Pulsed dehydration and garnet growth during subduction revealed by zoned garnet geochronology and thermodynamic modeling, Sifnos, Greece
Pulsed dehydration and garnet growth during subduction revealed by zoned garnet geochronology and thermodynamic modeling, Sifnos, Greece
复制标题
DOI：
10.1016/j.epsl.2014.12.024
复制
发表时间：
2015-03-01
影响因子：
5.3
通讯作者：
Caddick, Mark J.
中科院分区：
文献类型：
--
作者：
Dragovic, Besim;Baxter, Ethan F.;Caddick, Mark J.
我们使用耦合分区地质年代学和热力学模型的石榴石来阐明的性质和规模的变质脱水始新世俯冲的石英长石岩性从锡弗诺，希腊。两个大的石榴石斑晶进行了微钻样品同心生长带，这些都是用Sm-Nd年代学。为了将结果置于地球动力学背景下，揭示石榴石生长的原因和后果，我们构建了一系列规定的压力-温度（P-T）路径的热力学正演模型。我们的数据揭示了石榴石生长的三个不同阶段：53.4 +/- 2.6 Ma时的初始增长（类似于0.8 GPa和类似于300摄氏度），随后是非常有限的生长期，直到第二阶段，在47.22 +/- 0.36 Ma，然后是主要的生长脉冲，负责最终石榴石体积的大部分，44.96 +/- 0.53 Ma（2.06-2.19 GPa和490-550 ℃）。这表明从晶体核心到边缘的体积生长速率的>2个数量级的加速，最终的生长脉冲快速发生（75 ° C/My.该最终脉冲伴随着类似于0.5重量%的净大块岩石脱水。俯冲通道折返早期阶段的快速加热，或板幔耦合相关的急剧热梯度可能是这种脉冲变质和脱水的原因。因此，石榴石的数据记录了在缓慢而连续的俯冲过程中脱水和加热的集中脉冲。(C)2014爱思唯尔有限公司版权所有。
We use coupled zoned geochronology and thermodynamic modeling of garnet to elucidate the nature and scale of metamorphic dehydration during Eocene subduction of a quartzofeldspathic lithology from Sifnos, Greece. Two large garnet porphyroblasts were microdrilled to sample concentric growth zones, and these were dated using Sm-Nd geochronology. To put results in a geodynamic context and reveal the causes and consequences of garnet growth, we constructed thermodynamic forward models for a series of prescribed pressure-temperature (P-T) paths. Our data reveal three distinct phases of garnet growth: initial growth at 53.4 +/- 2.6 Ma (similar to 0.8 GPa and similar to 300 degrees C), followed by a period of very limited growth until a second phase, at 47.22 +/- 0.36 Ma, and then a major pulse of growth, responsible for the majority of the final garnet volume, at 44.96 +/- 0.53 Ma (2.06-2.19 GPa and 490-550 degrees C). This suggests a >2 order of magnitude acceleration in volumetric growth rate from crystal core to rim, with the final growth pulse occurring rapidly (75 degrees C/My. This final pulse was accompanied by net bulk rock dehydration of similar to 0.5 wt.%. Rapid heating during early stages of exhumation in the subduction channel, or by sharp thermal gradients related to slab-mantle coupling could be causes for this pulsed metamorphism and dehydration. The garnet data thus record a concentrated pulse of dehydration and heating during the otherwise slow and continuous process of subduction. (C) 2014 Elsevier B.V. All rights reserved.