Backarc Basin

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Yasuhiko Ohara - One of the best experts on this subject based on the ideXlab platform.

  • Termination of Backarc spreading: Zircon dating of a giant oceanic core complex
    Geology, 2010
    Co-Authors: Kenichiro Tani, Daniel J. Dunkley, Yasuhiko Ohara
    Abstract:

    The Godzilla megamullion is the largest oceanic core complex (OCC) currently known, and is adjacent to the spreading center of the Parece Vela Basin (PVB), an extinct Backarc Basin in the Philippine Sea. The duration and termination of tectonomagmatic processes during OCC formation are poorly constrained, due to the weak geomagnetic anomalies in the region. Zircon U-Pb dating of gabbroic and leucocratic rocks from the Godzilla megamullion reveals that fault-induced spreading over the ∼125 km length of the OCC lasted for ∼4 m.y., with continuous magmatic accretion at the spreading axis. The latest magmatism constrains the cessation of PVB spreading to ca. 7.9 Ma or later, significantly younger than a previous estimate of ca. 12 Ma. The new ages show that Backarc Basin formation migrated to the present-day Mariana Trough soon after the cessation of spreading in the PVB.

  • Peridotites and gabbros from the Parece Vela Backarc Basin: Unique tectonic window in an extinct Backarc spreading ridge
    Geochemistry Geophysics Geosystems, 2003
    Co-Authors: Yasuhiko Ohara, Kantaro Fujioka, Teruaki Ishii, Hisayoshi Yurimoto
    Abstract:

    [1] Peridotite samples from a Backarc Basin setting will help better understand global mid-oceanic ridge processes. Here we report detailed petrological data of serpentinized peridotite and gabbro from the extinct Parece Vela Basin in the Philippine Sea. Despite its relatively fast spreading rate (8.8–7.0 cm/y full-rate), the Parece Vela Basin spreading ridge (the Parece Vela Rift) has the distinct morpho-tectonic characteristics that indicate a small degree of mantle melting, including the presence of a huge mullion structure (the Godzilla Mullion). Peridotites in the Parece Vela Rift are exposed on the Godzilla Mullion as well as at a segment midpoint. The most notable characteristic of Parece Vela Rift peridotites is small-scale juxtaposition (i.e., a single-dredge-haul scale) of fertile peridotite and depleted peridotite (dunite and plagioclase-bearing peridotite). We interpret that the fertile peridotite (F-type) is the residue of a small degree of mantle melting (∼4% near-fractional melting of a MORB-type mantle), whereas dunite (D-type) and plagioclase-bearing peridotite (P-type) are products of melt-mantle interaction. The associated evolved gabbros may represent the shallow level fractionated melt intruded into P-type. The distinct morpho-tectonic characteristics, peridotite exposure at a segment midpoint, and the presence of fertile peridotite may result from an extreme transform fault effect caused by the ridge-transform geometry of short first-order segments sandwiched by closely spaced fracture zones (“transform sandwich effect”).

  • Giant Megamullion in the Parece Vela Backarc Basin
    Marine Geophysical Researches, 2001
    Co-Authors: Yasuhiko Ohara, Tsuyoshi Yoshida, Yukihiro Kato, Shigeru Kasuga
    Abstract:

    We present results of high-resolution bathymetric studies of the extinct intermediate-spreading Parece Vela Basin in the northwestern Pacific, where we have identified an extremely large mullion structure, here termed a giant megamullion. We find that the giant megamullion is nearly an order of magnitude larger than the similar structures in the slow-spreading Mid-Atlantic Ridge (`megamullions'). The giant megamullion has slightly elevated mantle Bouguer anomaly, and yields serpentinized peridotites and gabbros, suggesting that they are exposing oceanic crust and upper mantle. An off-axis rugged `chaotic terrain' was also identified in the Parece Vela Basin. The terrain consists of isolated and elevated blocks capped by corrugated axis-normal lineations, and associated deeps. We thus interpret it as analogues to the Mid-Atlantic Ridge megamullions. We propose that amagmatic tectonics producing the giant megamullion and the chaotic terrain occupied a significant part in crustal construction in the Parece Vela Basin evolution.

  • Enigmatic extinct spreading center in the West Philippine Backarc Basin unveiled
    Geology, 1999
    Co-Authors: Kantaro Fujioka, Kyoko Okino, Toshiya Kanamatsu, Yasuhiko Ohara, Osamu Ishizuka, Saturu Haraguchi, Teruaki Ishii
    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.

