The West Philippine Basin: An Eocene to early Oligocene back arc basin opened between two opposed subduction zones

We present geological, bulk-rock geochemical and Sr–Nd–Hf isotopic data for mafic rocks from the West Philippine Basin (WPB). These mafic rocks comprise pillow basalts characterized by a vesicular structure. The mid-ocean ridge basalt (MORB)-normalized trace element patterns of basalts from the study area display depletions in Nb. In addition, the chondrite-normalized lanthanide patterns of basalts from the WPB are characterized by significant depletions in the light lanthanides and nearly flat Eu to Lu segments. The investigated rocks have initial 87Sr/86Sr ratios (87Sr/86Sr(i)) of 0.703339–0.703455 and high εNd(t) values (8.0 to 8.7). Furthermore, basalts from the WPB have 176Hf/177Hf ratios that range from 0.28318 to 0.28321 and high εHf(t) from 15.2 to 16.3. Semi-quantitative modeling demonstrates that the parental melts of basalts from the study area were derived by ~20% adiabatic decompression melting of a rising spinel-bearing peridotite source. The Sr–Nd–Hf isotopic compositions of basalts from the WPB indicate that their parental magmas were derived from an upper mantle reservoir possessing the so-called Indian-type isotopic anomaly. Interpretation of the isotopic data suggests that the inferred mantle source was most likely influenced by minor inputs of a sediment melt derived from a downgoing lithospheric slab. Collectively, the petrographic and geochemical characteristics of basalts from the study area are analogous to those of mafic rocks with a back-arc basin (BAB)-like affinity. As such, the petrogenesis of basalts from the WPB can be linked to upwelling of an Indian-type mantle source due to lithospheric slab subduction that was followed by back-arc spreading.

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In Situ Geochemical Compositions of the Minerals in Basaltic Rocks from the West Philippine Basin: Constraints on Source Lithology and Magmatic Processes

Lithosphere ◽

10.2113/2020/8878501 ◽

2020 ◽

Vol 2020 (1) ◽

pp. 1-24

Author(s):

Long Yuan ◽

Quanshu Yan ◽

Yanguang Liu ◽

Shiying Wu ◽

Ruirui Wang ◽

...

Keyword(s):

Mantle Plume ◽

Spreading Center ◽

Minor Amount ◽

The West ◽

Basaltic Rocks ◽

West Philippine Basin ◽

Geological Evolution ◽

Magmatic Processes ◽

Back Arc

Abstract Since the early Cenozoic, the West Philippine Basin (WPB) and the whole Philippine Sea Plate (PSP) has undergone a complex geological evolution. In this study, we presented K-Ar ages, in situ trace element, and major element compositions of minerals of basalts collected from the Benham Rise and the Central Basin Fault (CBF) in the WPB, to constrain their magmatic process and regional geological evolution. Olivine phenocrysts and microlites in the alkali basalts (20.9 Ma) from the Benham Rise have forsterite (Fo) contents of 56.90%–76.10% and 53.13%-66.41%, respectively. The clinopyroxenes in the tholeiites (29.1 Ma) from the CBF is predominantly diopside and augite, and it is depleted in light rare earth elements (LREEs) (LaN/YbN=0.13–3.40) and large-ion lithophile elements (LILEs). The plagioclases in the basalts from both of the Benham Rise and the CBF are predominantly labradorite and andesine, with a minor amount of bytownite, and it is enriched in LREEs, Ba, Sr, and Pb and exhibits strong positive Eu anomalies. However, there exist obvious differences in plagioclase compositions between these two tectonic sites. The source lithology of the Benham Rise basaltic rocks could be garnet pyroxenite, and yet that of the CBF could be spinel-lherzolite. The calculated mantle potential temperature beneath the Benham Rise is 1439°C–1473°C, which is significantly higher than that beneath the CBF (1345°C–1381°C), suggesting there existed thermal anomaly beneath the Rise during basaltic magmatism. This study also calculated the temperature and pressure of the clinopyroxenes and plagioclases, which have been used to indicate magmatic processes. Finally, we suggest that the Benham Rise basaltic rocks may be related to a mantle plume (e.g., the Oki-Daito mantle plume), and the CBF was once located in a back-arc spreading center behind an active subduction zone. The extinction of the Oki-Daito mantle plume activity might be at about 20.9 Ma, and cessation of the back-arc spreading of WPB was at about 29.1 Ma or younger.

