Thermal model for origin of granitic batholiths

Hodge, Dennis S.

doi:10.1038/251297a0

Cited by 46 publications

(17 citation statements)

References 8 publications

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“…As oceanic subduction continued, slab rollback occurred. In this case, heat from the underplating of basaltic magma is capable of reaching higher levels in the crust (e.g., Chappell & White, ; Collins & Vernon, ; Ducea & Barton, ; Hodge, ; Huppert & Sparks, ), causing an enhanced melting of the juvenile lower crust that has been thinned during the normal subduction (Figure a) accompanied with the anatexis of the AMUC (Figure b; e.g., Barbarin, ; Kay & Coira, ; Tepper et al, ). Such a process can incorporate abundant enriched AMUC melts into the magmatic systems during magma ascent and cause intense magmatic flare‐up (Figure b), which explains the generation of widespread high‐K calc‐alkaline granitoids as represented by the Group II samples.…”

Section: Discussionmentioning

confidence: 99%

Transition From Low‐K to High‐K Calc‐Alkaline Magmatism at Approximately 84 Ma in the Eastern Pontides (NE Turkey): Magmatic Response to Slab Rollback of the Black Sea

et al. 2018

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Compositional changes of magma in space and time can be used to infer mantle dynamics and crust‐mantle interaction that are responsible for the generation of magma and evolution. This study reveals, for the first time, the presence of magma compositional transition at approximately 84 Ma in the eastern Pontides arc (NE Turkey), providing important insights into the mantle dynamics responsible for the generation of the extensive Late Cretaceous arc magmatism. The Late Cretaceous granitoids can be divided geochemically into two groups. Group I samples were emplaced at 91–86 Ma and are characterized by low K2O/Na2O, whereas Group II samples were emplaced at 83–78 Ma and display high K2O/Na2O. Group I samples have positive zircon εHf (t), whole‐rock ɛNd (t), and mantle‐like zircon δ18O, which significantly differs from the Group II samples with negative to positive εHf (t), negative whole‐rock ɛNd (t), and enhanced zircon δ18O. The Nd‐Hf‐O isotopic compositions of the Group I and II samples can be quantitatively interpreted as being derived from partial melting of the low‐K amphibolite source within the juvenile lower arc crust that incorporated 5–30% and 50–60% enriched components from the basement rocks into the magmatic systems, respectively. Considering the occurrences of regional thermal subsidence and extensional structure during the Late Cretaceous, the compositional transition from Group I to II and the coeval magmatic flare‐up represented by Group II samples can be linked with the slab rollback of the southward subducting Black Sea (Paleotethys) oceanic lithosphere.

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Section: Discussionmentioning

confidence: 99%

Transition From Low‐K to High‐K Calc‐Alkaline Magmatism at Approximately 84 Ma in the Eastern Pontides (NE Turkey): Magmatic Response to Slab Rollback of the Black Sea

et al. 2018

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“…First, the model must include the addition of hot magma or heat, to initially solid crust, in order to create and grow the reservoir. 22,23,[31][32][33][34] Second, the model must include the relative motion of melt and crystals, to allow chemical differentiation. 10,[34][35][36][37] Third, the model must operate primarily at low melt fraction, consistent with a wealth of evidence that crustal magma reservoirs are normally low melt fraction mushes rather than high melt fraction magma chambers.…”

Section: Model Formulationmentioning

confidence: 99%

Chemical differentiation, cold storage and remobilization of magma in the Earth’s crust

Jackson

Blundy

Sparks

2018

Nature

263

229

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The formation, storage and chemical differentiation of magma in the Earth's crust is of fundamental importance in igneous geology and volcanology. Recent data are challenging the high melt fraction 'magma chamber' paradigm that has underpinned models of crustal magmatism for over a century, suggesting instead that magma is normally stored in low melt fraction 'mush reservoirs'. 1-9 A mush reservoir comprises a porous and permeable framework of closely packed crystals with melt present in the pore space. 1,10 However, many common features of crustal magmatism have not yet been explained by either the 'chamber' or 'mush' reservoir concepts. 1,11 Here we show that reactive melt flow is a critical, but hitherto neglected, process in crustal mush reservoirs, occurring because buoyant melt percolates upwards through, and reacts with, the crystals. 10 Reactive melt flow in mush reservoirs produces the low crystallinity, chemically differentiated (silicic) magmas which ascend to form shallower intrusions or erupt to the surface. 11-13 The magmas can host much older crystals, stored at low and even sub-solidus temperatures, consistent with crystal chemistry data. 6-9 Changes in local bulk composition caused by reactive melt flow, rather than significant increases in temperature, produce the rapid increase in melt fraction that remobilizes these cool-or cold-stored crystals. Reactive flow can also produce bimodality in magma compositions sourced from mid-to lower-crustal reservoirs. 14,15 Trace element profiles generated by reactive flow are similar to those observed in a well-studied reservoir now exposed at the surface. 16 We propose that magma storage and differentiation primarily occurs by reactive melt flow in long-lived mush reservoirs, rather than by the commonly invoked process of fractional crystallisation in magma chambers. 14 Magma reservoirs occur at several depths within the crust and typically grow incrementally through the intrusion of dykes or sills. 1,11,13,16,17 High melt fractions must sometimes be present in these reservoirs to produce eruptible, low-crystallinity magmas. 1,7,8,9,13 However, geophysical data suggest that reservoirs have low melt fraction even beneath active volcanoes 2-5 and crystal chemistry data indicate that long-term magma storage occurs at low or even sub-solidus temperature. 6-9 High melt fractions are therefore ephemeral, yet geochemical models typically assume differentiation occurs by crystal fractionation from low-crystallinity magmas; 11,14 moreover, geochronological data demonstrate that crustal magma reservoirs can be long-lived, spanning hundreds of thousands to millions of years. 17-21 Existing models of crustal magma storage and differentiation cannot reconcile these conflicting observations. We use numerical modelling to investigate the storage and chemical differentiation of magma in crustal reservoirs. The model describes repeated intrusion of mafic to intermediate sills into the mid-to lower crust, 12,13,16,21-23 the associated transport of heat via conduction and ad...

