Other
Scientific paper
Jun 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002e%26psl.200..131l&link_type=abstract
Earth and Planetary Science Letters, Volume 200, Issue 1-2, p. 131-146.
Other
9
Scientific paper
Mesoscale pervasive magma migration leads to granite injection complexes, common in hot crustal terranes. Pervasive migration is limited by magma freezing when intruding cold country rock. Here, we explore numerically the feedback mechanism between magma intrusion and heating of the country rock, which allows younger intrusive batches to reach increasingly shallower/cooler levels. This process relies on the higher solidus temperature of a rock compared to that of its melt, once melt is segregated. We define the `free-ride layer' as the region above the melt source, where magma may freely migrate because rock temperature is above melt solidus. The top of the free-ride layer, which corresponds to the melt solidus (TS) isotherm, is at the `limiting depth', zS. After magma passes through the free-ride layer, the magma `front' is always at the limiting depth. We modeled the thickening and heating of the crust above the source as melt at its liquidus (TL) intrudes it pervasively from below. We found that: (a) magma quickly warms crust below zS to about TL, forming a step in temperature at zS; (b) the front (zS) moves up through the crust as more magma is intruded; (c) as magma is emplaced at the front, a mingled layer of about half magma half crust forms below it, so that the total rise of the front corresponds approximately to half of the thickness of magma added to the free-ride layer; (d) the rate of rise of the front depends on the temperature difference between crust and TL, and slows down as the magma front rises; (e) for most reasonable intrusion rates and volumes, the crust above zS feels little influence of the intrusion, because the diffusion time scale is much smaller than the rise rate of the front. In summary, pervasive migration is an efficient way of heating the lower to middle crust, and can result in an injection complex several kilometers thick, consisting of about half magma and half original crust.
Leitch Alison M.
Weinberg Roberto F.
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