Drilling Project and Ocean Drilling Program core samples have been used to date the oceanic crust. Fracture zone trends interpreted from satellite (SEASAT and GEOSAT) altimetry, and marine seismic, gravity, and magnetic data have been combined with crustal dates to produce kinematic models of the plates through time. Between the Jurassic and the Late Cretaceous, time controls on the plate tectonic evolution of the region are few. Mesozoic marine magnetic anomalies off the shore of East Africa, Antarctica, and Western Australia document plate motions during the interval; however, extensive areas of oceanic crust from which no anomalies have been identified, including that created during the Cretaceous Long Normal Polarity Interval, and a dearth of fracture zones prevent detailed links with the much better defined plate kinematic synthesis for the past 84 m.y. The Kerguelen Plateau/Broken Ridge complex was emplaced at ~ 110 Ma in a region flanked by Greater India, Australia, and Antarctica. Between then and —43 Ma, when seafloor spreading between the Kerguelen Plateau and Broken Ridge began, our model includes transform motions between the northern and southern sectors of the Kerguelen Plateau. INTRODUCTION Gondwana included Africa. In the second phase, in Early Cretaceous time, East and West Gondwana dispersed and The plate kinematic history of the Indian and adjacent reorganized through the transfer of crustal blocks. Madagas- Southern oceans has been analyzed and described since car/Seychelles/Greater India separated from Australia/Antarc- shortly after the advent of the plate tectonics paradigm. tica. Later on, relative motion between Africa and Madagas- Marine magnetic (McKenzie and Sclater, 1971; Norton and car/Seychelles/Greater India ceased. The third phase, starting Sclater, 1979) and SEASAT/GEOSAT radar altimeter (Royer in mid-Cretaceous time, was marked by a further disintegra- and Sandwell, 1989) data have been used to show that the tion and reorganization of the Gondwana fragments into four oceans formed by a series of seafloor-spreading episodes and plates: Seychelles/Greater India and Africa/Madagascar broke differing plate geometries (Figs. 1 and 2). Although the Cen- up, as did Australia (including Broken Ridge and the Northern ozoic evolution of the ocean basins is fairly well known, the Kerguelen Plateau) and Antarctica (including the Southern Mesozoic history is more problematic because of the Creta- Kerguelen Plateau). In the fourth phase, the Seychelles trans- ceous Long Normal Polarity Interval and the scarcity of ferred from the Indian to the African plate in Paleocene time, marine magnetic data from areas of suspected older crust. Our and the number of plates remained at four. In the fifth phase, intent is to summarize the plate kinematic evolution of the India and Australia joined to become one plate, leaving a total ocean basins surrounding the Kerguelen Plateau/Broken of three. At the same time, the northern sector of the Ridge complex and to outline the major questions about the Kerguelen Plateau was transferred from the Indo-Australian tectonic evolution of this region between the Late Jurassic and Plate to the Antarctic Plate as Broken Ridge and the Ker- the middle Eocene. guelen Plateau were separated by the westward-propagating Southeast Indian Ridge in Eocene time. RECONSTRUCTIONS In the following, we describe briefly these salient events Gondwana began to break up and disperse in Mesozoic (using the time scales of Berggren et al., 1985; Kent and time. In some cases, rifting preceded breakup by many tens of Gradstein, 1985; Handschumacher et al., 1988) in the tectonic millions of years, and extensive volcanism and associated development of the southern Indian and adjacent Southern intrusions commonly accompanied the rifting (e.g., Hinz, oceans. The 110-Ma and older reconstructions, based on 1981; Cox, 1988; Mahoney, 1988; Davies et al., 1989). Jurassic published data, are considered qualitative and provisional, through Eocene seafloor spreading in the Indian Ocean region pending a thorough analysis of all pertinent geophysical and occurred in five major phases (Table 1). During the first, in geological data. No satisfactory model has yet been proposed Late Jurassic time, Gondwana rifted into two major litho- for the early opening of the Indian Ocean. Norton and spheric plates, East and West Gondwana. In the Indian Ocean Sclater's (1979) model was based on very sparse data. Ségou- sector, East Gondwana included Madagascar, the Seychelles, fin and Patriat (1980) focused on the relative motions of the Greater India, Sri Lanka, Australia, and Antarctica; West African, Antarctic, and Madagascan plates. Bergh (1987) proposed different solutions for the Antarctic/Africa relative motions, whereas Powell et al. (1988) proposed a model limited to the Indian/Antarctic/Australian plate system. In- 1 Wise, S. W., Jr., Schlich, R., et al., 1992. Proc. ODP, Sci. Results, 120: College Station, TX (Ocean Drilling Program). compatibilities among these different models highlight the 2 Laboratoire de Géodynamique sous-marine—O.O.V., B.P. 48, 06230 necessity of considering all of the relevant plates simultane- Villefranche sur mer, France. ously. Some of the ideas used in our model were developed by 917 J.