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“…This shell promotes a region of stress relaxation in the crust immediately adjacent to the magma reservoir, which effectively acts as a filter, modifying the stress transfer between the walls of the magma chamber, and the surrounding crust. Field evidence and thermal models demonstrate that thermal aureoles may develop in the host rock surrounding magma intrusions [ Hodge , ; Gasparini et al ., ]. There is strong evidence for the existence of a thermal or metamorphic aureole beneath the Kameni islands, both from basement rock inclusions in Kameni lavas [ Nicholls , ] and from the carbon‐isotopic compositions of Kameni CO 2 emissions [e.g., Parks et al ., ; Tassi et al ., ].…”

Section: Modeling and Interpretationmentioning

confidence: 99%

From quiescence to unrest: 20 years of satellite geodetic measurements at Santorini volcano, Greece

et al. 2015

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Periods of unrest at caldera-forming volcanic systems characterized by increased rates of seismicity and deformation are well documented. Some can be linked to eventual eruptive activity, while others are followed by a return to quiescence. Here we use a 20 year record of interferometric synthetic aperture radar (InSAR) and GPS measurements from Santorini volcano to further our understanding of geodetic signals at a caldera-forming volcano during the periods of both quiescence and unrest, with measurements spanning a phase of quiescence and slow subsidence (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), followed by a phase of unrest (January 2011 to April 2012) with caldera-wide inflation and seismicity. Mean InSAR velocity maps from 1993-2010 indicate an average subsidence rate of~6 mm/yr over the southern half of the intracaldera island Nea Kameni. This subsidence can be accounted for by a combination of thermal contraction of the 1866-1870 lava flows and load-induced relaxation of the substrate. For the period of unrest, we use a joint inversion technique to convert InSAR measurements from three separate satellite tracks and GPS observations from 10 continuous sites into a time series of subsurface volume change. The optimal location of the inflating source is consistent with previous studies, situated north of Nea Kameni at a depth of~4 km. However, the time series reveals two distinct pressure pulses. The first pulse corresponds to a volume change (ΔV) within the shallow magma chamber of (11.56 ± 0.14) × 10 6 m 3 , and the second pulse has a ΔV of (9.73 ± 0.10) × 10 6 m 3 . The relationship between the timing of these pulses and microseismicity observations suggests that these pulses may be driven by two separate batches of magma supplied to a shallow reservoir. We find no evidence suggesting a change in source location between the two pulses. The decline in the rates of volume change at the end of both pulses and the observed lag of the deformation signal behind cumulative seismicity, suggest a viscoelastic response. We use a simple model to show that two separate pulses of magma intruding into a shallow magma chamber surrounded by a viscoelastic shell can account for the observed temporal variation in cumulative volume change and seismicity throughout the period of unrest. Given the similarities between the geodetic signals observed here and at other systems, this viscoelastic model has potential use for understanding behavior at other caldera systems.

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Thermal model for origin of granitic batholiths

Cited by 46 publications

References 8 publications

Transition From Low‐K to High‐K Calc‐Alkaline Magmatism at Approximately 84 Ma in the Eastern Pontides (NE Turkey): Magmatic Response to Slab Rollback of the Black Sea

Transition From Low‐K to High‐K Calc‐Alkaline Magmatism at Approximately 84 Ma in the Eastern Pontides (NE Turkey): Magmatic Response to Slab Rollback of the Black Sea

Chemical differentiation, cold storage and remobilization of magma in the Earth’s crust

From quiescence to unrest: 20 years of satellite geodetic measurements at Santorini volcano, Greece

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