An automated method for the calculation of P–T paths from garnet zoning, with application to metapelitic schist from the Kootenay Arc, British Columbia, Canada
An automated method for the calculation of P–T paths from garnet zoning, with application to metapelitic schist from the Kootenay Arc, British Columbia, Canada
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一种根据石榴石分区计算 P-T 路径的自动方法，适用于加拿大不列颠哥伦比亚省库特尼弧的变泥质片岩
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发表时间：
2013
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影响因子：
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通讯作者：
D. Pattison
中科院分区：
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作者：
D. P. Moynihan;D. Pattison
本文提出了一种基于石榴石分带的P-T轨迹自动计算方法，并用于解释加拿大南部科迪勒拉变质片岩的分带。采用的方法来重建的P-T路径是匹配石榴石组成沿着径向横断面与预测从热力学正演模型，同时迭代地修改的组成，以考虑结晶分离。该方法被应用到一个代表性的样品石榴石和十字石-轴承片岩角闪岩相Barrovian带在加拿大南部的Omineca带。这些片岩中的石榴石分带是同心的，从核部到边缘基本上是连续的。存在三个带，其中前两个与石榴石晶体的扇形带核心相一致。在含有或不含十字石的岩石中，也分别出现了类似的环带，这表明在十字石发育之前，石榴石的生长仅限于十字石P-T路径的初始部分。在大石榴石晶体的生长分区没有显着修改扩散。这种解释是基于石榴石晶体的分区特性，并进一步支持的正演模型的结果，将同时分步结晶和晶内扩散的影响。计算的P-T路径为这种岩石包括一个初始，线性阶段与高dP/dT，和后期阶段为主的加热。本研究中采用的方法可能适用于其他含石榴石的岩石，其中生长分区被保留。
An automated method for the calculation of P–T paths based on garnet zoning is presented and used to interpret zoning in metapelitic schist from the southern Canadian Cordillera. The approach adopted to reconstruct the P–T path is to match garnet compositions along a radial transect with predictions from thermodynamic forward models, while iteratively modifying the composition to account for fractional crystallization. The method is applied to a representative sample of garnet‐ and staurolite‐bearing schist from an amphibolite facies Barrovian belt in the southern Canadian Omineca belt. Garnet zoning in these schists is concentric and largely continuous from core to rim. Three zones are present, the first two of which coincide with sector‐zoned cores of garnet crystals. Similar zoning is developed in rocks that contain or lack staurolite, respectively, suggesting garnet growth was restricted to the initial part of the prograde P–T path prior to the development of staurolite. Growth zoning in large garnet crystals has not been significantly modified by diffusion. This interpretation is based on zoning characteristics of garnet crystals and is further supported by results of a forward model incorporating the effects of simultaneous fractional crystallization and intracrystalline diffusion. The P–T path calculated for this rock includes an initial, linear stage with a high dP/dT, and a later stage dominated by heating. The approach adopted in this study may have application to other garnet‐bearing rocks in which growth zoning is preserved.