Geochemical and Isotopic Evidence for Crustal Assimilation Beneath Krafla, Iceland

Nicholson, Helen; Condomines, Michel; Fitton, J. Godfrey; Fallick, Anthony E.; Grönvold, Karl; Rogers, G.

doi:10.1093/petrology/32.5.1005

Cited by 151 publications

(98 citation statements)

References 24 publications

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“…Though the possibility of plagioclase fractionation may be avoided by using samples only with more than 10wt% MgO, clinopyroxene can appear above this threshold in high-pressure crystallization (Figure 4-5b). However, that clinopyroxene fractionation without plagioclase would result in a large change in CaO/Al 2 0 3 , and such a signal at MgO higher than 10wt% has not been found in our study area [e.g., Meyer et al, 1985;Nicholson et al, 1991;Fram and Lesher, 1997;Thy et al, 1998]. Therefore, we regard the high-pressure liquid line of descent with early clinopyroxene fractionation (e.g., Figure 4-5b, liquid C) as a rather rare case, and will not consider its possibility hereafter.…”

Section: Behavior Of Ni In Crustal Modification Processesmentioning

confidence: 54%

Magmatism and dynamics of continental breakup in the presence of a mantle plume

Korenaga¹

2000

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This thesis studies the dynamics of mantle melting during continental breakups by geophysical, geochemical, and numerical analyses. The first part focuses on the mantle melting and crustal accretion processes during the formation of the Southeast Greenland margin, on the basis of deep-crustal seismic data. A new seismic tomographic method is developed to jointly invert refraction and reflection travel times for a compressional velocity structure, and a long-wavelength structure with strong lateral heterogeneity is successfully recovered, including 30-to 15-km-thick igneous crust within a 150-km-wide continent-ocean transition zone. A nonlinear Monte Carlo analysis is also conducted to establish the absolute uncertainty of model parameters. The derived crustal structure is first used to resolve the origin of a margin gravity high, with new inversion schemes using both seismic and gravity constraints. Density anomalies producing the gravity high seem to be confined within the upper crust, not in the lower crust as suggested for other volcanic margins. A new robust framework is then developed for the petrological interpretation of the velocity structure of igneous crust, and the thick igneous crust formed at the continentocean transition zone is suggested to have resulted from vigorous active upwelling of mantle with only somewhat elevated potential temperature. In the second part, the nature of mantle melting during the formation of the North Atlantic igneous province is studied on the basis of the major element chemistry of erupted lavas. A new fractionation correction scheme based on the Ni concentrations of mantle olivine is used to estimate primary melt compositions, which suggest that this province is characterized by a large degree of major element source heterogeneity. In the third part, the nature of preexisting sublithospheric convection is investigated by a series of finite element analyses, because the strength of such convection is important to define the "normal" state of mantle, the understanding of which is essential to identify any anomalous behavior of mantle such as a mantle plume. The results suggest that small-scale convection is likely in normal asthenosphere, and that the upwelling velocity in such convection is on the order of 1-10 cm/yr. 271 Introductory NotesThis thesis is composed of three parts, all of which are related to the dynamics of mantle melting during continental breakups. In the first part, rifting magmatism associated with the opening of the North Atlantic (at -60 Ma) is investigated on the basis of deep-crustal seismic data collected across the Southeast Greenland continental margin. A new seismic tomographic method is developed to jointly invert refraction and reflection travel times for a two-dimensional velocity structure (Chapter 1). Several key issues in travel time tomography such as velocity-depth ambiguity and absolute parameter uncertainty are identified, and a practical strategy is presented to resolve them. The derived crustal velocity structure is the...

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Section: Behavior Of Ni In Crustal Modification Processesmentioning

confidence: 54%

Magmatism and dynamics of continental breakup in the presence of a mantle plume

Korenaga¹

2000

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“…The remaining trace elements and rare earth elements (REE) appear to have escaped extensive alteration, and normalized diagrams indicate the Zebulon rhyolites are comparable to high-temperature rhyolites derived from partial melts from a basaltic source ( Fig. 9; e.g., Nicholson et al 1991;Cousens 1996). These Zebulon Formation felsic rocks are similar to high-silica rhyolites from suprasubduction zone environments, such as the Taupo volcanic zone in New Zealand, the Long Valley caldera of the western USA (Fig.…”

Section: Stratigraphy and Petrological Evolutionmentioning

confidence: 91%

Chronostratigraphy of the Hottah terrane and Great Bear magmatic zone of Wopmay Orogen, Canada, and exploration of a terrane translation model