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Diatom distribution as an environmental indicator in surface sediments of the West Philippine Basin

Chinese Journal of Oceanology and Limnology ◽

10.1007/s00343-016-5306-8 ◽

2016 ◽

Vol 35 (2) ◽

pp. 431-443 ◽

Cited By ~ 3

Author(s):

Linnan Shen ◽

Min Chen ◽

Binbin Lan ◽

Hongshuai Qi ◽

Aimei Zhang ◽

...

Keyword(s):

Surface Sediments ◽

Environmental Indicator ◽

The West ◽

West Philippine Basin

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Opening and closure of Iranian back-arc basins: A seismic tomography view

10.5194/egusphere-egu21-5209 ◽

2021 ◽

Author(s):

Nalan Lom ◽

Abdul Qayyum ◽

Derya Gürer ◽

Douwe G. van der Meer ◽

Wim Spakman ◽

...

Keyword(s):

Seismic Tomography ◽

Subduction Zones ◽

Three Dimensional ◽

Plate Motion ◽

Limited Information ◽

Three Dimensional Model ◽

Slab Geometry ◽

Novel Approach ◽

Sanandaj Sirjan Zone ◽

Back Arc

<p>Iran is a mosaic of continental blocks that are surrounded by Tethyan oceanic relics. Remnants of these oceanic rock assemblages are exposed around the Central Iranian Microcontinent (CIM), discretely along the Sanandaj-Sirjan Zone and in Jaz-Murian. The ophiolite belts surrounding the CIM are mainly assumed to represent narrow back-arc basins that opened in Cretaceous and closed before the Eocene. Although these ophiolites are exposed as small pieces on continental crust today, they represent oceans wide enough to form supra-subduction ophiolites and arc-related magmatic rocks which suggest that their palaeogeographic width was at least some hundreds of kilometers. Current models for the palaeogeographic dimension, opening and closure of these basins are highly schematic. They usually seem plausible in two-dimensional reconstructions, however a single three-dimensional model explaining whole Iran and its surrounding regions has not been fully accomplished.&#160; This is mostly because while the geological record provides constraints on the origin and ages of the subducted ocean floor, it provides limited information about onset and cessation of the subduction and almost no constraints on the dimension of these oceans and the subduction zones that consumed them.</p><p>In this study, we follow a novel approach in estimating the dimension and evolution of these back-arc basin by using seismic tomography. Seismic tomography has revealed that we can image and trace subducted lithosphere relics. Imaged mantle structure is now being used to link sinking slabs with sutures and to define shape of a slab. Systematic comparison of regions where the timing of subduction is reasonably well constrained by geological data showed that slabs sink gradually through the mantle at rates more or less the same. This perspective enabled us to study slab shape as a function of absolute trench motion. While mantle stationary trenches tend to create steep slabs or slab walls, the flat-lying segments are formed where the overlying trenches are mobile relative to the mantle, normal facing during roll-back, overturned during slab advance. &#160;Under the assumption of vertical sinking after break-off, it is also possible to locate the palaeo-trenches. &#160;When combined with absolute plate motion reconstructions, tomographically determined volume and size of the subducted lithosphere can also be used to estimate the size/width of the prehistoric oceans. To this end, we build on and further develop concepts that relate absolute trench motion during subduction to modern slab geometry to evaluate the possible range of dimensions associated with opening and closure of the Iranian back-arc basins.</p>

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Early Oligocene chinchilloid caviomorphs from Puerto Rico and the initial rodent colonization of the West Indies

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2019.2806 ◽

2020 ◽

Vol 287 (1920) ◽

pp. 20192806 ◽

Cited By ~ 4

Author(s):

Laurent Marivaux ◽

Jorge Vélez-Juarbe ◽

Gilles Merzeraud ◽

François Pujos ◽

Lázaro W. Viñola López ◽

...

