Depleted mantle wedge and sediment fi ngerprint in unusual basalts from the Manihiki Plateau, central Pacifi c Ocean Stephanie Ingle* Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan John J. Mahoney School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822, USA Hiroshi Sato School of Business Administration, Senshu University, Kanagawa 214-8580, Japan Millard F. Coffi n Ocean Research Institute, University of Tokyo, Tokyo 164-8639, Japan Jun-Ichi Kimura Department of Geoscience, Shimane University, Matsue 690-8504, Japan Naoto Hirano Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan Masao Nakanishi Graduate School of Science and Technology, Chiba University, Chiba 263-8522, Japan 200°W 180° 160° ABSTRACT 50° 170°W 165° 160° 0 0 0 5 - 0 0 0 5 -5000 - 00 0 50 0 - 0 -5 - 5 00 0 -50 0 0 -5 0 Numerous large igneous provinces formed in the Pacifi c Ocean ABManihiki Plateau00 - 00 50 -50 00 00 -4 -50 0 0 0 -50 -5 00 0 0 0 -5 000 0 0 0 5 00 - -50 -5000 - 5 -5 0 -50 0 0 -5 00 0 0 0 00 0 -5 -5 0 00 0 0 0 -500 0 Hess - 5 0 0 0 -5 0 0 -3 -5 0 0 0 0 00 0 0 -5 40°N 0 -4 0 0 0 - -5 0 4 000 00 0 0 0 - -4 -3 0 5 0 0 0 0 0 0 -5000 -5000 0 - 0 5000 -30 0 during Early Cretaceous time, but their origins and relations are -500 0 0 0 - 0 5 4 0 - 0 -50 0 0 0 00 -4000 -5 -3 0 00 -5000 - 000 4 -5 0 0 0 00 50 - -5000 000 0 -4 00 -3 -4 0 0 0 000 -5000 -5 0 0 0 -3 -50 00 00 0 0 0 -5 0 4 - 00 - -50 5000 - 0 3 0 0 0 0 5 0 - - 40 -2 00 0 00 0 0 0 0 0 0 5 0 00 0 - 0 30 0 -4 -3 - -400 -2 00 0 0 0 poorly understood. We present new geochronological and geochemi- 0 -4000 00 5 -40 - 5°S 0 0 -30 -300 0 0 0 -5 - 40 0 30°N 4000 - 0 0 0 0 000 0 -4 5 -4000 - -5000 -5 -5 00 000 0 000 00 -5 40 - 00 -30 0 0 0 -5 0 0 0 5 Shatsky - -4000 -500 0 -30 - 3 00 0 0 00 0 -4 0 -4000 -3 0 0 0 -30 0 0 -500 00 0 0 -5 0 0 0 0 0 5 40 - -5 - 000 -30 0 0 0 0 - -500 0 5000 00 0 0 0 4 0 5 - 50 -5000 -500-0 - 00 -4000 0 5 cal data on rocks from the Manihiki Plateau and compare these results - - 50 00 -4000 -4 0 0 0 00 0 -5 -5 000 0 0 000 0 -30 -5 -3 0 000 0 -5 -5 -5 0 000 0 0 00 - 0 50 5 00 - 0 0 -500 0 0 6 - -5 0 0 20°N 0 00 0 - 5000 -5 4 - 0 0 0 D4 -50 00 -3 0 0 - 0 -4 4 000 0 -5 0 - 0 5 00 0 0 0 00 0 -4 -5 0 0 0 0 0 0 0 4 - 00 0 40 0 - 0 0 - 00 -3 6000 -6 -2 0 0 00 0 0 -4 0 0 00 0 0 -5 0 -5 00 4 0 0 to those for other Cretaceous Pacifi c plateaus. A dredged Manihiki - 0 3 - 00 -40 -400 0 0 0 00 0 -5 0 -5000 3 - -40 - 50 00 -5000 00 0 -4 -300 -4000 000 0 0 0 0 4 - 00 -3 0 00 -4 -4 Magellan 00 0 000 -4 00 0 0 0 0 0 0 4 -5 - 50 -5000 - -400 0 00 00 -20 -50 0 10°N 0 0 40 39 3 - -4 00 0 -3 00 00 -40 0 00 σ 40 - 0 -4 00 000 -4 -4 0 0 0 - 2 0 0 basalt gives an Ar- Ar age of 117.9 ± 3.5 Ma (2 ), essentially con- 0 - 3 0 0 0 78D -4 00 0 0 00 -4 0 0 0 0 0 0 0 -4 0 0 4 0 - 0 -5 -3000 -50 00 -30 0 0 0 -4 00 -40 00 -30 D3 0 00 -4000 -4 -30 00 0° -5 0 0 0 0 0 0 -3 0 -4 00 00 0 4 40 0 - - 0 -3000 0 00 -4 temporaneous with the Ontong Java Plateau ~2500 km to the west, -4 000 - 5 0 0 0 0 0 0 -4000 0 0 60 - 4 -4000 - -2 00 0 0 -4 0 0 0 0 -4 0 -3 0 0 0 00 00 0 0 5 00 0 - 0 4 3 0 - - 0 40 0 - 20 - 00 -40 -4000 0 Ontong 0 D2 0 -5 -3000 -4 0 0 0 0 0 0 2 - - 30 MWD 00 0 0 -40 0 00 -3 - 30 00 -5 000 0 -400 -5000 10°S - 0 30 0 00 0 0 4 0 - 0 Java 10°S -1 and the possibly related Hikurangi Plateau ~3000 km to the south. 