Paleogeography of the West Burma Block and the eastern Neotethys Ocean: Constraints from Cenozoic sediments shed onto the Andaman-Nicobar ophiolites
P. C. BandopadhyayDouwe J.J. van HinsbergenDebaditya BandyopadhyayAlexis LichtEldert L. AdvokaatAlexis PlunderBiswajit GhoshArnab DasguptaJoão Trabucho‐Alexandre
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Abstract:
The Andaman and Nicobar ophiolites, in the forearc of the western Sunda subduction zone, underwent enigmatic, rapid Cenozoic vertical motions: shallow-water sediments with abundant arc debris characterize the middle Paleocene–middle Eocene and are under- and overlain by significantly deeper sediments. Recent paleomagnetic results revealed a near-equatorial paleolatitude of the West Burma Block and the associated subduction zone, at a similar latitude as the Andaman forearc until the early Eocene, providing a new avenue toward explaining the unusual stratigraphy. Here, we studied the provenance of the clastic sediments of the Andaman-Nicobar accretionary ridge using petrography, geochemistry, and detrital zircon geochronology. We found that the Paleocene-Eocene Namunagarh Grit is likely to be derived from a then proximal, 60 Ma old arc that was likely located in the ocean to the north (present-day east) of the West Burma Block, west of Andaman-Nicobar. The Oligocene–lower Miocene East Andaman Flysch contains West Burma Block debris that traveled much farther and mixed with sediments derived from Sundaland. The West Andaman and Great Nicobar Flysch have an additional Himalayan source consistent with derivation from the downgoing plate. We interpret this history as reflecting the late Paleocene–early Eocene collision of the West Burma Block, likely then part of the Australian Plate, with the Andaman forearc causing uplift and proximal sedimentation shed from the colliding arc. Subsequent northward motion of the West Burma Block caused subsidence of the Andaman forarc and N-S opening of the Andaman Sea, which opened a pathway for Sundaland-derived sediments to reach the Andaman ophiolites. The recently proposed high Cenozoic mobility of the West Burma Block remains to be reconciled in detail with geological observations in Myanmar and Sundaland, but our results show that this scenario provides ample opportunity to explain the previously enigmatic stratigraphic evolution of the Andaman and Nicobar Islands.Keywords:
Forearc
Flysch
Accretionary wedge
Detritus
For approximately 120 years since the beginning of European geology up to Ihe present day. Croatian geoscience has included intensive geological research of the Dinaridc Ophiolite zone. Research results can be grouped into several periods depending on the basic predominant approaches of European and World geology. ( 1) During the flysch period, ophiolites were spatially connected with the flysch formations. (2) During the geosynclinal period ophiolites were classified into the Diabas-Hornstein Formation'. (3) During the transitional period, characterized by the elaboration or the Basic Geological Map, a voluminous data were collected which could not be incorporated in geosynclinal ideas. (4) The last period is charactcrized by modern geodynamic interpretations resulting from global tectonics.
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Abstract. Multi‐channel seismic data obtained from the Nankai accretionary prism and forearc basin system has been studied to elucidate the migration and accumulation process of gas to the BGHS and examine the distribution pattern of BSRs and characteristic reflections associated with them. BSRs are distributed widely in the Nankai accretionary prism and associated forearc basins (33,000 km 2 ) and 90 % of them have migration and recycling origins. The widest distribution of the BSRs can be seen at the prism. A correlation between the BSR distributions and prism size shows that the BSRs tend to be more well‐developed in a prism of large size. This suggests that a large prism may produce much amount of gas‐bearing fluids that migrate to the BGHS and form the BSRs (tectonic control), hi the forearc basins, the BSRs are identified at topographic highs, anticlines and basin margins (structural control). The upward migration of gas‐bearing fluids is carried out through permeable sand layers and as a result, the distribution of BSRs is confined to alternating beds of sand and mud facies (sedimentary control). However, if there is enough time for upward migration and accumulation of gas to the BGHS, the BSRs can be generated widely in low‐permeable mud facies (time control). Those results imply that structural, tectonic, sedimentary and time controls are primary factors to decide the distribution of BSRs in the Nankai Trough area.