Graham W. Gibson - One of the best experts on this subject based on the ideXlab platform.

  • Morphology and history of the Kermadec trench–arc–Backarc Basin–remnant arc system at 30 to 32°S: geophysical profile, microfossil and K–Ar data
    Marine Geology, 1999
    Co-Authors: Peter F. Ballance, Albert G. Ablaev, Igor K Pushchin, Sergei P. Pletnev, Maria G Birylina, Tetsumaru Itaya, Harry A. Follas, Graham W. Gibson
    Abstract:

    Abstract Knowledge of the time span of arc activity, essential for correct tectonic reconstructions, has been lacking for the Kermadec arc system, but is supplied in this paper through study of microfossils contained in dredge samples, and K–Ar ages on dredged basalt clasts. The Kermadec system at south latitudes 30 to 32° in the southwest Pacific comprises from west to east the Colville Ridge (remnant arc), Havre Trough (Backarc Basin), Kermadec Ridge (active arc) and Kermadec Trench (site of west-dipping subduction of Pacific plate lithosphere beneath the Australian plate). Data are presented from two traverses (dredge, magnetic, single-channel seismic) across the whole system. An important transverse tectonic boundary, the 32°S Boundary, lies between the two traverse lines and separates distinct northern (32–25°S) and southern (32–36°S) sectors. The northern sector is shallower and well sedimented with broad ridges and a diffuse Backarc Basin. The southern sector is deeper with narrow ridges and steep escarpments facing inwards to a little-sedimented, rifted Backarc Basin. The Kermadec Ridge slopes smoothly trenchward to a mid-slope terrace (forearc Basin) with minor sediment fill at 5–6 km water depth. A steeper (10–24°) and more rugged lower trench slope is mantled with New Zealand-sourced rhyolitic vitric mud diamictons containing locally derived mafic volcanic clasts; one clast is of late Miocene age (K–Ar age 7.84 Ma). The arc (Kermadec Ridge) is capped by active volcanoes; very young K–Ar ages (

  • morphology and history of the kermadec trench arc Backarc Basin remnant arc system at 30 to 32 s geophysical profile microfossil and k ar data
    Marine Geology, 1999
    Co-Authors: Peter F. Ballance, Albert G. Ablaev, Igor K Pushchin, Sergei P. Pletnev, Maria G Birylina, Tetsumaru Itaya, Harry A. Follas, Graham W. Gibson
    Abstract:

    Abstract Knowledge of the time span of arc activity, essential for correct tectonic reconstructions, has been lacking for the Kermadec arc system, but is supplied in this paper through study of microfossils contained in dredge samples, and K–Ar ages on dredged basalt clasts. The Kermadec system at south latitudes 30 to 32° in the southwest Pacific comprises from west to east the Colville Ridge (remnant arc), Havre Trough (Backarc Basin), Kermadec Ridge (active arc) and Kermadec Trench (site of west-dipping subduction of Pacific plate lithosphere beneath the Australian plate). Data are presented from two traverses (dredge, magnetic, single-channel seismic) across the whole system. An important transverse tectonic boundary, the 32°S Boundary, lies between the two traverse lines and separates distinct northern (32–25°S) and southern (32–36°S) sectors. The northern sector is shallower and well sedimented with broad ridges and a diffuse Backarc Basin. The southern sector is deeper with narrow ridges and steep escarpments facing inwards to a little-sedimented, rifted Backarc Basin. The Kermadec Ridge slopes smoothly trenchward to a mid-slope terrace (forearc Basin) with minor sediment fill at 5–6 km water depth. A steeper (10–24°) and more rugged lower trench slope is mantled with New Zealand-sourced rhyolitic vitric mud diamictons containing locally derived mafic volcanic clasts; one clast is of late Miocene age (K–Ar age 7.84 Ma). The arc (Kermadec Ridge) is capped by active volcanoes; very young K–Ar ages (

Robert A. Creaser - One of the best experts on this subject based on the ideXlab platform.

