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Complex origin for the south-western Zamboanga metamorphic basement complex, Western Mindanao, Philippines (2000)

Tamayo, Rodolfo A. ; Yumul, Graciano P. ; Maury, René C. ; [et al.]

Melbourne, Australia : Blackwell Science Pty

The @island arc 9 (2000), S. 0

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ISSN: 1440-1738

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Abstract Amphibolites unconformably overlain by a metasedimentary sequence of quartz-muscovite-feldspar-kyanite schists, metagraywackes and epidote-bearing amphibolites occur in the northern portion of the south-western Zamboanga metamorphic basement complex, western Mindanao. These amphibolites (here identified as the Mount Dansalan amphibolites) display relict magmatic textures inherited from cumulate gabbro protoliths. Bulk-rock major and trace-element data are consistent with this hypothesis. Together with the chemistry of relict igneous clinopyroxenes, they indicate a magmatic arc-related signature for the gabbro protoliths. Geochemical data allow us to identify various sources for the associated metasediments: the gabbro themselves for the metagraywackes and a continental basement for the quartz-muscovite-feldspar-kyanite schists. Both sources contributed to the genesis of the epidote-amphibolite metasediments. The compositions of the metamorphic mineral assemblages suggest that the rocks have undergone metamorphism at temperatures ranging from 550°C to 700°C and pressures probably in the range of 5–9 kbar. 40K–40Ar isotopic study of amphibole separates from the Mount Dansalan samples document a metamorphic event dated at 24.6 ± 1.4, 22.2 ± 1.4 and 21.2 ± 1.2 Ma. Our results are in agreement with plate tectonic models which describe the south-western Zamboanga metamorphic basement as a continental terrane. However, its evolution was not as simple as it was usually considered. In particular the basement incorporated slivers of magmatic arc crust, which cannot be unambiguously related to any of the Tertiary arcs documented in the area.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1440-1738.2000.00308.x

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2

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Behavior of Niobium, Tantalum and other high field strength elements in adakites and related lavas from The Philippines (2000)

Prouteau, Gaëlle ; Maury, René C. ; Sajona, Fernando G. ; [et al.]

Melbourne, Australia : Blackwell Science Pty

The @island arc 9 (2000), S. 0

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ISSN: 1440-1738

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Abstract Pliocene–Quaternary adakites and spatially and temporally associated niobium-enriched basalts (the latter thought to be derived by melting of slab melt-metasomatized mantle) from the Philippine island arcs have been selected for analysis of high field strength elements (HFSE). All these samples have nearly constant and chondritic Zr/Hf ratio (36.5) and slightly infrachondritic Nb/Ta ratio (14.7). We interpret adakitic magmas to be derived from the partial melting at approximately 900°C of subducted mid-ocean ridge basalts (MORB) crust, with rutile and/or ilmenite as residual minerals. Melting calculations show that, under these conditions, slab melts should have suprachondritic Nb/Ta ratios. The obvious discrepancy with our data is attributed to insufficient knowledge of rutile-melt partition coefficients for HFSE. Consequently, abnormal Nb/Ta or Zr/Hf ratios cannot be considered as potential markers of slab melting processes in island arcs.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1440-1738.2000.00296.x

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3

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Slab melt as metasomatic agent in island arc magma mantle sources, Negros and Batan (Philippines) (2000)

Sajona, Fernando G. ; Maury, Rene C. ; Prouteau, Gaëlle ; [et al.]

Melbourne, Australia : Blackwell Science Pty

The @island arc 9 (2000), S. 0

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ISSN: 1440-1738

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Abstract Two new cases of association of adakites with ‘normal’ island arc lavas and transitional adakites are recognized in the islands of Batan and Negros in northern and central Philippines, respectively. The Batan lavas are related to the subduction of the middle Miocene portion of the South China Sea basin along the Manila trench; those of Negros come from the almost aseismic subduction of the middle Miocene Sulu Sea crust along the Negros trench. The occurrence of the Batan adakites is consistent with previous findings showing adakitic glass inclusions within minerals of mantle xenoliths associated with Batan arc lavas. The similarity of adakite ages (1.09 Ma) and that of the metasomatized xenoliths (1 Ma) suggests that both are linked to the same slab-melting and metasomatic event. Earlier Sr, Pb and Nd-isotopic studies, however, also reveal the presence of an important sediment contribution to the Batan lava geochemistry. Thus, the role played by slab melts, assumed to have mid-ocean ridge basalts-like (MORB) isotopic characteristics, in enriching the Batan subarc mantle is largely masked by the sediment input. The Negros adakites are present only in Mount Cuernos, the volcanic center nearest to the Negros trench. Batch partial melting calculations show that the Negros adakites could be derived from a garnet amphibolitic source with normal-MORB (N-MORB) geochemistry. This is supported by the MORB-like isotopic characteristics of the Mount Cuernos lavas. The volcanic rocks from the other volcanoes consist of normal arc and transitional adakitic lavas that have slightly higher Sr- and Pb-isotopic ratios, probably due to slight sediment input. Mixing of adakites and normal arc lavas to produce transitional adakites is only partly supported by trace element geochemistry and not by field evidence. The transitional adakites can be modeled as partial melts of an adakite-enriched mantle. Trace element enrichment of non-adakitic lavas could reflect the interaction of their mantle source with uprising slab melts, as metasomatic mantle minerals scavenge certain trace elements from the adakitic fluids. Therefore, in arcs beneath which thick (up to 2 km) continent-derived detrital sediments are involved in subduction, like in Batan, the sediment signature can overwhelm the slab melt input. In arcs like Negros where slow subduction could cause a more efficient scraping of thinner (approximately 1 km) detrital sediments, the contribution of slab melts is easier to detect.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1440-1738.2000.00295.x