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The area from Andaman to northern Sumatran margin is a region where major faults collided that complicates the structural configuration. The origin of structures in the boundary between the accretionary wedge and forearc basin in the northwesternmost segment of the Sunda margin has been a subject of debates. This article reviews several published works on the Andaman – north Sumatran margin to characterize the boundary between forearc basin and accretionary wedge. Complex strain partitioning in this margin is characterized by sliver faults that crossing boundaries between the backarc basin, volcanic arc, forearc basin, and accretionary wedge. The fault zone can be divided into two segments: The West Andaman Fault (WAF) in the north and Simeulue Fault (SiF) in the southern part. A restraining step-over formed in between WAF and SiF. The SiF may extent onshore Simeulue to a strike-slip fault onshore. Strain-partitioning in such an oblique convergent margin appears to have formed a new deformation zone rather than reactivated the major rheological boundary in between the accretionary wedge and forearc basin. The eastern margin of the Andaman-north Sumatra accretionary wedge appears to have form as landward-vergent backthrusts of Diligent Fault (DF) and Nicobar Aceh Fault (NAF) rather than strike-slip faults. This characteristic appears to have formed in the similar way with the compressional structures dominated the eastern margin accretionary wedge of the central and south Sumatra forearc. Keywords: Andaman, North Sumatra, forearc, structure, accretionary wedge, strain partitioningDaerah Andaman - Sumatera bagian utara adalah wilayah di mana patahan-patahan besar saling bertemu dan membuat konfigurasi struktur menjadi rumit. Asal-usul struktur di batas antara prisma akresi dan cekungan busur muka di bagian paling baratlaut dari tepian Sunda telah menjadi topik perdebatan. Artikel ini mengulas beberapa studi yang telah diterbitkan sebelumnya mengenai tepian Andaman - Sumatra bagian utara untuk mengkarakterisasikan batas antara cekungan muka dan prisma akresi. Pemisahan regangan yang kompleks di tepian ini dicirikan oleh sliver fault yang melintasi batas antara cekungan busur belakang, busur vulkanik, cekungan busur muka, dan prisma akresi. Zona sesar tersebut dapat dibagi menjadi dua segmen, yaitu Sesar Andaman Barat (WAF) di utara dan Simeulue Fault (SiF) di bagian selatan. Sebuah restraining step-over terbentuk di antara WAF dan SiF. SiF kemungkinan menerus sampai ke Pulau Simeulue dan menyatu dengan sesar geser. Pemisahan regangan di tepian konvergen yang miring seperti itu tampaknya telah membentuk zona deformasi baru daripada mengaktifkan kembali batas reologi utama di antara prisma akresi dan cekungan busur muka. Batas bagian timur dari prisma akresi di Andaman – Sumatera bagian utara memiliki bentuk sebagai backthrusts berarah darat yaitu Sesar Diligent (DF) dan Sesar Nicobar Aceh (NAF) dan bukan merupakan sesar geser. Karakteristik ini tampaknya terbentuk dengan proses yang mirip dengan struktur-struktur kompresional yang mendominasi bagian timur prisma akresi di daerah Sumatra bagian tengah dan selatan.Kata kunci: Andaman, Sumatera bagian, busur muka, struktur, prisma akresi, pemisahan regangan
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The forearc crust along the Nankai Trough is characterized as an accretionary prism. The unconsolidated sediments on the subducting Philippine Sea plate are underplated to the southwest Japan arc, so that large amount of fluid is supplied to the accretionary prism. Such fluid could be related to various geological phenomena in the accretionary prism such as the accumulation of methane hydrate, expected as new energy resource. However, fluid distribution below the seafloor, in the forearc crust, had not been understood clearly. Marine magnetotelluric soundings around the Nankai Trough and the Kumano Basin were carried out in 2002-2003 to elucidate fluid distribution in the forearc crust. Both time series data of horizontal electric and magnetic fields were obtained at seven sites, and only electric field data were obtained at two sites. Apparent resistivity and impedance phase at each site were calculated from these observed data with removal of spike noises, and a resistivity model below the seafloor was estimated. The model resembles to a seismic reflection section. By interpreting the estimated model, fluid distribution in the accretionary prism and the upper oceanic crust is discussed: high fluid content within the accretionary prism is interpreted, especially along the splay fault. This result implies a pass way of fluid along the splay fault.
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Emplacement of ophiolitic rocks in forearc areas: Examples from central Japan and Izu-Mariana-Yap island arc system
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Abstract New whole‐rock major and trace element geochemistry from the Leka Ophiolite Complex in Norway is presented and compared to the geochemical evolution and proposed tectonomagmatic processes recorded in the Izu‐Bonin‐Mariana system. These data demonstrate that the Leka Ophiolite Complex formed as forearc lithosphere during subduction initiation. A new high‐precision zircon U‐Pb date on forearc basalt constrains the timing of subduction initiation in the “Leka sector” of the Iapetus Ocean to 491.36 ± 0.17 Ma. The tectonomagmatic record of the Leka Ophiolite Complex captures only the earliest stages of subduction initiation and is thereby distinct from some other Appalachian–Caledonian ophiolites of similar age. The diversity of Appalachian–Caledonian ophiolite records may represent differing preservation and exposure of a variable forearc lithosphere.
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The shape and morphology of the northern Barbados Ridge complex is largely controlled by the sediment yield and failure behavior in response to high lateral loads imposed by convergence.Loads in excess of sediment yield strength result in nonrecoverable deformations within the wedge, and failure strength acts as an upper limit beyond which stresses are released through thrust faults.Relatively high loading rates lead to delayed consolidation and in-situ pore pressures greater than hydrostatic.The sediment yield and failure behavior is described for any stress path by a generalized constitutive model.A yield locus delineates the onset of plastic (non-recoverable) deformation, as defined from the isotropic and anisotropic consolidation responses of high-quality 38-mm triaxial specimens; a failure envelope was obtained by shearing the same specimens in both triaxial compression and extension.The yield locus is shown to be rotated into extension space and is centered about a ^T-line greater than unity, suggesting that the in-situ major principal stress has rotated into the horizontal plane, and that the sediment wedge is being subjected to extensional effective stress paths.
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