See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/257820732 Double-saloon-door tectonics in the North Fiji Basin Article in Earth and Planetary Science Letters · July 2013 DOI: 10.1016/j.epsl.2013.05.041 CITATION READS 1 229 1 author: Keith Martin Looking for opportunities 29 PUBLICATIONS 726 CITATIONS SEE PROFILE All content following this page was uploaded by Keith Martin on 03 January 2017. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. 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Martin n Repsol, Al Fattan Plaza, PO Box 35700, Dubai, United Arab Emirates article info abstract Article history: Fiji Platform rotated counter clockwise from at least 10.2 Ma until 1.56 Ma, while Vanuatu Arc rotated Received 3 January 2013 clockwise from 12/10 Ma until the present. A revised model incorporating these opposite rotations Received in revised form explains the distribution of magnetic anomalies in the North Fiji Basin (NFB). The conjugate margin of 21 April 2013 southwest Fiji Platform is southeast Vanuatu Arc. Previous models which associate NW-oriented Accepted 22 May 2013 anomalies off southwest Fiji with similarly oriented anomalies northeast of Vanuatu Arc are therefore Editor: T.M. Harrison 1 1 Available online 14 June 2013 wrong. Secondly, these models propose a NW-oriented spreading ridge extending to 19 S, 177.5 E, almost 500 km southeast of the mapped extension of rifted island-arc crust on Vanuatu Arc. This creates an Keywords: unacceptable overlap with Fiji Platform in pre-rift reconstructions. Thirdly, anomalies off SW Fiji which tectonics are NW-oriented in their present-day position were oriented NNE during initial breakup. Rather than backarc aligning with NW-oriented anomalies in the western NFB, they are matched by NNE-oriented anomalies rotation propagation off SE Vanuatu Arc. With further rotation, these conjugate anomaly sets form a fan shape in the southern arc-perpendicular NFB. Fourthly, previous models which recognise a triple junction only from 3 Ma do not explain early arc-parallel WNW–ESE separation of Vanuatu Arc and Fiji Platform required by well-documented opposite rotations. NFB characteristics which match the double-saloon-door tectonic model include opposite rotations of island arc terranes, backarc seafloor spreading which is both arc-parallel and arc-perpendicular, and rifts propagating north, south, northeast and northwest. Features which do not match the double-saloon- door model include the North Fiji Fracture Zone and the West Fiji spreading centre. Both initiated post– 1.5 Ma, when Fiji Platform stopped rotating, and only one terrane, Vanuatu Arc, continued to rotate. The NFB developed via double saloon door tectonics from 12/10 Ma until 1.5 Ma, whereas post-1.5 Ma opening constitutes single saloon door rotation. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Secondly, NFB development has been ascribed to asymmetric opening, emphasising clockwise rotation of the Vanuatu Arc The North Fiji Basin (NFB) is one of the most active backarc (Schellart et al., 2002, 2006; Mann and Taira, 2004; Richards et al., basins in the world (Auzende et al., 1988a; Pelletier et al., 1993, 2011). This aligns with GPS data (Calmant et al., 1995, 2003 Taylor 2001; Ruellan and Lagabrielle, 2005). Active spreading over the et al., 1995) which confirm present-day CW rotation of Vanuatu Arc last 10–12 Ma (Fig. 1a and b) has been ascribed to the location on (Fig. 1b) where thrust earthquake epicentres are concentrated, the strike–slip boundary between the Pacific and Australian plates whereas strike–slip events occur south of the Fiji Platform on the (Hamburger and Isacks, 1988; Lafoy et al., 1990) or to unusually Hunter Fracture Zone (Hamburger and Isacks, 1988; Louat and hot underlying upper mantle (Lagabrielle et al., 1997). Models of Pelletier, 1989; Pelletier et al., 1998). NFB development (Auzende et al., 1988b, 1995a) show the south- However, this ignores paleomagnetic evidence (Fig. 2) which west margin of the Fiji Platform juxtaposed against the south- clearly demonstrates counter clockwise rotation of the Fiji Plat- eastern flank of the Vanuatu Arc in pre-breakup reconstructions form over the last 10 Ma, during most of the period of NFB opening dated at 10–12 Ma. However, these same models equate NW–SE- (James and Falvey, 1978; Malahoff et al., 