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Magmatic Intrusions (magmatic + intrusion)
Selected AbstractsViscoelastic displacement and gravity changes due to point magmatic intrusions in a gravitational layered solid earthGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2001José Fernández Summary We present a method for the computation of time-dependent geodetic and geophysical signatures (deformation, potential and gravity changes) due to magmatic intrusions in a layered viscoelastic,gravitational medium. This work is an extension of a deformation model previously developed to compute effects due to volcanic loading in an elastic gravitational layered media. The model assumes a planar earth geometry, useful for near field problems, and consists of welded elastic and viscoelastic layers overlying a viscoelastic half-space. Every layer can either be considered elastic or viscoelastic. The intrusion (treated as a point source) can be located at any depth, in any of the layers or in the half-space. Several examples of theoretical computations for different media are also presented. We have found that, in line with previous results obtained by other authors, introducing viscoelastic properties in all or part of the medium can extend the effects (displacements, gravity changes, etc.) considerably and therefore lower pressure increases are required to model given observed effects. The viscoelastic effects seem to depend mainly on the rheological properties of the layer (zone) where the intrusion is located, rather than on the rheology of the whole medium. We apply our model to the 1982,1984 uplift episode at Campi Flegrei, modelling simultaneously the observed vertical displacement and gravity changes. The results clearly show that for a correct interpretation of observed effects it is necessary to include the gravitational field in the anelastic theoretical models. This factor can change the value and pattern of time-dependent deformation as well as the gravity changes, explaining cases of displacement without noticeable gravity changes or vice versa, cases with uplift and incremental gravity values, and other cases. The combination of displacement and gravity changes is found to be especially effective in constraining the possible characteristics of the magmatic intrusion as well as the rheology of the medium surrounding it. [source] Synchronous peak Barrovian metamorphism driven by syn-orogenic magmatism and fluid flow in southern Connecticut, USAJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2008P. J. LANCASTER Abstract Recent work in Barrovian metamorphic terranes has found that rocks experience peak metamorphic temperatures across several grades at similar times. This result is inconsistent with most geodynamic models of crustal over-thickening and conductive heating, wherein rocks which reach different metamorphic grades generally reach peak temperatures at different times. Instead, the presence of additional sources of heat and/or focusing mechanisms for heat transport, such as magmatic intrusions and/or advection by metamorphic fluids, may have contributed to the contemporaneous development of several different metamorphic zones. Here, we test the hypothesis of temporally focussed heating for the Wepawaug Schist, a Barrovian terrane in Connecticut, USA, using Sm,Nd ages of prograde garnet growth and U,Pb zircon crystallization ages of associated igneous rocks. Peak temperature in the biotite,garnet zone was dated (via Sm,Nd on garnet) at 378.9 ± 1.6 Ma (2,), whereas peak temperature in the highest grade staurolite,kyanite zone was dated (via Sm,Nd on garnet rims) at 379.9 ± 6.8 Ma (2,). These garnet ages suggest that peak metamorphism was pene-contemporaneous (within error) across these metamorphic grades. Ion microprobe U,Pb ages for zircon from igneous rocks hosted by the metapelites also indicate a period of syn-metamorphic peak igneous activity at 380.6 ± 4.7 Ma (2,), indistinguishable from the peak ages recorded by garnet. A 388.6 ± 2.1 Ma (2,) garnet core age from the staurolite,kyanite zone indicates an earlier episode of growth (coincident with ages from texturally early zircon and a previously published monazite age) along the prograde regional metamorphic T,t path. The timing of peak metamorphism and igneous activity, as well as the occurrence of extensive syn-metamorphic quartz vein systems and pegmatites, best supports the hypothesis that advective heating driven by magmas and fluids focussed major mineral growth into two distinct episodes: the first at c. 389 Ma, and the second, corresponding to the regionally synchronous peak metamorphism, at c. 380 Ma. [source] | ||||||||||