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Hikurangi Plateau: Crustal Structure, Rifted Formation, and Gondwana Subduction History

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Hikurangi Plateau: Crustal Structure, Rifted Formation, and Gondwana Subduction History Article Geochemistry 3 Volume 9, Number 7 Geophysics 3 July 2008 Q07004, doi:10.1029/2007GC001855 GeosystemsG G ISSN: 1525-2027 AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Published by AGU and the Geochemical Society Click Here for Full Article Hikurangi Plateau: Crustal structure, rifted formation, and Gondwana subduction history Bryan Davy Institute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt, New Zealand ([email protected]) Kaj Hoernle IFM-GEOMAR, Wischhofstraße 1-3, D-24148 Kiel, Germany Reinhard Werner Tethys Geoconsulting GmbH, Wischhofstraße 1-3, D-24148 Kiel, Germany [1] Seismic reflection profiles across the Hikurangi Plateau Large Igneous Province and adjacent margins reveal the faulted volcanic basement and overlying Mesozoic-Cenozoic sedimentary units as well as the structure of the paleoconvergent Gondwana margin at the southern plateau limit. The Hikurangi Plateau crust can be traced 50–100 km southward beneath the Chatham Rise where subduction cessation timing and geometry are interpreted to be variable along the margin. A model fit of the Hikurangi Plateau back against the Manihiki Plateau aligns the Manihiki Scarp with the eastern margin of the Rekohu Embayment. Extensional and rotated block faults which formed during the breakup of the combined Manihiki- Hikurangi plateau are interpreted in seismic sections of the Hikurangi Plateau basement. Guyots and ridge- like seamounts which are widely scattered across the Hikurangi Plateau are interpreted to have formed at 99–89 Ma immediately following Hikurangi Plateau jamming of the Gondwana convergent margin at 100 Ma. Volcanism from this period cannot be separately resolved in the seismic reflection data from basement volcanism; hence seamount formation during Manihiki-Hikurangi Plateau emplacement and breakup (125–120 Ma) cannot be ruled out. Seismic reflection data and gravity modeling suggest the 20- Ma-old Hikurangi Plateau choked the Cretaceous Gondwana convergent margin within 5 Ma of entry. Subsequent uplift of the Chatham Rise and slab detachment has led to the deposition of a Mesozoic sedimentary unit that thins from 1 km thickness northward across the plateau. The contrast with the present Hikurangi Plateau subduction beneath North Island, New Zealand, suggests a possible buoyancy cutoff range for LIP subduction consistent with earlier modeling. Components: 16,498 words, 21 figures, 1 table. Keywords: Hikurangi Plateau; Large Igneous Province; Gondwana; Chatham Rise; Manihiki Plateau; subduction. Index Terms: 8178 Tectonophysics: Tectonics and magmatism; 8137 Tectonophysics: Hotspots, large igneous provinces, and flood basalt volcanism; 8104 Tectonophysics: Continental margins: convergent. Received 11 October 2007; Revised 17 April 2008; Accepted 30 April 2008; Published 3 July 2008. Davy, B., K. Hoernle, and R. Werner (2008), Hikurangi Plateau: Crustal structure, rifted formation, and Gondwana subduction history, Geochem. Geophys. Geosyst., 9, Q07004, doi:10.1029/2007GC001855. Copyright 2008 by the American Geophysical Union 1 of 31 Geochemistry 3 davy et al.: hikurangi plateau—crustal structure and history Geophysics 10.1029/2007GC001855 Geosystems G 1. Introduction Java plateaus [Hoernle et al., 2005]. In the Late Cretaceous the Hikurangi plateau has entered, and [2] The Hikurangi Plateau is a Large Igneous been partially subducted beneath, the interpreted Province (LIP) [Mortimer and Parkinson, 1996; Gondwana subduction margin along the north Mahoney and Coffin, 1997; Hoernle et al., 2003], Chatham Rise. The buoyant 20 Ma old plateau one of the many Early Cretaceous LIPs that are choked the subduction system leading to the ces- found in the Pacific [Coffin and Eldholm, 1993] sation of subduction along this section of the (Figure 1). The Hikurangi Plateau (Figure 1) has margin [Bradshaw, 1989; Davy, 1992; Wood and been recently interpreted as part of a much larger Davy, 1994]. (3.6 Â 106 km2), 120 Ma, combined Ontong- Java/Manihiki/Hikurangi Plateau (OJMHP) [Taylor, [4] Early reconnaissance seismic reflection survey- 2006; K. Hoernle et al., The Hikurangi Large ing of the Hikurangi Plateau generally involved Igneous Province: Two major Cretaceous volcanic low-fold seismic reflection surveying with subsea- events, manuscript in preparation, 2008]. The resul- floor penetration of 1–2 s Two-Way Travel time tant superplateau would have formed the largest (TWT) [Wood and Davy,1994].Deepcrustal known oceanic plateau on Earth; however the origin seismic reflection surveying undertaken in 2001 of such a voluminous eruption of magma over an as part of New Zealand’s UNCLOS (United apparently short interval (a few million years) Nations Commission for the Law of the Sea) remains enigmatic [Taylor, 2006; Ingle and Coffin, continental shelf delineation program, combined 2004; Fitton et al., 2004; Tarduno et al., 1991]. with dredge and swath bathymetry data collected by the 2002 SO168 survey by R/V Sonne [Hoernle [3] The Hikurangi Plateau