Contact-metamorphic zones

In contact-metamorphic zones, in association with magnetite and Fe-rich silicates (feldspathoid-bearing igneous rocks)... 

Hanson G. N. and Gast P. W. (1967). Kinetic studies in contact metamorphic zones. Geochim. Cosmochim. Acta, 31 1119-1153. 

A wollastonite-bearing contact metamorphic zone is observed adjacent to a granite which has intruded a quartz-bearing limestone horizon. Heat-flow calculations indicate that the maximum temperature achieved at a given distance from the contact is given by... 

Figure 11.18 Apparent K-Ar ages of minerals from Idaho Springs Formation (Front Range, Colorado, 1350-1400 Ma) in zone subjected to contact metamorphism by intrusion of a quartz monzonite (Eldora stock, 55 Ma). Reprinted from S. R. Hart, Journal of Geology, (1964), 72, 493-525, copyright 1964 by The University of Chicago, with permission of The University of Chicago Press.

Other Routes. When heat from a magma chamber, or an intrusive dyke, bakes surrounding rocks, zeohtes can be part of the suite of minerals produced in zones via this process of contact metamorphism. This sequence has been identified in the Rhodope Mountains of Bulgaria. Bulgaria also has been cited as the location of proposed geoautoclaves, where enclosed conditions of high temperature and vapor pressure... 

Uranium deposits in this unit are of numerous geological types, but three are typical of the Hercynian orogen (1) intra-granitic deposits related to leucogranites, (2) deposits bound to the contact-metamorphic haloes of granite intrusives in Lower Palaeozoic shales (the so-called Iberian type ) and (3) deposits bound to Permian cover rocks or Permian acid volcanics. Other types are veins in less differentiated granites, veins in metamorphic environments, sandstone-type deposits in Mesozoic or Caenozoic cover rocks in basin structures of the Hercynian space included in or adjacent to the Moldanubian zone (or its Iberian equivalent). 

Ni-Cu-PGE mineralization at Sudbury is zoned with respect to Cu and PGE as a result of fractional crystallization from a base metal sulfide liquid, but metamorphism, fluids and deformation also affected these ore deposits (e.g., Farrow Lightfoot 2002 and authors therein). The two main styles of mineralization are 1) Fe-Ni-rich pyrrhotite ores (with minor pentlandite and chalcopyrite) in embayments along the base of the complex in noritic/gabbronoritic (contact ores) and 2) Cu-Pt-Pd-Au-rich chalcopyrite ores (with minor pentlandite, pyrrhotite and PGM) forming veins and stockworks in the country rock below the complex (footwall ores). Creighton Mine, on the southern margin of the complex, is one of the largest contact-style deposits. 

Barboza S. A. and Bergantz G. W. (2000) Metamorphism and anatexis in the mafic complex contact aureole, Ivrea zone, northern Italy. J. Petrol. 41, 1307-1327. 

Hollister L. S. (1966) Garnet zoning an interpretation based on the Rayleigh fractionation model. Science 154, 1647-1651. Hollister L. S. (1969) Contact metamorhpism in the Kwoiek Area of British Columbia an end member of the metamorphic process. Geol. Soc. Am. Bull. 80, 2465 - 2494. 

The 55 granulite facies samples include 17 that are from near the plutonic contacts of massif-type anorthosite bodies. These samples contain zoned graphite crystals with higher cores that record the pre-regional metamorphism igneous contact... 

Jenkins 2000). No zones of higher temperature were found at exposed igneous contacts, though the locally low values of A C(Cc-Gr) 5 km W of Canton may be an unrecognized contact aureole. The Cc-Gr RAM thermometer provides the best estimates for metamorphic temperature in this terrane. 

The infiltration of surface derived fluids into a contact aureole requires that fluid pressures be close to hydrostatic. Thus, if stable isotope ratios indicate exchange with large amounts of meteoric water, Ph20 must have been much less than Piithostatic at some time during the metamorphic history. The deepest known instances of meteoric water exchange represent the transition towards lithostatic fluid pressure. All known zones of meteoric water infiltration are shallower than 15 km and most are less than 6 km (Valley and O Neil 1982). Likewise, penetration of seawater to depths of 6-7 km in oceanic crust is well documented (Gregory and Taylor 1981). Possibly the deepest known penetration of surface-derived fluids is in veins and in faults of extensional terranes (Fiicke et al. 1992 Nesbitt and Muehlenbachs 1995 Morrison and Anderson 1998). 

The encircling zone of metamorphic rocks around an intrusion is referred to as the contact aureole (Fig. 1.14). The size of an aureole depends on the size and temperature of the intrusion when emplaced, the quantity of hot gases and hydrothermal solutions that emanated from it,... 

If two minerals contact with each other at constant the pressure-temperature condition where two minerals are unstable, reaction occurs between them to form stable mineral. The dominant rate limiting mechanisms are diffusion of aqueous species dissolved from minerals in fluid and dissolution and precipitation reactions. If fluid is not present, diffusion in solid phase occurs. But the rate of diffusion in solid phase is generally very slow. However, at very high temperature and pressure (metamorphic condition) the diffusion in solid phase may control the mass transfer. Reaction-diffusion model is able to be used to obtain the development of reaction zone between two minerals with time. 

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