| 1. |
|
|
| 2. |
- Troll, Valentin R., et al.
(författare)
-
Crustal CO2 liberation during the 2006 eruption and earthquake events at Merapi volcano, Indonesia
- 2012
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39, s. L11302-
-
Tidskriftsartikel (refereegranskat)abstract
- High-temperature volcanic gas is widely considered to originate from ascending, mantle-derived magma. In volcanic arc systems, crustal inputs to magmatic gases mainly occur via subducted sediments in the mantle source region. Our data from Merapi volcano, Indonesia imply, however, that during the April-October 2006 eruption significant quantities of CO2 were added from shallow crustal sources. We show that prior to the 2006 events, summit fumarole gas delta C-13((CO2)) is virtually constant (delta C-13(1994-2005) = -4.1 +/- 0.3 parts per thousand), but during the 2006 eruption and after the shallow Yogyakarta earthquake of late May, 2006 (M6.4; hypocentres at 10-15 km depth), carbon isotope ratios increased to -2.4 +/- 0.2 parts per thousand. This rise in delta C-13 is consistent with considerable addition of crustal CO2 and coincided with an increase in eruptive intensity by a factor of similar to 3 to 5. We postulate that this shallow crustal volatile input supplemented the mantle-derived volatile flux at Merapi, intensifying and sustaining the 2006 eruption. Late-stage volatile additions from crustal contamination may thus provide a trigger for explosive eruptions independently of conventional magmatic processes.
|
|
| 3. |
|
|
| 4. |
- Berg, Sylvia, et al.
(författare)
-
Making Earth’s earliest continental crust : an analogue from voluminous Neogene silicic volcanism in NE-Iceland
- 2014
-
Konferensbidrag (refereegranskat)abstract
- Borgarfjörður Eystri in NE-Iceland represents the second-most voluminous exposure of silicic eruptive rocksin Iceland and is a superb example of bimodal volcanism (Bunsen-Daly gap), which represents a long-standingcontroversy that touches on the problem of crustal growth in early Earth. The silicic rocks in NE-Iceland approach25 % of the exposed rock mass in the region (Gústafsson et al., 1989), thus they significantly exceed the usual≤ 12 % in Iceland as a whole (e.g. Walker, 1966; Jonasson, 2007). The origin, significance, and duration of thevoluminous (> 300 km3) and dominantly explosive silicic activity in Borgarfjörður Eystri is not yet constrained(c.f. Gústafsson, 1992), leaving us unclear as to what causes silicic volcanism in otherwise basaltic provinces.Here we report SIMS zircon U-Pb ages and δ18O values from the region, which record the commencement ofsilicic igneous activity with rhyolite lavas at 13.5 to 12.8 Ma, closely followed by large caldera-forming ignimbriteeruptions from the Breiðavik and Dyrfjöll central volcanoes (12.4 Ma). Silicic activity ended abruptly with dacitelava at 12.1 Ma, defining a ≤ 1 Myr long window of silicic volcanism. Magma δ18O values estimated fromzircon range from 3.1 to 5.5 (± 0.3; n = 170) and indicate up to 45 % assimilation of a low-δ18O component (e.g.typically δ18O = 0 h Bindeman et al., 2012). A Neogene rift relocation (Martin et al., 2011) or the birth of anoff-rift zone to the east of the mature rift associated with a thermal/chemical pulse in the Iceland plume (Óskarsson& Riishuus, 2013), likely brought mantle-derived magma into contact with fertile hydrothermally-altered basalticcrust. The resulting interaction triggered large-scale crustal melting and generated mixed-origin silicic melts. Suchrapid formation of silicic magmas from sustained basaltic volcanism may serve as an analogue for generatingcontinental crust in a subduction–free early Earth (e.g. ≥ 3 Ga, Kamber et al., 2005).REFERENCES:Bindeman, I.N., et al., 2012. Terra Nova 24, 227–232.Gústafsson, L.E., et al., 1989. Jökull, v. 39, 75–89.Gústafsson, L.E., 1992. PhD dissertation, Freie Universität Berlin.Jonasson, K., 2007. Journal of Geodynamics, 43, 101–117.Kamber, B.S., et al., 2005. Earth Planet. Sci. Lett., Vol. 240 (2), 276-290.Martin, E., et al., 2011. Earth Planet. Sc. Lett., 311, 28–38.Óskarsson, B.V., & Riishuus, M.S., 2013. J. Volcanol. Geoth.Res., 267, 92–118.Walker, G.P.L., 1966. Bull. Volcanol., 29 (1), 375-402.
|
|
| 5. |
|
|
| 6. |
- Geiger, Harri, et al.
(författare)
-
Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions
- 2018
-
Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- The island of Bali in Indonesia is home to two active stratovolcanoes, Agung and Batur, but relatively little is known of their underlying magma plumbing systems. Here we define magma storage depths and isotopic evolution of the 1963 and 1974 eruptions using mineral-melt equilibrium thermobarometry and oxygen and helium isotopes in mineral separates. Olivine crystallised from a primitive magma and has average delta O-18 values of 4.8%. Clinopyroxene records magma storage at the crust-mantle boundary, and displays mantle-like isotope values for Helium (8.62 R-A) and delta O-18 (5.0-5.8%). Plagioclase reveals crystallisation in upper crustal storage reservoirs and shows delta O-18 values of 5.5-6.4%. Our new thermobarometry and isotope data thus corroborate earlier seismic and InSAR studies that inferred upper crustal magma storage in the region. This type of multi-level plumbing architecture could drive replenishing magma to rapid volatile saturation, thus increasing the likelihood of explosive eruptions and the consequent hazard potential for the population of Bali.
|
|
| 7. |
|
|
| 8. |
- Troll, Valentin, et al.