  • Lithosphere-asthenosphere mixing in a transform-dominated late Paleozoic Backarc Basin Implications for northern Cordilleran crustal growth and assembly
    Geosphere, 2012
    Co-Authors: Stephen J. Piercey, Donald C. Murphy, Robert A. Creaser
    Abstract:

    The Slide Mountain terrane is part of a North American Cordillera–long Backarc Basinal assemblage that developed between the ensialic arc terranes (Yukon-Tanana and affiliated pericratonic terranes) and the North American craton in the middle to late Paleozoic. The Slide Mountain Basin started to open in the Late Devonian, and spreading continued through the late Paleozoic in an oblique (transform-dominated) manner such that the pericratonic terranes were translated into southerly latitudes. The Basin closed, also in an oblique manner, by the Early Triassic, resulting in the reaccretion of the Yukon-Tanana terrane to the northwestern Laurentian margin. Both the opening and closing likely involved hundreds to possibly thousands of kilometers of intra-ocean and/or intra-arc strike-slip displacement, sinistral during the ocean9s Late Devonian to mid-Permian opening and dextral during its Late Permian closing. In southeastern Yukon, Canada, the Early Permian Slide Mountain terrane is dominated by mafic and ultramafic volcanic and plutonic rocks of the Campbell Range Formation. These rocks are narrowly distributed, for over 300 km, on either side of the Jules Creek–Vangorda fault, a fault that separates Slide Mountain terrane from Yukon-Tanana terrane. The Campbell Range basaltic volcanic and high-level intrusive rocks have geochemical and isotopic signatures that vary systematically across the Jules Creek–Vangorda fault: ocean-island basalt (OIB) and enriched mid-ocean ridge basalt (E-MORB) suites with lower eNd t occur exclusively south of the fault, whereas north of the fault they have normal mid-ocean ridge basalt (N-MORB) and Backarc Basin basalt (BABB) signatures with higher eNd t values. The eNd t values are inversely correlated with Nb/Th pm and Nb/La pm , suggesting that the lower eNd t values present in the E-MORB and OIB are mantle source features of these basalts and not due to continental crustal contamination. Isotopic and multi-element mixing calculations illustrate that the OIB-like basalts were derived primarily from enriched continental lithospheric mantle, whereas the N-MORB and BABB suites were sourced primarily from the upwelling Backarc asthenospheric mantle; E-MORBs represent mixtures of depleted asthenospheric and enriched lithospheric mantle. The geochemical and isotopic variations in the Campbell Range Formation across the Jules Creek–Vangorda fault is attributed to formation in different parts of an extending continental-Backarc Basin and then their subsequent juxtaposition by continued displacement along the fault. Despite the juvenile isotopic signatures present in the Slide Mountain terrane, they occur as thin klippe atop rocks of recycled continental crustal affinity, suggesting that they were likely only minor contributors to Cordilleran crustal growth.

  • Mid-Paleozoic initiation of the northern Cordilleran marginal Backarc Basin: Geologic, geochemical, and neodymium isotope evidence from the oldest mafic magmatic rocks in the Yukon-Tanana terrane, Finlayson Lake district, southeast Yukon, Canada
    Geological Society of America Bulletin, 2004
    Co-Authors: Stephen J. Piercey, Donald C. Murphy, James K. Mortensen, Robert A. Creaser
    Abstract:

    The Fire Lake formation of the Yukon-Tanana terrane in the Finlayson Lake region, Yukon, Canada, consists primarily of Late Devonian (ca. 365–360 Ma) mafic metavolcanic rocks and smaller volumes of mafic and ultramafic subvolcanic metamorphosed intrusions. In this paper, field, geochemical, and Nd isotope attributes of these rocks are presented in an attempt to understand their tectonic setting, the magmatic processes involved in their formation, and their roles in Cordil-leran crustal growth. The mafic rocks of the Fire Lake formation exhibit a wide diversity of geochemical signatures and are classified into seven chemically defined suites: (1) back-arc-Basin basalt, (2) enriched mid-oceanic-ridge basalt (E-MORB), (3) oceanic-island basalt (OIB), (4) Th-rich OIB, (5) boninite, (6) island-arc tholeiite, and (7) light rare earth element (LREE)–enriched island-arc tholeiite. The diversity of geochemical signatures is interpreted to represent variable mixtures of asthenospheric (MORB-type) mantle, subarc mantle wedge, and lithospheric (OIB-type) mantle with or without elemental contributions from the subducted slab and/or continental crust. These suites of rocks are also associated with fine-grained Basinal sedimentary facies, variations in metavolcanic and metasedimentary unit thickness, extensional synvolcanic faults, and apparent extensional-fault–controlled emplacement of mafic intrusive rocks and hydrothermal volcanic-hosted massive sulfide mineralization. The suites also exhibit a broad spatial distribution; those with “arc” signatures (Nb/Thmn < 1; mn—normalized to primitive mantle values) are located primarily in the western parts of the formation, and suites with “nonarc” signatures (Nb/Thmn ≥ 1) are located primarily within the eastern parts of the formation. Collectively, these geologic and geochemical attributes are interpreted to stem from the transition from arc magmatism to the initiation of an extensional Backarc Basinal environment associated with an east-dipping subduction zone. The initiation of Backarc-Basin magmatism recorded in the Fire Lake formation was part of a much larger Late Devonian Backarc Basinal system forming along the western edge of the margin of North America. The Fire Lake formation is interpreted to represent (1) the commencement of Yukon-Tanana arc rifting and separation from the North American cratonic margin, and (2) the initiation of a marginal (Backarc) Basin (now the Slide Mountain terrane) inboard of the Yukon-Tanana arc system. This tectonic evolution likely occurred either as a result of slab rollback toward the west within the convergent margin responsible for Yukon-Tanana arc activity or as a result of the propagation of the Slide Mountain Backarc-Basin spreading ridges into the Yukon-Tanana arc system. This Yukon-Tanana arc rifting episode was also broadly coincident with rifting and hydrothermal activity within rocks of the North American craton. The geochemical and isotopic signatures of magmatic rocks in the Fire Lake formation have some features similar to intraoceanic arc rocks (e.g., boninites, island-arc tholei-ites), and many have juvenile Nd isotope signatures (i.e., ϵNd( t ) > 0; most have ϵ Nd( t ) > +5), suggesting that the pericratonic terranes of the northern Cordillera have a significant juvenile component. If this is the case throughout the Yukon-Tanana terrane, then the pericratonic terranes may have contributed much more juvenile material to Cordil-leran crustal growth in the Phanerozoic than has previously been considered.