includes numerous large et al., 2003, 2004], has revealed much of the seamounts and other volcanic features, one of the crustal structure detailing the formation, rift, drift longest submarine channels in the world, the and subduction history of the plateau. This paper Hikurangi Channel [Lewis, 1994], thick sediments focuses on the interpretation of these data, and in along the southern, eastern and western margins, particular deep crustal seismic line HKDC1, which and a steep, faulted boundary in the north traverses 1000 km from the ocean crust north of the (Figure 2). Average depth of the plateau is plateau to the crest of the Chatham Rise to the 2,500–4,000 m, similar to the depth range of the south of the plateau (Figure 1). Manihiki Plateau. In contrast the Ontong Java plateau lies at depths of 1500–4000 m. The Hikur- [5] Examination of line HKDC1, as well as sec- angi Plateau is interpreted to have rifted apart from tions of lines less than 300 km further east, enables the OJMHP at 120 Ma and drifted south from the the following: Manihiki Plateau as a result of seafloor spreading [6] 1. Rift structures associated with Manihiki- at the Osbourn Trough [Lonsdale, 1997; Billen and Hikurangi Plateau breakup 120 Ma are recognized. Stock, 2000; Downey et al., 2007] (Figure 1). Basement rocks of the Hikurangi Plateau dredged [7] 2. The fossil Gondwana convergent margin from the base of the Rapuhia Scarp, the northern including the fossil accretionary prism and sub- margin of the plateau, have geochemical composi- ducted Hikurangi Plateau basement is identified tions similar to the Ontong Java Plateau [Mortimer (interpreted from seismic data) beneath the central- and Parkinson, 1996; Hoernle et al., 2005]. Late northern Chatham Rise. Along HKDC1 this base- Cretaceous sediments have been dredged from ment extends 100 km south beneath the Chatham seamounts on the plateau [Strong, 1994] and were Rise from the toe of the accretionary prism to an also drilled near the northeast margin of the Hikur- interpreted leading southern edge of the plateau. angi Plateau at ODP site 1124 (Figures 2 and 3). [8] 3. The widespread volcanism within the pla- Rocks dredged by R/V Sonne survey SO168 teau including an interpreted 0.5–1.5 km thick [Hoernle et al., 2003] from the northern plateau volcaniclastic/limestone/chert layer overlying ba- basement are tholeiitic basaltic to gabbroic samples saltic basement is interpreted. The favored model 94–118 Ma in age (Hoernle et al., manuscript in for plateau volcanism involves guyot formation preparation, 2008). The geochemistry, flat chon- 99–89 Ma, a period which immediately follows drite-normalized REE patterns and enriched mantle the cessation of Mesozoic subduction beneath the (EM)-type isotopic compositions, and the age dis- Chatham Rise. An alternative possibility, that the tribution of these rocks are very similar to that of guyots formed soon after plateau formation and the basement rocks from Manihiki and Ontong- breakup at 120 Ma with later 89–99 Ma volca- 2of31 Geochemistry 3 davy et al.: hikurangi plateau—crustal structure and history Geophysics 10.1029/2007GC001855 Geosystems G Figure 1. Bathymetry of the Hikurangi Plateau–Manihiki Plateau region of the SW Pacific [from Smith and Sandwell, 1997]. Bathymetry contour interval is 500 m. Water depths shallower than 4500 m on the Hikurangi and Manihiki plateaus have been shaded gray. Deep crustal seismic reflection lines collected across the Hikurangi Plateau in 2001 by Geco Resolution are indicated by black and red lines. Thickened red sections on HKDC1 and HKDC3 are shown in Figures 4–10. nism erupting on top of existing peaks, cannot of the New Zealand sector of the Gondwana however be discounted. subduction margin. Using the interpretation of seismic line HKDC1 and others, this paper will [9] Wood and Davy [1994] noted the difference in also focus on the earlier history of the Hikurangi crustal structure in the Hikurangi Plateau across the Plateau formation; the interpreted rifting apart from 176°W longitude (e.g., dashed line in Figure 2). a larger LIP, the transport of the plateau southward East of 176°W crustal and sedimentary structure of and eventual subduction beneath the Gondwana the plateau has a pervasive northeast orientation convergent margin. and appears closely linked to the nature of the interpreted Late Cretaceous Wishbone Ridge line- ation extending northeast from the Chatham Rise 2. Hikurangi Plateau Structure (Figures 1 and 3) [Davy, 2004]. The Wishbone Ridge has been interpreted by Davy [2004] as [10] The crust of the Hikurangi Plateau has been being a crustal boundary involved in the breakup estimated, on the basis of gravity models, to be 3of31 Geochemistry 3 davy et al.: hikurangi plateau—crustal structure and history Geophysics 10.1029/2007GC001855 Geosystems G Figure 2. Bathymetry of the Hikurangi Plateau from Charting Around New Zealand Group (CANZ) [1997]. Bathymetry contour interval is 250 m. Red dashed lines mark postulated segmentation of the Chatham Rise into three (possibly four) sections. Black dashed line marks boundary between southeastern plateau dominated by northeastern volcanic grain and the rest of the Hikurangi Plateau.
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