Research Article| December 01, 1999 Enigmatic extinct spreading center in the West Philippine backarc basin unveiled Kantaro Fujioka; Kantaro Fujioka 1Japan Marine Science and Technology Center, Yokosuka 237-0061, Japan Search for other works by this author on: GSW Google Scholar Kyoko Okino; Kyoko Okino 2Hydrographic Department of Japan, Tsukiji, Tokyo 104-0045, Japan Search for other works by this author on: GSW Google Scholar Toshiya Kanamatsu; Toshiya Kanamatsu 1Japan Marine Science and Technology Center, Yokosuka 237-0061, Japan Search for other works by this author on: GSW Google Scholar Yasuhiko Ohara; Yasuhiko Ohara 2Hydrographic Department of Japan, Tsukiji, Tokyo 104-0045, Japan Search for other works by this author on: GSW Google Scholar Osamu Ishizuka; Osamu Ishizuka 3Geological Survey of Japan, Tsukuba, Ibaraki 305-8567, Japan Search for other works by this author on: GSW Google Scholar Saturu Haraguchi; Saturu Haraguchi 4Ocean Research Institute, University of Tokyo, Nakano, Tokyo 164-8639, Japan Search for other works by this author on: GSW Google Scholar Teruaki Ishii Teruaki Ishii 4Ocean Research Institute, University of Tokyo, Nakano, Tokyo 164-8639, Japan Search for other works by this author on: GSW Google Scholar Geology (1999) 27 (12): 1135–1138. https://doi.org/10.1130/0091-7613(1999)027<1135:EESCIT>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Kantaro Fujioka, Kyoko Okino, Toshiya Kanamatsu, Yasuhiko Ohara, Osamu Ishizuka, Saturu Haraguchi, Teruaki Ishii; Enigmatic extinct spreading center in the West Philippine backarc basin unveiled. Geology 1999;; 27 (12): 1135–1138. doi: https://doi.org/10.1130/0091-7613(1999)027<1135:EESCIT>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Central Basin fault in the center of the West Philippine Basin was first discovered ∼50 yr ago. It is a 1000-km-long ridge oriented northwest to southeast and is cut by north-south–trending fracture zones. Hypotheses about the origin and development of the Central Basin fault have remained unresolved until recently. Submersible observations and SeaBeam surveys show that the Central Basin fault is a segmented spreading ridge having a morphology similar to that of a slow spreading ridge, with a nontransform offset, a nodal deep, and an inside corner high. The distance from the ridge versus the depth of the sea floor, the obliqueness of sets of small trough and ridge structures, and heat-flow values both of the crestal and off-axis areas of the Central Basin fault suggest that the fault is not a simple spreading center, but rather underwent multiple spreading episodes. The texture and chemistry of basalts obtained from the ridge suggest that the lavas were formed in a backarc basin setting. These data confirm that the Central Basin fault is a slow backarc spreading center that has a more complicated evolutionary history than previously realized. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Basalts from the Sumisu caldera volcano range from highlydepleted, wet basalts (low-Zr basalts) to moderately depleted dry basalts (high-Zr basalts). Higher degrees of partial melting in the source mantle are closely related to higher water contents. Our results suggest that within a single volcanic complex, the water content in the mantle source region can be heterogeneous, which results in different degrees of partial melting of this source. An interesting alternative is that the sources are variably depleted before addition of the water and that the extent to which such component is added is a function of the extent of prior depletion. Then the next question is how the upper mantle can be made locally heterogeneous. Thus it is interesting to consider the configuration of such a mantle source region, resulting in heterogeneously depleted residues beneath a single volcanic system such as Sumisu. As a configuration of such a mantle source region, mantle diapir model might be applicable in the Sumisu area.
Abstract. A key component of subduction initiation rock suites is boninite, a high-magnesium andesite that is uniquely predominant in Western Pacific forearc terranes and in select Tethyan ophiolites such as Oman and Troodos. We report the discovery of low-calcium, high-silica boninite in the middle Eocene Zambales ophiolite (Luzon island, Philippines). Olivine-orthopyroxene microphyric high-silica boninite, olivine-clinopyroxene-phyric low-silica boninite and boninitic basalt occur as lapilli fall deposits and pillow lava flows in the upper volcanic unit of the juvenile arc section (Barlo locality, Acoje Block) of Zambales ophiolite. This upper volcanic unit in turn overlies a lower volcanic unit consisting of basaltic andesite, andesite to dacitic lavas and explosive eruptives (subaqueous pahoehoe and lobate sheet flows, agglutinate, and spatter deposits) forming a low-silica boninite series. The overall volcanic stratigraphy of the extrusive sequence at Barlo resembles Holes U1439 and U1442 drilled by IODP Expedition 352 in the Izu-Ogasawara (Bonin) trench slope. The presence of proto-arc basalts in Coto Block (45 Ma), boninite and boninite series volcanics in Barlo, Acoje Block (44 Ma) and simultaneous and post-boninite moderate-Fe arc tholeiites in Sual and Subic, Acoje Block (44–43 Ma) indicate that the observed subduction initiation stratigraphy in the Izu-Ogasawara-Mariana forearc is present in Zambales ophiolite as well. Paleolatitudes derived from tilt-corrected sites in the Acoje Block place the juvenile arc of northern Zambales ophiolite in the western margin of the Philippine Sea Plate. In this scenario, the origin of Philippine Sea Plate boninites (IBM and Zambales) would be in a doubly-vergent subduction initiation setting.