0 00 00 -40 -4 -4 0 0 0 -2000 00 -30 - 0 5 0 00 0 4 - -5 0 0 00 00 0 -5 00 - 0 4 -5 0 0 0 000 -4 -4 0 00 -5000 0 0 - 0 -4000 4 -5 0 0 0 -1000 - 5000 - 20 00 00 -30 -50 00 - 0 30 00 00 0 -50 -5 0 0 0 0 0 0 0 -2 -4 00 -5000 50 -3 - 0 00 00 0 -5 -4 0 0 0 -4 0 0 0 - 0 0 50 0 0 Drilled Manihiki lavas are tholeiitic with incompatible trace element 4 0 - 0 00 -5 0 00 - 50 -2 0 0 - 0 3 0 0 0 5 00 0 - 5 0 0 - - 0 3 0 - 0 30 0 5 0 0 - 20°S 0 0 -4000 -5 0 Danger Islands00 317 -5 Manihiki 000 -5 00 0 -4 0 00 abundances similar to those of Ontong Java basalts. These lavas may -5000 -50 00 -4 00 0 0 0 0 5 Troughs - - 4 0 0 -50 0 00 00 30°S -50 - 5000 0 0 0 5 - 0 0 -4 00 0 0 10 4 0 - - 0 00 20 0 - 0 0 5 -3000 - - 30 00 - 50 result from high degrees of partial melting during the main eruptive 00 0 -500 0 - 00 50 -5 -4 0 0 0 0 0 00 0 5 - 00 00 0 -50 -4 -5 00 -5000 0 0 0 0 0 500 -5 - 0 00 -5 0 0 -5 0 -50 000 0 0 5 - 00 -50 -2000 0 300 0 - 0 0 4 - 0 0 0 0 4 Hikurangi 00 0 - -1 0 0 -3000 -5 - 5 40°S 0 0 0 - 5 0 0 0 0 0 0 phase of plateau formation. There are two categories of dredged lavas 0 0 2 - 0 0 4 0 - 0 -5 - 30 00 0 0 0 0 0 -400 0 5 - 0 0 0 0 5 - 400 0 - -50 0 0 5 - -50 00 -5 0 0 Predicted Bathymetry (km) 0 0 0 0 0 0 5 0 00 - 0 -5 - 0 -4 5 0 0 0 0 0 5 - 00 -50 00 -50 0 0 - 5 -50 0 -500 0 0 0 0 0 0 5 0 - 15°S 00 -5 0 0 0 5 - - from the Danger Islands Troughs, which bisect the plateau. The fi rst is 5000 - 5000 -5 0 0 0 -5 0 0 0 -5 - 00 50 0 50° -800 -7 -6 -5 -4 -3 -2 -1 0 alkalic lavas having strong enrichments in light rare earth and large- 190°W 170° 150° 170°W 165° 160° ion lithophile elements; these lavas may represent late-stage activity, as one sample yields an 40Ar-39Ar age of 99.5 ± 0.7 Ma. The second Figure 1. A: Locations of large western Pacifi c plateaus and rises. B: Bathymetric map with locations of Site 317 and KH03–01 Leg 5 category consists of tholeiitic basalts with U-shaped incompatible ele- (D2–D4), SOTW (78D), and seamount (MWD) dredges. Strikes of ment patterns and unusually low abundances of several elements; Danger Islands Troughs are indicated. these basalts record a mantle component not previously observed in Manihiki, Ontong Java, or Hikurangi lavas. Their trace element characteristics may result from extensive melting of depleted mantle wedge material mixed with small amounts of volcaniclastic sediment. 1974). It is interpreted as having formed during active rifting (Winterer We are unaware of comparable basalts elsewhere. et al., 1974), from arrival of a large mantle plume head (Mahoney and Spencer, 1991), or a combination of the two (Larson, 1997). Biostratig- Keywords: large igneous provinces, Early Cretaceous, Manihiki Plateau, raphy suggests that its minimum age is late Aptian (Bukry, 1976). Igneous Pacifi c Ocean, geochemistry, geochronology. rocks have been sampled from Deep Sea Drilling Project Site 317 (24.5 m of cored basalt; Jackson et al., 1976), a few dredge locations in the Danger INTRODUCTION Island Troughs (herein referred to as “Troughs”) (Clague, 1976), and two Early Cretaceous time was marked by the formation of numerous seamounts on the eastern fl ank of the plateau (Beiersdorf et al., 1995; large igneous provinces (LIPs) in amounts vastly exceeding their forma- Fig.