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4

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Collision, subduction and accretion events in the Philippines: A synthesis (2003)

Yumul, Graciano P. ; Dimalanta, Carla B. ; Tamayo, Rodolfo A. ; [et al.]

Melbourne, Australia : Blackwell Science Pty

The @island arc 12 (2003), S. 0

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ISSN: 1440-1738

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Abstract The Philippines preserves evidence of the superimposition of tectonic processes in ancient and present-day collision and subduction zone complexes. The Baguio District in northern Luzon, the Palawan–Central Philippine region and the Mati–Pujada area in southeastern Mindanao resulted from events related to subduction polarity reversal leading to trench initiation, continent-arc collision and autochthonous oceanic lithosphere emplacement, respectively. Geological data on the Baguio District in Northern Luzon reveal an Early Miocene trench initiation for the east-dipping Manila Trench. This followed the Late Oligocene cessation of subduction along the west-dipping proto-East Luzon Trough. The Manila Trench initiation, which is modeled as a consequence of the counter-clockwise rotation of Luzon, is attributed to the collision of the Palawan microcontinental block with the Philippine Mobile Belt. In the course of rotation, Luzon onramped the South China Sea crust, effectively converting the shear zone that bounded them into a subduction zone. Several collision-related accretionary complexes (e.g. Romblon, Mindoro) are present in the Palawan–Central Philippine region. The easternmost collision zone boundary is located east of the Romblon group of islands. The Early Miocene southwestward shift of the collision boundary from Romblon to Mindoro started to end by the Pliocene. Continuous interaction between the Palawan microcontinental block and the Philippine Mobile Belt is presently taken up again along the collisional boundary east of the Romblon group of islands. The Mati–Pujada Peninsula area, on the other hand, is underlain by the Upper Cretaceous Pujada Ophiolite. This supra-subduction zone ophiolite is capped by chert and pelagic limestones which suggests its derivation from a relatively deep marginal basin. The Pujada Ophiolite could be a part of a proto-Molucca Sea plate. The re-interpretation of the geology and tectonic settings of the three areas reaffirm the complex geodynamic evolution of the Philippine archipelago and addresses some of its perceived geological enigmas.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1440-1738.2003.00382.x

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5

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Metasomatism of the sub-arc mantle inferred from trace elements in Philippine xenoliths (1992)

Maury, René C. ; Defant, Marc J. ; Joron, Jean-Louis

[s.l.] : Nature Publishing Group

Nature 360 (1992), S. 661-663

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] The Luzon arc formed from the eastward subduction of the South China Sea oceanic lithosphere beneath the Philippines. Geochemical studies10"12 have detected latitudinal variations along the strike of the arc which have been attributed to source enrichment through the contribution of subducted ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/360661a0

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6

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Segregation structures in vapor-differentiated basaltic flows (2000)

Caroff, Martial ; Maury, René C. ; Cotten, Joseph ; [et al.]

Springer

Bulletin of volcanology 62 (2000), S. 171-187

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ISSN: 1432-0819

Keywords: Key words Lava flows ; Vesicle cylinders ; Segregation sheets ; Segregation vesicles ; Water oversaturation ; Ocean island basalts ; Flood basalts

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Vesicle cylinders represent a spectacular kind of segregation structure involving residual liquids formed in situ during the cooling of lava flows. These vertical pipes, commonly found within basalt flows typically 2–10 m thick, are interpreted as the product of a vapor-driven differentiation process. The olivine phenocrysts and the earliest generation of groundmass olivines found in cylinder-bearing basalts appear to have been generally affected by magmatic oxidation, resulting in high-temperature iddingsite (HTI) alteration. This feature is also observed within cylinder-free basalt flows which exhibit other kinds of vesicular segregation structures, such as vesicle-rich pegmatoid segregation sheets and/or segregation vesicles. Detailed textural, petrological, and geochemical characteristics of two types of cylinders, three types of vesicle sheets, and five types of segregation vesicles are described, based on the study of 12 occurrences of HTI-bearing basalt flows from oceanic shield volcanoes or continental basalt plateaus. We propose a general classification of these segregation structures likely to derive from vapor differentiation. Flow thickness is probably the main factor influencing their morphology. Finally, we suggest that the concomitant occurrence of olivine oxidation and vapor-differentiation effects results from the late persistence of water oversaturation after eruption, perhaps due to a high rate of magma ascent.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004450000077

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7

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Partial melting below Tubuai (Austral Islands, French Polynesia) (1997)

Caroff, Martial ; Maury, René C. ; Guille, Gérard ; [et al.]

