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Figure 7.20. The shaded region denotes a large granite body, which intruded at
700 C: (a) 1 Ma, (b) 2 Ma and (c) 5 Ma after intrusion, the granite is cooling and
solidifying and heating the country rock; (d) 20 Ma after intrusion, the high heat
generation of the granite means that temperatures in and around it are elevated.
(From Fowler and Nisbet (1982).)
important cause of regional metamorphism. Beneath and around the intrusion
at depth, temperatures may be raised to such an extent that some local partial
melting takes place in the country rock, which may cause further intrusion. If this
occurs, then low 87 Sr
86 Sr initial ratios will be measured at the top of the original
intrusion; younger, high 87 Sr
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86 Sr initial ratios and young partial-melting textures
will be present at the base of the pluton and below. Unravelling the history of the
intrusion would be very difficult.
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