Dynamic growth of garnet in granitic magmas
Dynamic growth of garnet in granitic magmas
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DOI：
10.1130/g32349.1
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发表时间：
2012-02
期刊：
影响因子：
5.8
通讯作者：
J. Lackey;G. Romero;A. Bouvier;J. Valley
中科院分区：
文献类型：
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作者：
J. Lackey;G. Romero;A. Bouvier;J. Valley
为了加深对副石榴石如何在火成岩中结晶的认识，并评价其作为岩浆历史矿物记录器的价值，我们用激光氟化和离子探针原位分析了美国缅因州中南部哈洛威尔和托格斯两个深成岩体中的石榴石的δ18O。石榴石分为岩浆石榴石和局部包晶石榴石两种类型。一些单晶的横截面显示δ18 O(石榴石)的渐变和突变，通常是~GT；1‰，而其他石榴石颗粒的同位素组成是均匀的。许多晶体中δ-18O的逐渐增加表明，石榴石在生长的同时，高δ-18O变质围岩被同化。包晶颗粒有一个补充记录，即高δ18O熔体转移到深成岩中。在一些岩石中，δ18O在相邻的颗粒之间存在差异，这表明晶体在岩浆混合过程中是间歇性生长的，或者是来自不同来源的并置。石榴石忠实地记录了岩浆δ18O的变化，是解释岩浆成因的有价值的工具。
In order to improve understanding of how accessory garnet crystallizes in igneous rocks, and evaluate it as a mineral recorder of magma history, we analyzed δ 18 O of garnets from the Hallowell and Togus plutons in south-central Maine (United States) by laser fluorination, and in situ by ion microprobe. Two types of garnet are recognized, magmatic and locally derived peritectic. Traverses of some single crystals show both gradual and abrupt changes of δ 18 O(garnet), commonly >1‰, while other garnet grains are isotopically homogeneous. Rimward increase of δ 18 O in many crystals indicates that garnet grew while high δ 18 O metamorphic wall rocks were assimilated. Peritectic grains have a complementary record of the transfer of high δ 18 O melts to the plutons. In some rocks, δ 18 O varies among neighboring grains, evidence that crystals grew episodically or were juxtaposed from different sources during magma mixing. Garnet faithfully records changing magmatic δ 18 O, and is a valuable tool to decipher magma petrogenesis.