(författare)
-
Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption
- 2012
-
Ingår i: Solid Earth. - : Copernicus Publications. - 1869-9510 .- 1869-9529. ; 3:1, s. 97-110
-
Tidskriftsartikel (refereegranskat)abstract
- A submarine eruption started off the south coast of El Hierro, Canary Islands, on 10 October 2011 and continues at the time of this writing (February 2012). In the first days of the event, peculiar eruption products were found floating on the sea surface, drifting for long distances from the eruption site. These specimens, which have in the meantime been termed "restingolites" (after the close-by village of La Restinga), appeared as black volcanic "bombs" that exhibit cores of white and porous pumice-like material. Since their brief appearance, the nature and origin of these "floating stones" has been vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e. g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have analysed the textures and compositions of representative "restingolites" and compared the results to previous work on similar rocks found in the Canary Islands. Based on their high-silica content, the lack of igneous trace element signatures, the presence of remnant quartz crystals, jasper fragments and carbonate as well as wollastonite (derived from thermal overprint of carbonate) and their relatively high oxygen isotope values, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary layers that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate. As they are closely resembling pumice in appearance, but are xenolithic in origin, we refer to these rocks as "xeno-pumice". The El Hierro xeno-pumices hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies beneath the Canary Islands as well as in similar Atlantic islands that rest on sediment-covered ocean crust (e. g. Cape Verdes, Azores). The occurrence of "restingolites" indicates that crustal recycling is a relevant process in ocean islands, too, but does not herald the arrival of potentially explosive high-silica magma in the active plumbing system beneath El Hierro.
|
|
| 9. |
- Wiesmaier, Sebastian, et al.
(författare)
-
Magma mixing in the 1100 AD Montaña Reventada composite lava flow, Tenerife, Canary Islands : Interaction between rift zone and central volcano plumbing systems
- 2011
-
Ingår i: Contributions to Mineralogy and Petrology. - : Springer. - 0010-7999 .- 1432-0967. ; 162:3, s. 651-669
-
Tidskriftsartikel (refereegranskat)abstract
- Zoned eruption deposits commonly show a lower felsic and an upper mafic member, thought to reflect eruption from large, stratified magma chambers. In contrast, the Montaña Reventada composite flow (Tenerife) consists of a lower basanite and a much thicker upper phonolite. A sharp interface separates basanite and phonolite, and chilled margins at this contact indicate the basanite was still hot upon emplacement of the phonolite, i.e. the two magmas erupted in quick succession. Four types of mafic to intermediate inclusions are found in the phonolite. Inclusion textures comprise foamy quenched ones, others with chilled margins and yet others that are physically mingled, reflecting progressive mixing with a decreasing temperature contrast between the end-members. Analysis of basanite, phonolite and inclusions for majors, traces and Sr, Nd and Pb isotopes show the inclusions to be derived from binary mixing of basanite and phonolite end-members in ratios of 2:1 to 4:1. Although, basanite and phonolite magmas were in direct contact, contrasting 206Pb/204Pb ratios show that they are genetically distinct (19.7193(21)–19.7418(31) vs. 19.7671(18)–19.7807(23), respectively). We argue that the Montaña Reventada basanite and phonolite first met just prior to eruption and had limited interaction time only. Montaña Reventada erupted from the transition zone between two plumbing systems, the phonolitic Teide-Pico Viejo complex and the basanitic Northwest rift zone. A rift zone basanite dyke most likely intersected the previously emplaced phonolite magma chamber. This led to eruption of geochemically and texturally unaffected basanite, with the inclusion-rich phonolite subsequently following into the established conduit.
|
|
| 10. |
- Barker, Abigail, et al.
(författare)
-
Disequilibrium in historic volcanic rocks from Fogo, Cape Verde traces carbonatite metasomatism of recycled ocean crust
- 2023
-
Ingår i: Lithos. - : Elsevier. - 0024-4937 .- 1872-6143. ; , s. 107328-107328
-
Tidskriftsartikel (refereegranskat)abstract
- Fogo, Cape Verde, located upon thick oceanic lithosphere, provides a window into processes occurring in the mantle where recycled ocean crust in an upwelling mantle plume interacts with ambient mantle. Our objective is to investigate the nature of the lithologies of the mantle sources involved in the petrogenesis of historic volcanic rocks from Fogo. We observe enclaves and mingling textures in the lavas combined with oxygen isotope disequilibrium between olivine and clinopyroxene phenocrysts. Olivine δ18O values display positive correlations with Zr/Hf and Zr/Y and a negative correlation with U/Th, whereas clinopyroxene δ 18O values correlate positively with Ba/Nb. Heterogeneity between crystal populations and within the groundmass indicates that multiple magma batches are mixed beneath Fogo. In terms of mantle endmembers and source lithologies, a HIMU endmember was generated by melting of carbonated eclogite as indicated by low δ 18O values, Zr/Hf, Ba/Nb and high U/Th ratios. In contrast, we show the EM1 endmember has high δ 18O, Zr/Hf, Ba/Nb and low U/Th ratios, derived from melting of variably carbonated peridotite. Additionally, Ba/Th ratio are high, indicating that carbonatite melts have contributed to alkaline magma compositions at Fogo.
|
|