Peter F. Ballance - One of the best experts on this subject based on the ideXlab platform.

  • Morphology and history of the Kermadec trench–arc–Backarc Basin–remnant arc system at 30 to 32°S: geophysical profile, microfossil and K–Ar data
    Marine Geology, 1999
    Co-Authors: Peter F. Ballance, Albert G. Ablaev, Igor K Pushchin, Sergei P. Pletnev, Maria G Birylina, Tetsumaru Itaya, Harry A. Follas, Graham W. Gibson
    Abstract:

    Abstract Knowledge of the time span of arc activity, essential for correct tectonic reconstructions, has been lacking for the Kermadec arc system, but is supplied in this paper through study of microfossils contained in dredge samples, and K–Ar ages on dredged basalt clasts. The Kermadec system at south latitudes 30 to 32° in the southwest Pacific comprises from west to east the Colville Ridge (remnant arc), Havre Trough (Backarc Basin), Kermadec Ridge (active arc) and Kermadec Trench (site of west-dipping subduction of Pacific plate lithosphere beneath the Australian plate). Data are presented from two traverses (dredge, magnetic, single-channel seismic) across the whole system. An important transverse tectonic boundary, the 32°S Boundary, lies between the two traverse lines and separates distinct northern (32–25°S) and southern (32–36°S) sectors. The northern sector is shallower and well sedimented with broad ridges and a diffuse Backarc Basin. The southern sector is deeper with narrow ridges and steep escarpments facing inwards to a little-sedimented, rifted Backarc Basin. The Kermadec Ridge slopes smoothly trenchward to a mid-slope terrace (forearc Basin) with minor sediment fill at 5–6 km water depth. A steeper (10–24°) and more rugged lower trench slope is mantled with New Zealand-sourced rhyolitic vitric mud diamictons containing locally derived mafic volcanic clasts; one clast is of late Miocene age (K–Ar age 7.84 Ma). The arc (Kermadec Ridge) is capped by active volcanoes; very young K–Ar ages (

  • morphology and history of the kermadec trench arc Backarc Basin remnant arc system at 30 to 32 s geophysical profile microfossil and k ar data
    Marine Geology, 1999
    Co-Authors: Peter F. Ballance, Albert G. Ablaev, Igor K Pushchin, Sergei P. Pletnev, Maria G Birylina, Tetsumaru Itaya, Harry A. Follas, Graham W. Gibson
    Abstract:

    Abstract Knowledge of the time span of arc activity, essential for correct tectonic reconstructions, has been lacking for the Kermadec arc system, but is supplied in this paper through study of microfossils contained in dredge samples, and K–Ar ages on dredged basalt clasts. The Kermadec system at south latitudes 30 to 32° in the southwest Pacific comprises from west to east the Colville Ridge (remnant arc), Havre Trough (Backarc Basin), Kermadec Ridge (active arc) and Kermadec Trench (site of west-dipping subduction of Pacific plate lithosphere beneath the Australian plate). Data are presented from two traverses (dredge, magnetic, single-channel seismic) across the whole system. An important transverse tectonic boundary, the 32°S Boundary, lies between the two traverse lines and separates distinct northern (32–25°S) and southern (32–36°S) sectors. The northern sector is shallower and well sedimented with broad ridges and a diffuse Backarc Basin. The southern sector is deeper with narrow ridges and steep escarpments facing inwards to a little-sedimented, rifted Backarc Basin. The Kermadec Ridge slopes smoothly trenchward to a mid-slope terrace (forearc Basin) with minor sediment fill at 5–6 km water depth. A steeper (10–24°) and more rugged lower trench slope is mantled with New Zealand-sourced rhyolitic vitric mud diamictons containing locally derived mafic volcanic clasts; one clast is of late Miocene age (K–Ar age 7.84 Ma). The arc (Kermadec Ridge) is capped by active volcanoes; very young K–Ar ages (

Harmon Craig - One of the best experts on this subject based on the ideXlab platform.

  • high 3he 4he ratios in the manus Backarc Basin implications for mantle mixing and the origin of plumes in the western pacific ocean
    Geology, 1998
    Co-Authors: Colin G. Macpherson, David R. Hilton, John M. Sinton, R. J. Poreda, Harmon Craig
    Abstract:

    Helium isotope ratios in oceanic glasses provide a high-integrity tracer of contributions from mantle plumes. Despite a diverse array of petrogenetic affinities, glasses from the central part of the Manus Basin—a Backarc Basin in the western Pacific—have typical plume (or hotspot) 3 He/ 4 He ratios that cluster around 12.2 R A (±1.0 R A n =18, where R A = 3 He/ 4 He of air), a value significantly higher than the range found in most mid-ocean-ridge basalts (MORB) ([8 ± 1] A ). Lavas in other parts of the Basin have MORB-like or lower 3 He/ 4 He values. A wide range of He concentrations characterizes the Manus Basin glasses: This is considered to reflect the high water content of some lavas, which promotes He loss through volatile degassing. For the most part, it is the degassed lavas that do not show the plume He isotope signature. Results of the present study, together with 3 He/ 4 He data for lavas and gases from islands to the south and east of the Bismark Sea, indicate that the focus of mantle plume upwelling is either the center of the Manus Basin or possibly the region to the northwest beneath the volcanic islands of the St. Andrew Strait. This region of plume or hotspot 3 He/ 4 He ratios coincides with a domain of anomalously low seismic velocities at the underlying core-mantle boundary, and indicates that the provenance of high- 3 He/ 4 He magmas in the Manus Basin (and possibly elsewhere) is linked to this boundary layer—either by plume entrainment of lower mantle or, more speculatively, through addition of material from the core-mantle boundary.

  • High 3He/4He ratios in the Manus Backarc Basin: Implications for mantle mixing and the origin of plumes in the western Pacific Ocean
    Geology, 1998
    Co-Authors: Colin G. Macpherson, David R. Hilton, John M. Sinton, R. J. Poreda, Harmon Craig
    Abstract:

    Helium isotope ratios in oceanic glasses provide a high-integrity tracer of contributions from mantle plumes. Despite a diverse array of petrogenetic affinities, glasses from the central part of the Manus Basin—a Backarc Basin in the western Pacific—have typical plume (or hotspot) 3 He/ 4 He ratios that cluster around 12.2 R A (±1.0 R A n =18, where R A = 3 He/ 4 He of air), a value significantly higher than the range found in most mid-ocean-ridge basalts (MORB) ([8 ± 1] A ). Lavas in other parts of the Basin have MORB-like or lower 3 He/ 4 He values. A wide range of He concentrations characterizes the Manus Basin glasses: This is considered to reflect the high water content of some lavas, which promotes He loss through volatile degassing. For the most part, it is the degassed lavas that do not show the plume He isotope signature. Results of the present study, together with 3 He/ 4 He data for lavas and gases from islands to the south and east of the Bismark Sea, indicate that the focus of mantle plume upwelling is either the center of the Manus Basin or possibly the region to the northwest beneath the volcanic islands of the St. Andrew Strait. This region of plume or hotspot 3 He/ 4 He ratios coincides with a domain of anomalously low seismic velocities at the underlying core-mantle boundary, and indicates that the provenance of high- 3 He/ 4 He magmas in the Manus Basin (and possibly elsewhere) is linked to this boundary layer—either by plume entrainment of lower mantle or, more speculatively, through addition of material from the core-mantle boundary.