-Y. ROYER, M. F. COFFIN Bathymetric Chart of the Indian Ocean 2000 and 4000 meters sobaths (redrawn after Irte GEBCO Chans series) 30S 60S 0 30E 60E 90E 120E 150E Figure 1. Bathymetric chart of the Indian Ocean (2000- and 4000-m isobaths) after Royer et al. (1989). Lawver et al. (in press). We used the pre-breakup configura- age has been identified in the Indian or adjacent Southern tion for Gondwana of Lawver and Scotese (1987) as a starting oceans. In the region that was to become the Indian Ocean, point at 165 Ma. The relative position of Madagascar relative the initial rifts separated West Gondwana, which included to Africa at 130 Ma (M10) and 119 Ma (M0) are based on Africa, from East Gondwana, which included Madagascar, Ségoufin and Patriafs (1980) model. The relative motions of the Seychelles, Greater India, Australia, and Antarctica. East Australia and Antarctica between 165 and 43 Ma are from and West Gondwana may have undergone an episode of Royer and Sandwell (1989). For the pre-MO reconstructions of stretching at nearly right angles to the subsequent spreading Africa and Antarctica, we matched Mesozoic lineations in the direction (Coffin and Rabinowitz, 1987, 1988; Reeves et al., Mozambique Channel with those off Dronning Maud Land in 1987). The pre-rift fit of Gondwana components is poorly Antarctica. The rates and directions of spreading in the Perth constrained because of a scarcity of information on continen- Basin were used to constrain the India/Australia relative tal extension. motions. Other geometrical constraints (e.g., no overlap be- Continental extension and limited seafloor spreading (Fig. tween India and Madagascar) were also taken into account. 3) began to occur between West and East Gondwana (Rab- The 84-Ma and younger reconstructions are based largely on inowitz et al., 1983; Coffin and Rabinowitz, 1987), and be- the more quantitative plate kinematic analysis of Royer et al. tween northwest Australia (East Gondwana) and its unidenti- (1988) and Royer and Sandwell (1989). We interpreted a fied conjugate ("Argo" land mass of Powell et al., 1988). The transform boundary between the northern and southern prov- overall plate configuration at the time of breakup is uncertain inces of the Kerguelen Plateau along the 77°E Graben (Coffin because of the poorly defined continent/ocean boundaries of et al., in prep.). The rotation parameters determined in this the Gondwana fragments. study are provided in the figure captions. The age of the oldest oceanic crust in the southern Indian Ocean is not known. Larson (1975) estimated that oceanic BREAKUP CONFIGURATION crust began forming off northwest Australia at the time of Although rifting, associated rift volcanism and intrusion, magnetic lineation M25 (157 Ma) or earlier; with additional and probable continental extension occurred between East data Fullerton et al. (1989) identified lineation M26 (158 Ma). and West Gondwana before 200 Ma, at least as early as However, drilling on magnetic lineation M26 off northwest Permo-Carboniferous time (e.g., review in Coffin and Rab- Australia provided a date of Early Cretaceous (Gradstein, inowitz, 1988), no oceanic crust of Early Jurassic or greater Ludden, et al., 1990), or ~20 m.y. younger than the accepted 918 PLATE TECTONIC RECONSTRUCTIONS 30S 60S I I I I I I 0 30E 60E 150E Figure 2. Tectonic fabric chart of the Indian Ocean (from Royer et al Table 1. Indian Ocean spreading chronology. 165 Ma M10/M0 - 132/119 110 Ma C34 - 84 Ma C28 - 64 Ma C18 - 43 Ma Ma Africa Africa Africa Africa Africa Africa Madagascar Madagascar Madagascar Madagascar Madagascar Madagascar Seychelles Seychelles Seychelles Seychelles Seychelles Greater India Greater India Seychelles Greater India India India India Australia Australia Antarctica Australia Australia Australia Australia Broken Ridge Antarctica Broken Ridge Broken Ridge Broken Ridge Kerguelen Plateau northern Kerguelen Pl. northern Kerguelen PL Antarctica Antarctica Antarctica Antarctica northern Kerguelen Pl. southern Kerguelen Pl. southern Kerguelen Pl. southern Kerguelen Pl. Note: Rippled lines indicate uncertain plate configurations. 919 J.-Y. ROYER, M. F. COFFIN Figure 3. Plate tectonic reconstruction at 165 Ma. Seafloor spreading has begun between East and West Gondwana, and off northwest Australia.