1982a; Inokuchi et al., oriented magnetic anomalies off the southwest tip of Fiji Platform 1992; Taylor et al., 2000). with similarly oriented anomalies off the northeastern flank of the Here, I reconcile the paleomagnetic and GPS data by showing Vanuatu Arc (Auzende et al., 1988b, 1990). Despite this internal that the NFB opened via double saloon door tectonics over the inconsistency, these models have been widely quoted or adopted majority of its development period from 12/10 Ma until 1.5 Ma, (Schellart et al., 2002; Garel et al., 2003; Mann and Taira, 2004; whereas only a single saloon door rotation of Vanuatu Arc occurred Ruellan and Lagabrielle, 2005; Faccenna et al., 2010). after 1.5 Ma. Secondly, by incorporating the well documented CCW rotation of Fiji Platform (Fig. 2), I demonstrate that existing reconstruction models (Auzende et al., 1988b, 1995a; Ruellan and n Tel.: +971 506504357. Lagabrielle, 2005; Schellart et al., 2006; Faccenna et al., 2010)are E-mail address: [email protected] internally inconsistent, or incompatible with the progressive 0012-821X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2013.05.041 Author's personal copy 192 A.K. Martin / Earth and Planetary Science Letters 374 (2013) 191–203 Fig. 1. (a) The North Fiji Basin in its regional setting in the southwest Pacific Ocean (after Hall and Spakman, 2002; Mann and Taira, 2004; Schellart et al., 2006; Whattam et al., 2008). Light grey¼oceanic crust. Dark grey¼oceanic plateaus or island-arc crust. NZ¼New Zealand; PNG¼Papua New Guinea. CR¼Colville Ridge; FP¼Fiji Platform; KR¼Kermadec Ridge; LHR¼Lord Howe Rise; LR¼Lau Ridge; MBP¼Melanesian Border Plateau; NFB¼North Fiji Basin; NC¼New Caledonia; NR¼Norfolk Ridge; OJP¼Ontong Java Plateau; S¼Samoa; SCT¼San Cristobal Trench; SI¼Solomon Islands; TR¼Tonga Ridge; VA¼Vanuatu Arc; VT¼Vitiaz Trench. Black arrows show direction and rate in cm/yr of motion of the Pacific Plate relative to the Australian Plate (DeMets et al., 1994; Mann and Taira, 2004). (b) Main tectonic elements of the North Fiji Basin (NFB) (after Auzende et al., 1995a; Lagabrielle et al., 1996; Pelletier et al., 2001; Ruellan and Lagabrielle, 2005). White areas outlined in black¼island arc crust. Black¼Islands: A¼Aneityum; Ef¼Efate; Es¼Espirito Santo; M¼Malekula; Ta¼Tanna. Ridges: Ba, Bl and Br¼Balmoral, Bligh and Braemar (after Jarvis et al., 1994); D¼D'Entrecasteaux; WT¼West Torres Platform. Spreading Ridges: CSR¼Central; FSR¼Futuna; HH¼Hazel Holmes; SP¼South Pandora; Tr¼Tripartite; WFR¼West Fiji; Fracture Zones: EFZ¼Epi (after Greene and Collot, 1994; Raos and Crawford, 2004); HFZ¼Hunter; NFFZ¼North Fiji. Thin arrows show representative GPS convergence rates between the Vanuatu Arc and the Australian Plate (Calmant et al., 1995, 2003; Taylor et al., 1995; Wallace et al., 2005, 2009). In the Aneityum Tanna area rates are 116–124 mm/yr, in Efate 86–94 mm/yr, while in Espirito Santo and Malekula they are 17–43 mm/yr. Small dashed square shows the location of Fig. 10. 130 of magnetic lineations in the NFB are compatible with a model 120 incorporating opposite rotations (Fig. 3a–d).Thirdly,thereconstruc- tions are used to discuss NFB tectonic development, and specific 110 features such as rift propagation and arc-perpendicular seafloor 100 spreading. Fourthly, driving mechanisms for opposite rotations are discussed. Finally, features which do not match the double-saloon- 90 door model (opposite rotations) are discussed. 80 70 2. CCW and CW rotations of Fiji Platform, and Vanuatu Arc 60 respectively Degrees 50 Although James and Falvey (1978) thought the CCW Fiji Plat- 40 form rotation began 6 Ma ago, later work shows rotation began at least by 10 Ma (Malahoff et al., 1982a; Inokuchi et al., 1992; Taylor 30 et al., 2000). Linear regression through the data implies rotation 20 stopped at 1.46 Ma (Malahoff et al., 1982a; their Table 3 and Fig. 8) or at 2.7 Ma (Taylor et al., 2000; their Fig. 6). However their 10 Ma combined data (Fig. 2) suggest rotation of the Fiji Platform stopped 0 at 1.56 Ma, probably as it collided with the Lau Ridge. 01234567891011 Available paleomagnetic data indicate a CW rotation of Vanuatu Fig. 2. Compilation of paleomagnetic rotations for Fiji platform (Malahoff et al., Arc of 28–301 from 6 Ma or 521 from 4 Ma (Falvey, 1978; Musgrave 1982a, blue diamonds; Taylor et al., 2000, magenta squares).