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The Tectonic History of the Tasman Sea a Puzzle with 13 Pieces

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The Tectonic History of the Tasman Sea a Puzzle with 13 Pieces JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 103, NO. B6, PAGES 12,413-12,433, JUNE 10, 1998 The tectonic history of the Tasman Sea: A puzzle with 13 pieces CarmenGaina, • Dietmar R. Mtiller,•Jean-Yves Royer,: Joann Stock, 3 JeanneHardebeck, 3 and Phil Symonds4 Abstract. We presenta new model for the tectonicevolution of the TasmanSea basedon dense satellitealtimetry data and a new shipboarddata set. We utilized a combinedset of revised magneticanomaly and fracture zone interpretations to calculaterelative motions and their uncertaintiesbetween the Australianand the Lord Howe Rise platesfrom 73.6 Ma to 52 Ma when spreadingceased. From chron31 (67.7 Ma) to chron29 (64.0 Ma) the modelimplies transpressionbetween the Chesterfieldand the Marion plateaus, followed by strike-slipmotion. This transpressionmay havebeen responsible for the formationof the CapricornBasin south of the Marion Plateau. Anothermajor tectonic event took place at chron27 (61.2 Ma), whena counterclockwisechange in spreadingdirection occurred, contemporaneous with a similarevent in the southwestPacific Ocean. The earlyopening of theTasman Sea cannot be modeledby a simple two-platesystem because (1) riftingin thisbasin propagated from southto northin severalstages and(2) severalrifts failed. We identified13 continentalblocks which acted as microplates between 90 Ma and64 Ma. Our modelis constrainedby tectoniclineaments visible in the gravityanomaly grid and interpretedas strike-slipfaults, by magneticanomaly, bathymetry and seismicdata, and in caseof the SouthTasman Rise, by the ageand affinity of dredgedrocks. By combiningall this informationwe derivedfinite rotations that describe the dispersal of thesetectonic elements during the early openingof the TasmanSea. 1. Introduction anomaly24) for the TasmanSea. They describedthe opening of the basin in terms of a two-plate spreading system but About two decadesago the opening of the TasmanSea was consideredthe possibility of a subductioninterval to account modeled by several authors as a simple two-plate spreading for the truncated pattern of magnetic anomalies near SE system,active betweenchron 33old (80 Ma) and post-chron24 Australia. After calculating finite rotations based on (52 Ma). New geophysicaldata, however,offer an opportunity reidentified magnetic anomalies, Weissel and Hayes [1977] for reconstructingthe tectonic history of the Tasman Sea in concludedthat the assumptionof an episodeof subductionof muchmore detail than previously possible. We present a new Tasman basin crust at the east Australian margin is not tectonic model based on gravity anomaly data derived from necessary, because an extension of the two plate model satellitealtimetry and on both existingand new magneticdata, describedthe evolutionof mostof the basinquite well. as well as on seismicand geologicaldata. Shaw [1979] was the first author to interpret magnetic The Tasman Sea is an ocean basin boundedto the west by anomalies north of 30øS in the Tasman Sea based on new continental Australia, to the east by the Lord Howe magnetic data. Following Ringis' [1972] idea that initial Rise/ChallengerPlateau and New Zealand,and to the southby a rifting had takenplace in the Lord Howe and Middleton basins major discordancethat separatesit from younger oceanic crust (Figure 1), Shaw [1979] attempted to identify magnetic generated at the Southeast Indian Ridge and the extinct anomaliesin thesebasins. He arguedthat the northernTasman MacquarieRidge spreadingcenter (Figure 1). Its northernpart Sea morphologycould be explainedonly by strikeslip motion contains an elongated segment of continental crust, the and not a pull-apartmechanism as suggestedby Weissel and Dampier Ridge, separatedfrom the Lord Howe Rise by two Hayes[1977]. Stockand Molnar [1982] interpretedmagnetic small basins: the Lord Howe and the Middleton basins. anomalyand fracturezone locations in the SW Pacific region, Hayes and Ringis [1973] identified for the first time a and computednew rotations for anomalies 28 and 32 in the complete magnetic anomaly set (from anomaly 330 to TasmanSea, including partial uncertaintyrotations. Another tectonic model for the central and southern Tasman Sea, based • Departmentof Geologyand Geophysiscs,University of Sydney, New South Wales, Australia. on a revisedmagnetic data set and the gravity anomaly grid 2 Unit6 Mixte de Recherche6526, G6osciencesAzur, Villefranche publishedby Sandwelland Smith[1992] hasbeen proposed by Sur Mer, France. Rollet [1994]. Rollet [1994] used the inversion method 3 SeismologicalLaboratory, California Institute of Technology, developedby Royer and Chang [1991] for computingfinite Pasadena. 