Supercooled melt inclusions in lower-crustal granulites as a consequence of rapid exhumation by channel flow

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• 作者：Yoshikuni Hiroi ; Ayahiko Yanagi ; Mutsumi Kato ; Tomoyuki Kobayashi ; Bernard Prame ; Tomokazu Hokada ; Madhusoodhan Satish-Kumar ; Masahiro Ishikawa ; Tatsuro Adachi ; Yasuhito Osanai ; Yoichi Motoyoshi ; Kazuyuki Shiraishi
• 关键词：Felsite inclusions ; Granulite exhumation ; Supercooling ; Spherulite ; Dendrite
• 刊名：Gondwana Research
• 出版年：January, 2014
• 年：2014
• 卷：25
• 期：1
• 页码：226-234
• 全文大小：4846 K

文摘

Here we report on the unexpected occurrence of felsic (granitic) inclusions with quench textures such as spherulite and dendrite (hereafter referred to as 鈥渇elsite inclusions鈥?, similar to some volcanic rocks, within garnet in presumably 鈥渟lowly cooled鈥?lower-crustal granulites of various geologic ages ranging from Early Proterozoic to Middle Paleozoic and wide global distribution (the Limpopo Belt, the Grenville Province, the L眉tzow-Holm Complex of East Antarctica, the Highland Complex of Sri Lanka, and the southern Bohemian Massif). The well-preserved textures of felsite inclusions are indicative of melts formed by anatexis during high-pressure and high-temperature metamorphism, crystallization under far-from-equilibrium conditions (at > 50 掳C undercooling) and subsequent rapid cooling. The occurrence of felsite inclusions in granulites in restricted tectonostratigraphic zones in Sri Lanka, among other examples, may be the first geologic evidence for fast exhumation of lower-crustal rocks to andalusite-stable upper-crustal conditions by channel flow in a continental collision orogen. We hypothesize that granulites ascend episodically along discrete high-strain zones and cool as fast as some felsic magmas. This conclusion sheds new light on the debate regarding the deep crustal processes and necessitates changes to fundamental beliefs about exhumation rates based on rates of plate convergence (1-10 cm/year).