Keyword(s):

Puerto Rico ◽

West Indies ◽

Distinct Species ◽

South American ◽

The West ◽

Early Oligocene ◽

Biogeographic History ◽

Phylogenetic Affinities ◽

Dispersal Events ◽

South American Origin

By their past and present diversity, rodents are among the richest components of Caribbean land mammals. Many of these became extinct recently. Causes of their extirpation, their phylogenetic affinities, the timing of their arrival in the West Indies and their biogeographic history are all ongoing debated issues. Here, we report the discovery of dental remains from Lower Oligocene deposits ( ca 29.5 Ma) of Puerto Rico. Their morphology attests to the presence of two distinct species of chinchilloid caviomorphs, closely related to dinomyids in a phylogenetic analysis, and thus of undisputable South American origin. These fossils represent the earliest Caribbean rodents known thus far. They could extend back to 30 Ma the lineages of some recently extinct Caribbean giant rodents ( Elasmodontomys and Amblyrhiza ), which are also retrieved here as chinchilloids. This new find has substantial biogeographic implications because it demonstrates an early dispersal of land mammals from South America to the West Indies, perhaps via the emergence of the Aves Ridge that occurred ca 35–33 Ma (GAARlandia hypothesis). Considering both this new palaeontological evidence and recent molecular divergence estimates, the natural colonization of the West Indies by rodents probably occurred through multiple and time-staggered dispersal events (chinchilloids, then echimyid octodontoids (spiny rats/hutias), caviids and lastly oryzomyin muroids (rice rats)).

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The Origin of Back-Arc Spreading in The Eastern Edge of Scotia Plate

BULETIN OSEANOGRAFI MARINA ◽

10.14710/buloma.v5i1.11292 ◽

2016 ◽

Vol 5 (1) ◽

pp. 21

Author(s):

Indra Budi Prasetyawan

Keyword(s):

Subduction Zones ◽

Sandwich Plate ◽

Magnetic Anomalies ◽

South American ◽

The South ◽

Origin And Evolution ◽

Bathymetric Data ◽

Scotia Ridge ◽

Back Arc ◽

Eastern Edge

The origin and evolution of back-arc spreading in the eastern edge of Scotia Plate will be discussed in this paper. The Scotia Plate is a tectonicplate on the edge of the South Atlantic and Southern Ocean, located between the South American and Antartic plates. The East Scotia Ridge (ESR) in the eastern edge of Scotia Plate, forned due to subduction of the South American plate beneath the South Sandwich plate along the South Sandwich Island arc. The methods and techniques of data acquisition used were data from absolution motions and data from magnetic anomalies and bathymetric data. Magnetic anomalies and bathymetric data that used in this paper consist of two sets data. First, magnetic anomalies and bathymetric data which were obtained by aboard HMS Endurance in the 1969-70 austral summer, and the second, magnetic anomalies and bathymetric data which were obtained after removal of the International Geomagnetic Reference Field (IGRF). Absolution motion analyses in the subduction zones of Sandwich plate results that form back-arc spreading in East Scotia Ridge showing high deformation for slow moving upper plates. Where back-arc spreading is associated with upper plate retreat that reaches 26.9 mm/year and have back-arc deformation style consistent with upper plate absolute. Key Words: Geological oceanography, Scotia plate, back-arc spreading

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Ophiolitic Pyroxenites Record Boninite Percolation in Subduction Zone Mantle

Minerals ◽

10.3390/min9090565 ◽

2019 ◽

Vol 9 (9) ◽

pp. 565 ◽

Cited By ~ 2

Author(s):