4 AustralianGeological Survey Organisation, Canberra, Australia. rotations,and the resultsare very similar to Shaw's [1979]. Copyright1998 by the AmericanGeophysical Union 2. Magnetic Data Papernumber 98JB00386. In this studywe compiledmagnetic anomaly crossings from 0148-0227/98 JB-00386509.00 new ship data (HMAS Cook (1985-1989), R/V Melville 12,413 12,414 GAINA ET AL.: TECTONIC HISTORY OF THE TASMAN SEA l TASMAN SEA magneticanomaly • 24o, 28y, 33y, 25 øS • 25y c• 260, 31y, 34y o 27o, 32y • 29y v 30y 30'S 35'S 40'S 45'S • . 50øSl"_ I I I I I I I I I I I ll 150øE 155•E 160øE 165•E 170øE Figure 1. Tasman Sea, magnetic anomalies plotted along selectedship tracks. Shadedareas indicate continental crust; AUS, Australia;TAS, Tasmania;LHR, Lord Howe Rise; DR, Dampier Ridge; STR, South TasmanRise; GSM, Gilbert SeamountComplex; NZ, New Zealand;Chest. P1, ChesterfieldPlateau; Chall. P1, ChallengerPlateau; Bellona Tr, Bellona Trough;Lord Howe, Lord Howe basin; Middleton, Middleton basin; ETR, East Tasman Plateau; Marion P1, Marion Plateau; dark grey line represents extinct ridge axis. Bold profilesare presentedin Figures3 and 10. GAINAET AL.:TECTONIC HISTORY OF THE TASMAN SEA 12,415 sw ridgeextinctaxis bmr14 /•_^ )•,,•/• I I .I I I I I , I I • , , ' ' , ; ' ; •; • , mv9512 ,',' I • • : ' ; ' • '" II ' ' ' I I I I ' at941 r . ß ' • ' , . I I ! ! , ,, - ' , , I , ,' ,, synthetic • ,t ,,' ,I ,I .,, :{l I a, . , profile • '.' , , ' •. • , , , ! ' I ' { , I ' I I I I • I , , , , , , , , , , , , , • • , • , , , , • ', 34y 33o 33 32 31 30 29 28 27 26 25 • • 25 26 27 •29 30 31 32 33 330 •y 4m•yr q, . 22mm/yr • 16•yr • 20•yr _,.4mm/yr h•f spread•g ute 83 79,1 73.6 71.0 67.7 64.0 61.2 55.9 53.3 I I I I I I I I I Ma Figure 2. Selectedmagnetic anomaly profiles of theTasman Sea compared with synthetic magnetic anomalies(see locations in Figure 1). Thesynthetic profiles are based on the geomagnetic timescale of Cande andKent [1995], a depthto the upper surface of themagnetized layer of 3 km,a thicknessof the magnetized layerof 1.5km and an azimuth of 150ø. Thepresent inclination and declination ofthe magnetic field were calculatedfrom the IGRF90 reference field and the paleoinclination and paleodeclination were calculated based onthe position of thepaleomagnetic polefor the Australian plate at 52 Ma[from Irving and Irving, 1982]. Australia'slatitudinal position did not change substantially while the Tasman Sea was opening; hence we foundthat it makeslittle difference for the phase shift of syntheticmagnetic anomalies whether we use a late Cretaceousor an earlyTertiary paleomagnetic pole. (1995), N/O L'Atalante(1994), and R/V MauriceEwing wherewe were able to identify a considerablenumber of (1996)) andreinterpreted previously existing data (Figure 1). magneticanomalies. However,a detaileddiscussion of Using the Candeand Kent [1995] reversaltimescale, we spreadingasymmetry is beyondthe scopeof this paper. identifiedeither young or oldends of magneticchrons (Figure Specialattention has been paid to the northernpart of the 2), unlikeprevious authors who chose the centerof magnetic TasmanSea where volcanic activity has partly obliterated anomalies[Weissel and Hayes,1977; Shaw, 1979] or only the magneticlineations on the seafloor;we succeededin olderends [Rollet, 1994]. Anomalieson the westernflank lie identifyingmagnetic anomalies in the northernmostTasman fartherfrom the ridgethan correspondinganomalies on the Sea but not in the Lord Howe or Middleton basins, which are easternflank. Asymmetryin crustal accretionoccurred likely to be underlainby extendedcontinental crust. We especiallybetween chron 270 andchron 33y. This observation identified anomalies330 and 34y (young) in the central is mostlybased on magnetic data from the central Tasman Sea, Tasman Sea. However, the scarcity of data hinder the 12,416 GAINA ET AL.: TECTONIC HISTORY OFTHE TASMAN SEA interpretation of Late Cretaceousanomalies in the southern The selectedfracture zone limb displaysthe samepattern as Tasman Sea. the other fracturezone in the TasmanSea (i.e., a changein spreadingdirection shortly before the ridge becameextinct; 3. Fracture Zone Data Figure3). As the morphology of this fracturezone resembles the Atlantic type (a central valley boundedby a high wall on Images of the marine gravity field [Sandwelland Smith, the older side), we usedthe troughsin the gravity anomaly as 1997] from satellite altimetry allow improved interpretations the actual location of the fracture zone. To better constrain of fracture zones and other tectonic features (an extinct reconstructionsfor chrons25y and 240, which imply a change spreadingridge, continent ocean boundary, V-shaped features). in the direction of spreading,we includedadditional points The generalNNE trendof the fracturezones interpretedfrom from other relevantfracture zone segments. densesatellite gravity datadiffers from previouslyinterpreted fracturezones
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