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Origin of Indian Ocean Seamount Province by Shallow Recycling of Continental Lithosphere

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Origin of Indian Ocean Seamount Province by Shallow Recycling of Continental Lithosphere LETTERS PUBLISHED ONLINE: 27 NOVEMBER 2011 | DOI: 10.1038/NGEO1331 Origin of Indian Ocean Seamount Province by shallow recycling of continental lithosphere K. Hoernle1*, F. Hauff1, R. Werner1, P. van den Bogaard1, A. D. Gibbons2, S. Conrad1 and R. D. Müller2 The origin of the Christmas Island Seamount Province in the 5° S Outsider Seamount Sumatra northeast Indian Ocean is enigmatic. The seamounts do not Java form the narrow, linear and continuous trail of volcanoes 53 Investigator Rise Bali that would be expected if they had formed above a mantle Vening-Meinesz 1,2 3 Cocos- plume . Volcanism above a fracture in the lithosphere is also Keeling Volcanic Province 10° S unlikely, because the fractures trend orthogonally with respect Islands 4¬44 Christmas Island 64 70 65 85 105 to the east–west trend of the Christmas Island chain. Here 56 71 94 40 39 we combine Ar= Ar age, Sr, Nd, Hf and high-precision Pb 47 64 81 107 97 112 104 136 Argo isotope analyses of volcanic rocks from the province with plate 90 95 115 Basin tectonic reconstructions. We find that the seamounts are 47– 47 102 115 Volc. 15° S Prov. 136 million years old, decrease in age from east to west and are Cocos-Keeling Eastern Wharton Basin consistently 0–25 million years younger than the underlying Volc. Prov. Volcanic Province oceanic crust, consistent with formation near a mid-ocean 7 cm yr¬1 ridge. The seamounts also exhibit an enriched geochemical 95° E 100° E 105° E 110° E 115° E signal, indicating that recycled continental lithosphere was present in their source. Plate tectonic reconstructions show Figure 1 j Bathymetric map31 of the Christmas Island Seamount Province that the seamount province formed at the position where West (CHRISP) summarizing seafloor morphology and Ar/Ar ages in millions of Burma began separating from Australia and India, forming years. The CHRISP forms a diffuse volcanic belt with an E–W length of a new mid-ocean ridge. We propose that the seamounts ∼1,800 km and a N–S width of ∼600 km and is divided into four formed through shallow recycling of delaminated continental sub-provinces: (1) Argo Basin (136 Myr), (2) Eastern Wharton Basin lithosphere entrained in mantle that was passively upwelling (94–115 Myr), (3) Vening-Meinesz (64–95 Myr; Christmas Island 37–44 beneath the mid-ocean ridge. We conclude that shallow and 4 Myr), and (4) the Cocos/Keeling (47–56 Myr) volcanic provinces. recycling of continental lithosphere at mid-ocean ridges could Also shown is Outsider Seamount (53 Myr). Plate motion vector and rate be an important mechanism for the formation of seamount from UNAVCO model (http://www.unavco.org). provinces in young ocean basins. Volcanic seamounts are one of the most abundant features on Information S1). The ages of the seamounts and the underlying the ocean floor (>20,000 at least 1 km high4), yet the origin of most crust decrease from east to west: from Argo Basin Province seamounts remains elusive. The diffuse Christmas Island Seamount (AP, 136 Myr; underlying crust 154–134 Myr) to Eastern Wharton Province (CHRISP) extends from the Argo Basin to the Wharton Basin Province (EWP, 115–94 Myr; crust ∼120–105 Myr from SE Basin, west of the Investigator Rise, covering ∼1,000,000 km2 to NW) to Vening-Meinesz Province (VMP, 95–64 Myr; crust (Fig. 1). In addition to Christmas Island and the Cocos/Keeling ∼100–78 Myr from SE to NW) to Cocos–Keeling Province (CKP, Islands, it consists of ∼50 large, up to 4,500 m high seamounts, 56–47 Myr; crust 67–61 Myr from S to N; refs 5,6; Fig. 1). A plot of and abundant smaller volcanic structures. During the RV Sonne longitude versus age forms a good linear correlation (r 2 D0:87). The SO199 CHRISP Expedition, 54 seamounts were partially mapped age difference between a seamount sample and the underlying crust with the SIMRAD EM 120 multi-beam echo-sounding system and is 0–25 Myr, indicating that the seamounts formed on or near the 38 were sampled by dredging. The recovered rocks indicate that West Burma–Australian/Indian spreading ridge. Christmas Island all structures are volcanic in origin. Compositions range from and its submarine flanks record two younger, intraplate phases of tholeiitic to basanitic to trachytic, with alkali basalts being the main volcanism: (1) the Eocene shield phase (44–37 Myr) and (2) the parental lava type. The abundant large guyots indicate that this was Pliocene late phase (4.5–4.3 Myr). a former province of ocean island volcanoes, which were eroded The isotopic compositions of the CHRISP display a large range to sea level and subsequently subsided (1,200–3,000 m). The goal (Supplementary Table S2; Fig. 2) and extend to more enriched of this study was to constrain the origin of the CHRISP and to compositions than endmember enriched mantle one (EM1)-type determine if its source(s) could have affected the chemistry of the hotspot volcanism, such as Pitcairn Island and Walvis Ridge, but Indian upper mantle. overlap with the Afanasy–Nikitin Rise and Seamount, volcanic Step-heating plateau ages on plagioclase, hornblende, K- structures on the sea floor south of India7,8. On the uranogenic feldspar, glass and matrix separates were generated from 32 Pb isotope diagram, the CHRISP samples overlap the Indian mid- seamount and 10 Christmas Island samples (Supplementary ocean-ridge basalt (MORB) field but extend to higher 207Pb=204Pb 1IfM-GEOMAR Leibniz Institute of Marine Sciences, Wischhofstrasse 1-3, Kiel 24148, Germany, 2EarthByte Group, School of Geosciences, University of Sydney, NSW 2006, Australia. *e-mail: [email protected]. NATURE GEOSCIENCE j ADVANCE ONLINE PUBLICATION j www.nature.com/naturegeoscience 1 © 2011 Macmillan Publishers Limited. All rights reserved. LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO1331 207 204 143 144 a W-CHRISP E-CHRISP Christ. Is.: LVS Pb= Pb (14.8–15.4) and Nd= Nd (0.5114-7; ref. 11). Mixing 15.75 VMP EWP Christ. Is.: UVS of Pacific/N. Atlantic MORB and metasomatized SCLM with NW Australia CKP AP Outsider Smt. 15.70 lamproites compositions similar to lamproites and the Millindinna Complex S-Atlantic and/or continental crust can explain the full range of compositions 15.65 Afanasy-Nikitin found in the Indian Ocean, including CHRISP, Afanasy–Nikitin 15.60 Rise Pb and Indian MORB (Fig. 2). SWIR 204 Propagating fault or mantle plume models are generally invoked 15.55 39°¬41°E N-Atlantic Pb/ to explain the origin of age-progressive island/seamount volcanism. 15.50 207 W As all major faults and fracture zones (for example, Investigator P Pacific 15.45 Rise) in the NE Indian Ocean have a N–S rather than E–W Smt. Indian Afanasy-Nikitin 15.40 strike (Fig. 1), tectonic structures on the sea floor cannot explain na C. the E–W elongation and age progression of the CHRISP. The Smokey Butte L. Millindin 16.5 17.0 17.5 18.0 18.5 19.0 19.5 plume hypotheses also cannot adequately explain the origin of the 206Pb/204Pb CHRISP, because (1) there are no known hotspots that could have b formed this volcanic chain, (2) the CHRISP is much wider (up to Pacific 0.5132 N-Atlantic 600 km) and discontinous than well-defined, continuous hotspot Indian 0.5130 tracks, for example, the Hawaiian and Louisville island/seamount chains (<200 km wide), (3) >100 Myr of volcanism occurred 0.5128 P ° E SWIR °¬41 within 150 km of Christmas Island, (4) the beginning of the Nd 0.5126 39 S-Atlantic CHRISP, unlike many hotspots (for example, Tristan/Gough, 144 W 0.5124 Réunion and Galápagos), is not associated with a large-scale Nd/ 0.5122 Afanasy- Afanasy-Nikitin Rise 143 flood basalt event, and (5) the volcanism in the CHRISP ends Nikitin iteSmt. 0.5120 ∼ 12 NW Australia lamproites at 50 Myr. Plate tectonic reconstructions made using GPlates 0.5118 Smokey Butte lampro (Supplementary Information S3) provide further evidence against a 0.5116 Millindinna Complex plume origin for the CHRISP (Fig. 3). Although a stationary plume 0.5114 16.5 17.0 17.5 18.0 18.5 19.0 19.5 located beneath the AP at 136 Myr could also have formed the EWP (115–94 Myr), it could not have generated younger volcanism c 206Pb/204Pb in the EWP (93–70 Myr), VMP and Christmas Island (95–4 Myr) E Nd or CKP (56–47 Myr). Models involving a migrating plume also ¬30 ¬25 ¬20 ¬15 ¬10 ¬5.0 0 5.0 10 40 cannot adequately explain the morphology, width, elongation and 30 age progression of the CHRISP. 0.2835 N-Atlantic Indian 20 The plate tectonic reconstructions, however, place extra con- Walvis straints on the origin of the CHRISP. They show that the CHRISP 0.2830 10 Hf Pacific Pitcairn E Hf formed at the same location where West Burma separated from 177 0 S-Atlantic Australia and Greater India (Fig. 3). Therefore, SCLM and/or lower Hf/ 0.2825 ¬10 176 crust simply needed to be removed from the base of the separating Mantle Array ¬20 blocks and recycled to form the CHRISP (Fig. 4). Outcrops of the 0.2820 ¬30 Indian NW Australian lamproites and Millindinna Complex are within lamproites ¬40 0.2815 500 km of the rifted margin (Fig. 3a). Combined seismic tomogra- ¬50 0.5110 0.5115 0.5120 0.5125 0.5130 phy, uplift patterns, temporal variations in age and geochemistry of 143Nd/144Nd volcanism and numerical modelling provide compelling evidence that continental lithosphere and lower crust are being delaminated Figure 2 j The CHRISP volcanism displays a large range in isotopic at present-day continental rifts, such as the margins of the Basin composition.
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