Voluminous arc dacites as amphibole reaction-boundary liquids

Blatter, Dawnika L.; Sisson, T. W.; Hankins, W. B.

doi:10.1007/s00410-017-1340-6

Cited by 76 publications

(52 citation statements)

References 87 publications

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“…A detailed assessment of the role of amphibole in generating the (rhyo)dacites on Nisyros is outside the scope of this work. We do note, however, the striking resemblance in lithology between the Type 3 cumulates and the hornblende-gabbroic assemblage found to be in equilibrium with Mount St. Helens dacites (Blatter et al 2017). This study demonstrates that porphyritic dacites, compositionally and texturally similar to the Nisyros HPRD suite, are multiply saturated in plagioclase, pyroxene, amphibole and magnetite at 0.7 GPa and form along a peritectic reaction involving amphibole and clinopyroxene.…”

Section: A Deep or Shallow Amphibole Sponge?mentioning

confidence: 95%

“…Derivative melts formed by the fractionation of Type 2 cumulates will have lower Mg# and higher H 2 O contents than primitive melts and will, upon ascent and water saturation, crystallise the common Type 1 cumulates. In the lower crust, Type 2 cumulates will mature to Type 3 hornblende-gabbros and plagioclase-hornblendites along a peritectic reaction in which clinopyroxene is consumed and amphibole and dacitic melt are generated (e.g., Blatter et al 2017). The latter is a prime candidate to feed a shallow (rhyo)dacitic mush system that, upon reactivation by mafic melts, can be erupted as porphyritic, enclave-bearing domes and lava flows of the HPRD suite (this study; Braschi et al 2012Braschi et al , 2014Zouzias and St Seymour 2014).…”

Section: Synthesis: Structure Of Nisyros' Plumbing Systemmentioning

confidence: 99%

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A mineral and cumulate perspective to magma differentiation at Nisyros volcano, Aegean arc

Klaver

Matveev

Berndt

et al. 2017

Contrib Mineral Petrol

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and these appear to be derived from the lower crust (0.5-0.8 GPa). The suppressed stability of plagioclase and early saturation of amphibole in these cumulates are indicative of high-pressure crystallisation from primitive hydrous melts (≥ 3 wt% H 2 O). Clinopyroxene in these cumulates has Al 2 O 3 contents up to 9 wt% due to the absence of crystallising plagioclase, and is subsequently consumed in a peritectic reaction to form primitive, Al-rich amphibole (Mg# > 73, 12-15 wt% Al 2 O 3 ). The composition of these peritectic amphiboles is distinct from trace element-enriched interstitial amphibole in shallower cumulates. Phenocryst compositions and assemblages in both suites differ markedly from the cumulates. Phenocrysts, therefore, reflect shallow crystallisation and do not record magma differentiation in the deep arc crust.

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Section: A Deep or Shallow Amphibole Sponge?mentioning

confidence: 95%

Section: Synthesis: Structure Of Nisyros' Plumbing Systemmentioning

confidence: 99%

A mineral and cumulate perspective to magma differentiation at Nisyros volcano, Aegean arc

Klaver

Matveev

Berndt

et al. 2017

Contrib Mineral Petrol

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“…However, it is difficult to reconcile the abrupt disappearance of the continental Moho within 10-20 km of MSH with the notion that it is entirely controlled by mantle hydration. Hydrous phases such as serpentine and chlorite should be stable in the mantle wedge only at <800°C (reviewed in Abers et al, 2017), whereas MSH dacites equilibrated at 925-940°C in the lower crust (Blatter et al, 2017). Hydrous phases such as serpentine and chlorite should be stable in the mantle wedge only at <800°C (reviewed in Abers et al, 2017), whereas MSH dacites equilibrated at 925-940°C in the lower crust (Blatter et al, 2017).…”

Section: The North American Platementioning

confidence: 99%

Imaging Subduction Beneath Mount St. Helens: Implications for Slab Dehydration and Magma Transport

Mann

Abers

Crosbie

et al. 2019

Geophysical Research Letters

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Mount St. Helens (MSH) is anomalously 35–50 km trenchward of the main Cascade arc. To elucidate the source of this anomalous forearc volcanism, the teleseismic‐scattered wavefield is used to image beneath MSH with a dense broadband seismic array. Two‐dimensional migration shows the subducting Juan de Fuca crust to at least 80‐km depth, with its surface only 68 ± 2 km deep beneath MSH. Migration and three‐dimensional stacking reveal a clear upper‐plate Moho east of MSH that disappears west of it. This disappearance is a result of both hydration of the mantle wedge and a westward change in overlying crust. Migration images also show that the subducting plate continues without break along strike. Combined with low temperatures inferred for the mantle wedge, this geometry greatly limits possible source regions for mantle melts that contribute to MSH magmas and requires lateral migration over large distances.

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“…The melt transport pathway is not understood, since heat flow within a few kilometers of the MSH edifice is markedly low compared to the arc and backarc (Blackwell et al, ; van Keken et al, ). Furthermore, erupted dacites record equilibration temperatures of 925–940 °C at lower crustal pressures of 700–900 MPa (Blatter et al, ), but such high temperatures seem inconsistent with low heat flow and the inferred presence of serpentinized mantle. Nearby basaltic vents require even hotter mantle temperatures (Leeman et al, ).…”

Section: Introductionmentioning

confidence: 99%

Shear Velocity Structure From Ambient Noise and Teleseismic Surface Wave Tomography in the Cascades Around Mount St. Helens

et al. 2019

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Mount St. Helens (MSH) lies in the forearc of the Cascades where conditions should be too cold for volcanism. To better understand thermal conditions and magma pathways beneath MSH, data from a dense broadband array are used to produce high‐resolution tomographic images of the crust and upper mantle. Rayleigh‐wave phase‐velocity maps and three‐dimensional images of shear velocity (Vs), generated from ambient noise and earthquake surface waves, show that west of MSH the middle‐lower crust is anomalously fast (3.95 ± 0.1 km/s), overlying an anomalously slow uppermost mantle (4.0–4.2 km/s). This combination renders the forearc Moho weak to invisible, with crustal velocity variations being a primary cause; fast crust is necessary to explain the absent Moho. Comparison with predicted rock velocities indicates that the fast crust likely consists of gabbros and basalts of the Siletzia terrane, an accreted oceanic plateau. East of MSH where magmatism is abundant, middle‐lower crust Vs is low (3.45–3.6 km/s), consistent with hot and potentially partly molten crust of more intermediate to felsic composition. This crust overlies mantle with more typical wave speeds, producing a strong Moho. The sharp boundary in crust and mantle Vs within a few kilometers of the MSH edifice correlates with a sharp boundary from low heat flow in the forearc to high arc heat flow and demonstrates that the crustal terrane boundary here couples with thermal structure to focus lateral melt transport from the lower crust westward to arc volcanoes.

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Voluminous arc dacites as amphibole reaction-boundary liquids

Cited by 76 publications

References 87 publications

A mineral and cumulate perspective to magma differentiation at Nisyros volcano, Aegean arc

A mineral and cumulate perspective to magma differentiation at Nisyros volcano, Aegean arc

Imaging Subduction Beneath Mount St. Helens: Implications for Slab Dehydration and Magma Transport

Shear Velocity Structure From Ambient Noise and Teleseismic Surface Wave Tomography in the Cascades Around Mount St. Helens

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