Springer

Contributions to mineralogy and petrology 127 (1997), S. 369-382

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Process identification diagrams based on trace element data show that mafic lavas from Tubuai, including alkali basalts, basanites, analcitites and nephelinites, result from different degrees of partial melting of an isotopically homogeneous mantle source. Our fractionation-corrected data are consistent with a batch melting model or a dynamic melting model involving a threshold value for melt separation close to 1% and degrees of melting ranging from 5–8% (alkali basalts) to 1.5–3% (nephelinites). The relative source concentration pattern, calculated using an inverse numerical method, shows an enrichment in highly incompatible elements. We propose that the Tubuai lava suite was derived from a two-stage partial melting process. Melting first affected the plume material located within the transition zone between garnet and spinel domains, producing alkali basalts and basanites. Then, the melting zone migrated upwards to the base of the overlying spinel-bearing lithospheric mantle, producing highly silica-undersaturated lavas. The lower lithosphere had previously been enriched by intrusion of pyroxenite veins representing plume-derived melts which percolated away from the main magma conduits.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004100050286

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8

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Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano, Panama (1991)

Defant, Mare J. ; Clark, Lee F. ; Stewart, Robert H. ; [et al.]

Springer

Contributions to mineralogy and petrology 106 (1991), S. 309-324

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ISSN: 1432-0967

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract The easternmost stratovolcano along the Central American arc is El Valle volcano, Panama. Several andesitic and dacitic lava flows, which range in age 5–10 Ma, are termed the old group. After a long period of quiescence (approximately 3.4 Ma), volcanic activity resumed approximately 1.55 Ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows 0.9–0.2 Ma. These are referred to as the young group. All of the samples analyzed are calc-alkaline andesites and dacites. The mineralogy of the two groups is distinct; two pyroxenes occur in the old-group rocks but are commonly absent in the young group. In contrast, amphibole has been found only in the young-group samples. Several disequilibrium features have been observed in the minerals (e.g., oscillatory zoning within clinopyroxenes). These disequilibrium textures appear to be more prevalent among the old- as compared with the young-group samples and are most likely the result of magma-mixing, assimilation, and/or polybaric crystallization. Mass-balance fractionation models for major and trace elements were successful in relating samples from the old group but failed to show a relationship among the young-group rocks or between the old- and young-group volcanics. We believe that the old-group volcanics were derived through differentiation processes from basaltic magmas generated within the mantlewedge. The young group, however, does not appear to be related to more primitive magmas by differentiation. The young-group samples cannot be related by fractionation including realistic amounts of amphibole. Distinctive geochemical features of the young group, including La/Yb ratios〉15, Yb〈1, Sr/Y〉150, and Y〈6, suggest that these rocks were derived from the partial melting of the subducted lithosphere. These characteristics can be explained by the partial melting of a source with residual garnet and amphibole. Dacitic material with the geochemical characteristics of subducted-lithosphere melting is generated apparently only where relatively hot crust is subducted, based on recent work. The young dacite-genesis at El Valle volcano is related to the subduction of relatively hot lithosphere.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00324560

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Geology of the Zamboanga Peninsula, Mindanao, Philippines: an enigmatic South China continental fragment? (2007)

Yumul, Graciano P., Jr ; Dimalanta, Carla B. ; Tamayo, Rodolfo A., Jr ; [et al.]

In: Geological Society Special Publication 226: 289-312.

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Publication Date: 2007-10-08

Description: Mindanao Island in the southern Philippines is made up of two blocks: the island-arc-related eastern-central Mindanao block and the continental Zamboanga Peninsula, which contains several ophiolitic bodies and melanges. The Middle Miocene Siayan-Sindangan Suture Zone represents the tectonic boundary between the island-arc and continental blocks. A Middle Miocene age of collision is interpreted from the unconformity between the Late Miocene Motibot Formation and the underlying Middle Miocene Gunyan Melange, which serves as basement to the suture zone. The Middle Miocene Siayan-Sindangan Suture Zone was formerly a subduction zone complex that was reactivated as a sinistral strikeslip fault following the collision of eastern-central Mindanao with the Zamboanga Peninsula. New 40K-40Ar whole-rock dating of lava flows from the Zamboanga Peninsula has revealed Middle to Late Miocene ages, which is consistent with the possible existence of an Early Miocene Sulu Trench. The possibility that the Zamboanga Peninsula could be part of the Palawan microcontinental block has been forwarded by previous workers, due to their similarity in stratigraphy, geological structure and metamorphic rock suites. The Palawan microcontinental block separated from southern China during the opening of the South China Sea in Oligo-Miocene times. If indeed the Zamboanga Peninsula was once part of Palawan, it represents the southernmost part of the rifted southeastern China continental margin.

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