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

Abstract. The variation in island arc magma production rates and their influencing mechanisms are of great significance since island arc magma is considered a main source of continental crust growth. The island arc magma directly originates from the molten mantle wedge, and the mantle melting is driven by fluids or melts from the subducted slab. Slab dehydration flux mainly depends on the slab thermal structures, and subducted slab melting requires a sufficiently high temperature. For the Aleutian subduction system, the subducted Pacific Plate has diverse thermal structures due to the existing fracture zones, ridges and slab window, so it is an ideal region for arc magma production rate research. However, the previous estimations are based on seismic profiles that only provide magma production rates at specific regions of the Aleutian arc, and these results are controversial. Here, we design a magma production rate estimation method based on gravity inversion constrained by deep seismic profiles. The first overview map of magma production rates along the Aleutian arc strike demonstrates that the magma production rates have the same trend as the slab dips, and the peaks correspond to the subduction of the fracture zones and ridges. The potential mechanisms for these correlations are as follows: (1) Slab water flux at subarc depths increases with increasing slab dip. More fluid flux would induce more mantle melting, and so the arc magma production rates are increased. (2) Water-rich serpentine is formed by hydrothermal alteration on or near the surface of the subducted slab when there are fracture zones. Serpentine decomposition at a depth of 80–120 km releases fluids in addition to the fluids released during normal slab dehydration. Therefore, more fluids induce more mantle melting and correspond a larger magma production rate. (3) The slab located in the Emperor Seamounts has a relatively high temperature and is also weak, so its melting is easier. Similarly, more slab melt means more mantle melt and a higher island arc magma production rate.

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The geochemistry of marine sediments, island arc magma genesis, and crust-mantle recycling

Earth and Planetary Science Letters ◽

10.1016/0012-821x(89)90079-4 ◽

1989 ◽

Vol 94 (1-2) ◽

pp. 1-21 ◽

Cited By ~ 526

Author(s):

Dalila Ben Othman ◽

William M. White ◽

Jonathan Patchett

Keyword(s):

Marine Sediments ◽

Island Arc ◽

Magma Genesis ◽

Arc Magma

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Geochemical Evolution of Akagi Volcano, NE Japan: Implications for Interaction Between Island-arc Magma and Lower Crust, and Generation of Isotopically Various Magmas

Journal of Petrology ◽

10.1093/petrology/42.12.2303 ◽

2001 ◽

Vol 42 (12) ◽

pp. 2303-2331 ◽

Cited By ~ 29

Author(s):

K. KOBAYASHI

Keyword(s):

Lower Crust ◽

Island Arc ◽

Geochemical Evolution ◽

Arc Magma ◽

Ne Japan

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LATE OLIGOCENE THOLEIITIC LAVA FROM KENANGA RIVER, TEGALOMBO PACITAN, EAST JAVA

Journal of Applied Geology ◽

10.22146/jag.6671 ◽

2009 ◽

Vol 1 (1) ◽

Author(s):

Dian Novia Sartika ◽

I Wayan Warmada ◽

Bhakti H. Harahap ◽

Widiasmoro Soewondo

Keyword(s):

Volcanic Rocks ◽

Parental Magma ◽

Volcanic Glass ◽

Island Arc ◽

Petrographic Analysis ◽

Late Oligocene ◽

Basaltic Composition ◽

Regional Tectonic ◽

Opaque Minerals ◽

Arc Magma

Watupatok Formation in Pacitan area consists of lava with basaltic composition and pillow structure. Kenanga river is only 5 km to southeast Watupatok village as type locality of this formation. Kenanga river’s lava were varying from diabasic with paving surface and columnar joint structure to basaltic composition with pillow structure. Lava were found as effusive flow and dike with sandstone inclusion. In field observation, lava exhibits strong porphiritic to aphyric texture, with vesicular to amygdaloidal structure. Plagioclase as phenocryst has mediumsized (2-4 mm) surrounded by volcanic glass as groundmass. Petrographic analysis shows intersertal to hyalophilitic texture, consist of plagioclase, pyroxene and opaque minerals as phenocryst and also groundmass together with volcanic glass. Seconday minerals are quartz, zeolite and calcite. Geochemichal analysis results indicate a low TiO2 (0.8– 0.9 wt.%), medium to high Al2O3 (14–17 wt.%), high Fe2O3 (10–12 wt.%) and low Mg value (Mg#) (39–42). According to TAS and AFM diagram, the rocks is apparently to be basalt and tholeiitic island arc magma. While spidergram pattern of the trace elements shows relatively flat fo HREE and enriched pattern on LREE. Niobium element displays a depleted anomaly, indicated that the crust influences in parental magma, which is another characteristic of magmatic island arc. Based on regional tectonic, the volcanic rocks from Late Oligocene in the area has relationship with subduction processes between Indo-Australia plate and Eurasian plate.Keywords: Pillow structure, tholeiitic, lava, subduction

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Petrogenesis of a rare Ediacaran tonalite–trondhjemite–granodiorite suite, Egypt, and implications for Neoproterozoic Gondwana assembly

Geological Magazine ◽

10.1017/s0016756820000795 ◽

2020 ◽

pp. 1-22

Author(s):

Abdel-Fattah M Abdel-Rahman

Keyword(s):

Island Arc ◽

Ionization Mass ◽

East African ◽

Wide Range ◽

Mantle Sources ◽

Nubian Shield ◽

East African Orogen ◽

Subducted Oceanic Crust ◽

Late Stages ◽

Arabian Nubian Shield

Abstract Most tonalite–trondhjemite–granodiorite (TTG) suites are Archean–Palaeoproterozoic in age, but those of Neoproterozoic–Phanerozoic age are scarce. A rare Ediacaran high-Al TTG suite has been identified at the Fannani Igneous Complex (FIC) in the northern Arabian–Nubian Shield, which is essentially composed of amalgamated Neoproterozoic island-arc Pan-African composite terranes that contain several ophiolitic sutures. The FIC exhibits a wide range of SiO2, Al2O3, Sr and Zr, shows moderate rare earth element (REE) enrichment, and K, Ti, Nb, Y and heavy REE depletion. It is a subsolvus suite with clear orogenic affinities and strong arc-geochemical signatures. The precise U–Pb zircon thermal ionization mass spectrometry age obtained (607.4 ± 1.95 Ma) indicates oceanic subduction extended to late stages of the East African Orogeny. The FIC exhibits 87Sr/86Sr compositions of 0.70346–0.71091 (Sr(i) ratio, 0.70284), and 143Nd/144Nd of 0.51254–0.51270 (ϵNd(t) = +5.12 to +7.16), typical of modern oceanic-arc rocks (as Japan-arc basalts), and suggestive of mantle sources and island-arc settings. The FIC possesses low values of Yb (1.55 ppm), Nb (14 ppm) and Y (24 ppm), and high ratios of Sr/Y (27), Zr/Sm (46) and Nb/Ta (11.8), typical of magmas produced by anatexis of a basaltic slab. Partial melting models show that the FIC magma was generated by melting (F = 0.25–0.50) of a subducted oceanic crust transformed into eclogite, leaving 10–25% garnet in the residue. The FIC and similar complexes produced via slab melting during the closure of the Mozambique Ocean formed large juvenile belts along the East African Orogen that sutured East and West Gondwana together into a united supercontinent.

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