Palau Islands, 7 derajat 30 N, are the only emergent feature on the more than 2500-km¬long Kyushu-Palau Ridge. Small islands are mainly uplifted reef carbonate. Larger islands are volcanic with basalt to dacite and rare boninite. Polymict breccia is abundant: sills, flows, and dykes are common but pillows are rare. Palau Trench samples include all types found on the islands as well as high-Mg basalt. Volcanism began in the late Eocene and ended by early Miocene. All igneous rocks comprise a low-K primitive island arc-tholeiite series. None are mid-ocean ridge basalts. Rare earth elements and high field-strength elements indicate a depleted mantle source. Elevated large ion lithophile elements and light rare earth elements indicate influx of dehydration fluid. Ce/Ce and Eu/Eu ratios show no evidence for recycling of are-derived clastics. Plate reconstructions and paleomagnetic data suggest that the are probably formed on the trace of a transform fault that migrated northward and rotated clockwise up to 90 derajat. Episodes of transtension caused upwelling of hot mantle into depleted mantle and sheared altered rocks of the transform. Episodes of transpression may have initiated subduetion of old seafloor with a thin cover of pelagie sediments deposited far from terrigenous sediment sources.
Abstract Hole U1395B, drilled southeast of Montserrat during Integrated Ocean Drilling Program Expedition 340, provides a long (>1 Ma) and detailed record of eruptive and mass‐wasting events (>130 discrete events). This record can be used to explore the temporal evolution in volcanic activity and landslides at an arc volcano. Analysis of tephra fall and volcaniclastic turbidite deposits in the drill cores reveals three heightened periods of volcanic activity on the island of Montserrat (∼930 to ∼900 ka, ∼810 to ∼760 ka, and ∼190 to ∼120 ka) that coincide with periods of increased volcano instability and mass‐wasting. The youngest of these periods marks the peak in activity at the Soufrière Hills volcano. The largest flank collapse of this volcano (∼130 ka) occurred toward the end of this period, and two younger landslides also occurred during a period of relatively elevated volcanism. These three landslides represent the only large (>0.3 km 3 ) flank collapses of the Soufrière Hills edifice, and their timing also coincides with periods of rapid sea level rise (>5 m/ka). Available age data from other island arc volcanoes suggest a general correlation between the timing of large landslides and periods of rapid sea level rise, but this is not observed for volcanoes in intraplate ocean settings. We thus infer that rapid sea level rise may modulate the timing of collapse at island arc volcanoes, but not in larger ocean‐island settings.
Three submarine Diamante cross-chain volcanoes in the southern Mariana arc mark a magma-healed zone of along-arc (north–south) extension that allows either mafic mantle-derived basalts or felsic magmas from the middle of thickened arc crust to erupt. The largest volcano is East Diamante, with a well-developed (5×10 km) caldera that formed via violent felsic submarine eruptions beginning nearly 0.5 Ma. One or more of these eruptions also formed a giant submarine dune field extending 30 km to the NW of the volcano. Felsic igneous activity continues at least as recently as c. 20 000 years ago, with emplacement of resurgent dacite domes, some hot enough to power the only black smoker hydrothermal system known in the Mariana arc. In contrast, felsic eruptions do not occur on the two volcanoes to the west, implying that the mid-crustal felsic zone does not underlie the thinner crust of the Mariana Trough back-arc basin. Diamante cross-chain lavas define a medium K suite; mafic lava phenocryst assemblages show arc-like associations of anorthite-rich plagioclase with Fe-rich olivine. Magmatic temperatures for a basaltic andesite and three dacites are c. 1100 °C and c. 800 °C, respectively, typical for cool, wet, subduction-related felsic magmas. Felsic magmas formed under low-P crustal conditions. The Diamante cross-chain is the southernmost of at least seven and perhaps eight Mariana arc volcanoes in a c. 115 km long arc segment characterized by felsic eruptions. This is the ‘Anatahan Felsic Province’, which may have formed above a mid-crustal tonalite body that formed by fractionation or was re-melted when heated by c. 1200 °C mafic, mantle-derived magmas. Across- and along-arc variations suggest that felsic eruptions and dome emplacement occurred when midcrustal tonalite was remobilized by intrusions of mafic magma, while north–south extension facilitated the development of conduits to the surface.
