A felsic MASH zone of crustal magmas — Feedback between granite magma intrusion and in situ crustal anatexis

Lithos ◽  
2017 ◽  
Vol 284-285 ◽  
pp. 109-121 ◽  
Author(s):  
Martin Schwindinger ◽  
Roberto F. Weinberg
Keyword(s):  
Crustal Anatexis ◽  
Magma Intrusion ◽  
Granite Magma

Age constraints for rare felsic mantle xenoliths from Elie Ness, Scottish Midland Valley

2020 ◽  
Author(s):  
Eszter Badenszki ◽  
J. Stephen Daly ◽  
Martin J. Whitehouse ◽  
Brian G. J. Upton
Keyword(s):  
Upper Mantle ◽  
Solid Phase ◽  
Mantle Xenoliths ◽  
Solid Phase Reaction ◽  
Phase Reaction ◽  
Magma Intrusion ◽  
Accessory Zircon ◽  
Complex Source ◽  
Age Constraints

<p>EN-101, a rare albitite [Pl +Fe-Ti oxide +Ap +Zrn] xenolith from Elie Ness, Scottish Midland Valley, is hosted by a c. 290 Ma old alkali basaltic diatreme [1, 2].  EN-101 is considered to belong to the Scottish “anorthoclasite suite” comprising xenoliths and megacrysts of various compositions which are interpreted as samples from the upper mantle – lower crust where they form (syenitic) vein or dyke-like bodies e.g., [3, 4, 5]. The “anorthoclasite suite” has been found in all Scottish terranes suggesting that the presumed dyke system must be extensive.</p><p>Xenoliths of the “anorthoclasite suite” primarily consist of Na-rich and Ca-poor feldspar megacrysts, with generally high Na/K ratios [3] that are typically accompanied by accessory zircon, apatite, biotite, magnetite and Fe-rich pyroxene whereas garnet and corundum with Nb-rich oxides are only occasionally present [3, 4, 5]. Upton et al. [4, 5] argued that the parental melt of the “anorthoclasite suite” formed though small–fraction melting of metasomatized mantle and subsequent melt–solid phase reaction was also involved.  Upton et al. [5] proposed that crystallization of the anorthoclasite suite samples occurred shortly prior to- or contemporaneously with their entrainment. However so far no in-situ dating has been carried out on these samples.</p><p>Early attempts to date the anorthoclasite suite using zircon and feldspar megacrysts from Elie Ness suggested at least a two-stage formation mechanism, where zircon megacrysts yielded a U-Pb age of c. 318 Ma, while euhedral feldspar xenocrysts are significantly younger and roughly coeval with the host volcanism yielding a K-Ar whole-rock age of c. 294 Ma [6].  In this study we present the first in situ U-Pb dating of zircon, which yielded a concordia age of 328 ± 2 Ma (MSWD=0.19; n=12) for EN-101. Zircons εHf<sub>328</sub> values range from +5.2 to +7.5 consistent with a mildly depleted source refreshed by metasomatism. These results may indicate that the proposed extensive syenitic veining within the Scottish upper mantle not only has a complex source [5], but is possibly the result of repeated episodes of magma intrusion.</p><p>References:</p><ol><li>Gernon, T.M. et al. 2013 Bulletin of Volcanology. 75:1-20.</li> <li>Gernon, T.M. et al. 2016 Lithos. 264:70-85.</li> <li>Aspen, P. et al. 1990 European Journal of Mineralogy 2:503-17.</li> <li>Upton, B.G.J. et al. 1990 Journal of Petrology.40:935-56.</li> <li>Upton, B.G.J. et al. 2009 Mineral Mag. 73:943-56.</li> <li>Macintyre, R.M. et al. 1981 Transactions of the Royal Society of Edinburgh: Earth Sciences. 72:1-7.</li> </ol>

Crustal anatexis and its relation to the exhumation of collisional orogenic belts, with particular reference to the Himalaya

2002 ◽  
Vol 66 (1) ◽  
pp. 53-91 ◽  
Author(s):  
A. G. Whittington ◽  
P. J. Treloar
Keyword(s):  
Volume Fraction ◽  
Thermal Conditions ◽  
Western Himalaya ◽  
Crustal Anatexis ◽  
Accessory Phase ◽  
Small Volume Fraction ◽  
Active Processes ◽  
Metamorphic Terranes ◽  
Orogenic Belts

AbstractWe review the causes, mechanisms and consequences of crustal anatexis during the exhumation of metamorphic terranes, from a petrological perspective. During both prograde and retrograde metamorphism, limited influx of free hydrous fluids may result in small volumes of very hydrous melts, which cannot ascend far (if at all) before reaching their solidus. If thermal conditions for dehydration melting are attained in fertile micaceous crustal layers, much larger volumes of water-undersaturated granitic magmas may result, especially where limited external fluid influx raises water activities above those that may be buffered by dehydrating hydrous phases. Magmas have specific trace element characteristics depending on the reaction which formed them which, combined with accessory phase thermometry, may enable the (P-T) conditions of melting to be ascertained. Small volume-fraction magmas will typically remain as in situ migmatites unless their extraction is assisted by deformation. In turn, deformation will be focused in weaker partially molten zones, so that water-undersaturated magmas may often be mobilized. Once segregated, their ascent is limited by the rate of dyke propagation, and they may reach shallow levels (<2 kbar) before crystallizing. The complex interplay between deformation and melting is exemplified by the Miocene evolution of the central Himalaya, where thrust and normal faulting, melting and exhumation were all simultaneously active processes which were linked by feedback relations. In the Nanga Parbat Massif of the western Himalaya, rapid post-Miocene denudation and vigorous fluid flux enabled rocks to experience more than one episode of melting simultaneously, at different levels of the same exhuming crustal section.

Rendez vous with Saturn's rings

1984 ◽  
Vol 75 ◽  
pp. 743-759 ◽  
Author(s):  
Kerry T. Nock
Keyword(s):  
Solar Energy ◽  
Electric Propulsion ◽  
Power Source ◽  
Propulsion System ◽  
Low Thrust ◽  
Ring Plane ◽  
The Earth ◽  
Total Impulse ◽  
Saturn's Rings

ABSTRACTA mission to rendezvous with the rings of Saturn is studied with regard to science rationale and instrumentation and engineering feasibility and design. Future detailedin situexploration of the rings of Saturn will require spacecraft systems with enormous propulsive capability. NASA is currently studying the critical technologies for just such a system, called Nuclear Electric Propulsion (NEP). Electric propulsion is the only technology which can effectively provide the required total impulse for this demanding mission. Furthermore, the power source must be nuclear because the solar energy reaching Saturn is only 1% of that at the Earth. An important aspect of this mission is the ability of the low thrust propulsion system to continuously boost the spacecraft above the ring plane as it spirals in toward Saturn, thus enabling scientific measurements of ring particles from only a few kilometers.

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