Véronique Le Roux ◽

Yan Liang

Keyword(s):

Subduction Zone ◽

Subduction Zones ◽

Mantle Wedge ◽

Major Element ◽

Early Stage ◽

Diffusion Modeling ◽

Melt Infiltration ◽

Melt Percolation ◽

Back Arc ◽

Parental Melts

The peridotite section of supra-subduction zone ophiolites is often crosscut by pyroxenite veins, reflecting the variety of melts that percolate through the mantle wedge, react, and eventually crystallize in the shallow lithospheric mantle. Understanding the nature of parental melts and the timing of formation of these pyroxenites provides unique constraints on melt infiltration processes that may occur in active subduction zones. This study deciphers the processes of orthopyroxenite and clinopyroxenite formation in the Josephine ophiolite (USA), using new trace and major element analyses of pyroxenite minerals, closure temperatures, elemental profiles, diffusion modeling, and equilibrium melt calculations. We show that multiple melt percolation events are required to explain the variable chemistry of peridotite-hosted pyroxenite veins, consistent with previous observations in the xenolith record. We argue that the Josephine ophiolite evolved in conditions intermediate between back-arc and sub-arc. Clinopyroxenites formed at an early stage of ophiolite formation from percolation of high-Ca boninites. Several million years later, and shortly before exhumation, orthopyroxenites formed through remelting of the Josephine harzburgites through percolation of ultra-depleted low-Ca boninites. Thus, we support the hypothesis that multiple types of boninites can be created at different stages of arc formation and that ophiolitic pyroxenites uniquely record the timing of boninite percolation in subduction zone mantle.

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The palaeoproterozoic (Birimian) of Haute-Comoé in the West African craton, Ivory Coast: a transtensional back-arc basin

Precambrian Research ◽

10.1016/0301-9268(94)90106-6 ◽

1994 ◽

Vol 65 (1-4) ◽

pp. 207-229 ◽

Cited By ~ 55

Author(s):

M. Vidal ◽

G. Alric

Keyword(s):

Ivory Coast ◽

West African ◽

The West ◽

West African Craton ◽

Back Arc

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The geology and evolution of the Pinchi Fault Zone at Pinchi Lake, central British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e77-120 ◽

1977 ◽

Vol 14 (6) ◽

pp. 1324-1342 ◽

Cited By ~ 17

Author(s):

I. A. Paterson

Keyword(s):

Fault Zone ◽

Subduction Zones ◽

High Pressures ◽

Metamorphic Grade ◽

Fault System ◽

Late Triassic ◽

Transform Fault ◽

The West ◽

Early Mesozoic ◽

Complex Fault

At Pinchi Lake, the Pinchi Fault Zone separates the early Mesozoic Takla Group to the east from the late Paleozoic Cache Creek Group to the west. Between these regions a complex fault system involves a series of elongate fault-bounded blocks of contrasting lithology and metamorphic grade. These blocks consist of: (a) highly deformed aragonite–dolomite limestone and blueschist, (b) pumpellyite–aragonite greenstone, (c) a harzburgite–gabbro–diabase–basalt ophiolite sequence, (d) serpentinized alpine ultramafite, and (e) Cretaceous (?) conglomerate. The blueschist probably formed at 8–12 kbar (8 × 105–12 × 105 kPa) and 225–325 °C during a penetrative early deformation which was closely followed by a later deformation associated with a Late Triassic uplift and cooling event. The ophiolite sequence is overlain by Late Triassic sediments which locally contain aragonite suggesting that at least part of the Takla Group may have also undergone high pressure – low temperature metamorphism.The evolution of the 450 km fault zone is discussed and a model is proposed which involves right lateral transform faulting on the Pinchi Fault and underthrusting along northerly dipping subduction zones during the Late Triassic. The blueschist formed at high pressures in such a subduction zone and leaked to the surface in zones of low pressure along an active transform fault.

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