et al. 2015

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Abstract:The Paleoproterozoic Hottah terrane is the westernmost exposed bedrock of the Canadian Shield and a critical component for understanding the evolution of the Wopmay Orogen. Thirteen new high-precision U-Pb zircon crystallization ages are presented and support field observations of a volcano-plutonic continuum from Hottah terrane through to the end of the Great Bear magmatism, from >1950 to 1850 Ma. The new crystallization ages, new geochemical data, and newly published detrital zircon U-Pb data are used to challenge hitherto accepted models for the evolution of the Hottah terrane as an exotic arc and microcontinent that arrived over a west-dipping subduction zone and collided with the Slave craton at ca. 1.88 Ga. Although the Hottah terrane does have a tectonic history that is distinct from that of the neighbouring Slave craton, it shares a temporal history with a number of domains to the south and east -domains that were tied to the Slave craton by ca. 1.97 Ga. It is interpreted herein that Hottah terrane began to the south of its current position and evolved in an active margin over an always east-dipping subduction system that began prior to ca. 2.0 Ga and continued to ca. 1.85 Ga, and underwent tectonic switching and migration. The stratigraphy of the ca. 1913-1900 Ma Hottah plutonic complex and Bell Island Bay Group includes a subaerial rifting arc sequence, followed by basinal opening represented by marginal marine quartz arenite and overlying ca. 1893 Ma pillowed basalt flows and lesser rhyodacites. We interpret this stratigraphy to record Hottah terrane rifting off its parental arc crust -in essence the birth of the new Hottah terrane. This model is similar to rapidly rifting arcs in active margins -for example, modern Baja California. These rifts generally occur at the transition between subduction zones (e.g., Cocos-Rivera plates) and transtensional shear zones (e.g., San Andreas fault), and we suggest that extension-driven transtensional shearing, or, more simply, terrane translation, was responsible for the evolution of Bell Island Bay Group stratigraphy and that it transported this newly born Hottah terrane laterally (northward in modern coordinates), arriving adjacent to the Slave craton at ca. 1.88 Ga. Renewed east-dipping subduction led to the Great Bear arc flare-up at ca. 1876 Ma, continuing to ca. 1869 Ma. This was followed by voluminous Great Bear plutonism until ca. 1855 Ma. The model implies that it was the westerly Nahanni terrane and its subducting oceanic crust that collided with this active margin, shutting down the >120 million year old, east-dipping subduction system.

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“…The major and trace element compositions of more evolved (and more abundant) quartz-tholeiites like the samples from Draugarhraun (which are characterized by low CaO and Al 2 O 3 , negative Sr and Eu anomalies; Table 1, Figures 2 and 3) indicate that combined olivineplagioclase-clinopyroxene (ol-plag-cpx) fractionation must be important [Nicholson et al, 1991;Maclennan et al, 2001] as is typical for MORB in general [Albarède, 1992]. The Draugarhraun basalts and other Icelandic quartz-tholeiites, however, do not lie on a common liquid line of descent with the high-MgO Theistareykir basalts (> 8 wt% MgO; Figure 2).…”

Section: Appendix a A1 Fractionation Processes In High Mgo Suites Comentioning

confidence: 96%

“…Reykjanes Peninsula: Zindler et al [1979], Elliott et al [1991], Hemond et al [1993], Salters and White [1998], Condomines et al [1983], Sun and Jahn [1975], Dupré and Allègre [1980], Gee et al [1998aGee et al [ , 1998b. Northeastern volcanic zone (NEVZ) : Hemond et al [1988: Hemond et al [ , 1993, Condomines et al [1981Condomines et al [ , 1983, Nicholson et al [1991]. Central Iceland: Hemond et al [1988Hemond et al [ , 1993, Condomines et al [1981Condomines et al [ , 1983, Sun and Jahn [1975].…”

Section: Geochemistry Geophysicsmentioning

confidence: 99%

Theistareykir revisited

Stracke

Zindler

Salters

et al. 2003

Geochem Geophys Geosyst

158

189

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[1] Postglacial basalts from Theistareykir (younger than 10,000 years), northern Iceland, define the depleted end of the spectrum of chemical and isotopic compositions observed in Icelandic volcanics but extend to some of the most enriched chemical and isotopic compositions found in Icelandic tholeiites. A spectacular feature of these basalts is the impressive correlations observed between radiogenic isotope ratios (Sr, Nd, Hf, and Pb) and almost the entire spectrum of major and trace element concentrations and ratios. The radiogenic isotope and major and trace element compositions are little affected by crystal fractionation and are essentially unaffected by interaction with the preexisting crust. The Theistareykir basalts must therefore be relatively close in composition to primary melts from the mantle. Consequently, their chemical and isotopic compositions provide a unique opportunity to investigate the nature of melting beneath Iceland and the geochemical character and origin of the mantle source. Large variations in incompatible element abundances require source heterogeneity, as well as variable extents of melting, to be important factors in determining the final chemical composition of the melts. Melting integrates over a large pressure range and is dominated by melting a depleted peridotite similar to the ambient depleted North Atlantic mantle. The isotopically enriched component is of relatively minor abundance and probably has a lower solidus temperature compared to the depleted component. More than one isotopically enriched component must be involved, but it is difficult to identify the end-member compositions using those of the lavas because of preeruptive averaging and damping of the enriched isotopic signals by mixing with the ambient depleted mantle or melts thereof, suggesting that the isotopic signals in Icelandic melts represent a somewhat muted isotopic signal of the enriched component(s) in the Icelandic source mantle. Comparison of the isotopic arrays of Icelandic basalts with those of global OIB suggests that the dominant enriched

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Geochemical and Isotopic Evidence for Crustal Assimilation Beneath Krafla, Iceland

Cited by 151 publications

References 24 publications

Magmatism and dynamics of continental breakup in the presence of a mantle plume

Magmatism and dynamics of continental breakup in the presence of a mantle plume

Chronostratigraphy of the Hottah terrane and Great Bear magmatic zone of Wopmay Orogen, Canada, and exploration of a terrane translation model

Theistareykir revisited

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