Thermodynamic modeling of high-grade metabasites: a case study using the Tso Morari UHP eclogite
Thermodynamic modeling of high-grade metabasites: a case study using the Tso Morari UHP eclogite
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DOI：
10.1007/s00410-020-01717-w
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发表时间：
2020-07
影响因子：
3.5
通讯作者：
Ruiguang Pan;C. Macris;Carrie A. Menold
中科院分区：
文献类型：
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作者：
Ruiguang Pan;C. Macris;Carrie A. Menold
热动力学模拟是研究变质岩演化，特别是研究保存较差的变质反应的重要手段。新的热力学建模技术的发展和更新的热力学数据库和活性-组成（a-X）关系的可用性，要求评估的最佳做法，模拟压力-温度（P-T）路径的变碱岩。在本文中，榴辉岩从Tso Morari超高压火山口，西北印度，被用来作为一个代表性的变质基性岩直接比较的输出（伪截面和P-Tpaths）产生的广泛使用的THERMOCALC和Theriak-Domino程序的最新版本。我们还评估了使用最新热力学数据库（ds 62，Holland和Powell in J Metamorph Geol 29（3）：333-383，10.1111/j.1525-1314.2010.00923.x，2011）相对于较旧版本（ds 55，Holland和Powell in J Metamorph Geol 16（3）：309-343，10.1111/j.1525-1314.1998.00140.x，1998）的影响，以及用户选择矿物-X关系的影响，同时考虑石榴石分馏对岩石有效体积成分的影响。（1）TC 33; THERMOCALC 3.33版本，数据库ds 55和白色等人的garneta-X关系。（J Metamorph Geol 25（5）：511-527，10.1111/j.1525-1314.2007.00711.x，2007）;（2）TC 47; THERMOCALC版本3.47，具有数据库ds 62和白色等人的石榴石-X关系。（J Metamorph Geol 32（3）：261-286，10.1111/jmg.12071，2014 a）;（3）TDG; Theriak-Domino，具有白色等人的数据库ds 62和garneta-Xrelations（2014 a），以及（4）TDW; Theriak-Domino，具有白色等人的数据库ds 62和garneta-Xrelations（2007）。TC 47和TDG模型分别在544 ± 15 °C和551 ± 12 °C下产生类似的峰值变质P-T，为34 ± 1.5 kbar。结果在压力上比从TC 33建模（在565 ± 8 °C下26 ± 1 kbar）和TDW建模（在563 ± 13 °C下28.5 ± 1.5 kbar）确定的压力高5-8 kbar。结果表明，所有四个建模协议一般提供一致的变质相关系和热力学模拟分馏的散装组合物和变质的不确定性。在所有模型计算中，由XRF测量的初始体成分并不代表石榴石成核时的有效体成分。石榴石-X关系的选择可以影响峰值压力的预测，无论程序选择。这项研究说明了仔细考虑选择哪种X关系的重要性，以及需要将建模预测与岩石本身的地球化学和岩相学证据进行比较。
Thermodynamic modeling is an important technique to simulate the evolution of metamorphic rocks, particularly the poorly preserved prograde metamorphic reactions. The development of new thermodynamic modeling techniques and availability of updated thermodynamic databases and activity–composition (a–X) relations, call for an evaluation of best practices for modeling pressure–temperature (P–T) paths of metabasites. In this paper, eclogite from the Tso Morari UHP terrane, NW India, is used as a representative metabasite to directly compare the outputs (pseudosections andP–Tpaths) generated from recent versions of the widely used THERMOCALC and Theriak-Domino programs. We also evaluate the impact of using the most updated thermodynamic database (ds 62, Holland and Powell in J Metamorph Geol 29(3):333–383, 10.1111/j.1525-1314.2010.00923.x, 2011) relative to an older version (ds 55, Holland and Powell in J Metamorph Geol 16(3):309–343, 10.1111/j.1525-1314.1998.00140.x, 1998), and the effect of the user’s choice of minerala–Xrelations while considering the effect of garnet fractionation on the rock’s effective bulk composition. The following modeling protocols were assessed: (1) TC33; THERMOCALC version 3.33 with database ds 55 and garneta–Xrelations of White et al. (J Metamorph Geol 25(5):511–527, 10.1111/j.1525-1314.2007.00711.x, 2007); (2) TC47; THERMOCALC version 3.47 with database ds 62 and garneta–Xrelations of White et al. (J Metamorph Geol 32(3):261–286, 10.1111/jmg.12071, 2014a); (3) TDG; Theriak-Domino with database ds 62 and garneta–Xrelations of White et al. (2014a), and (4) TDW; Theriak-Domino with database ds 62 and garneta–Xrelations of White et al. (2007). TC47 and TDG modeling yield a similar peak metamorphicP–Tof 34 ± 1.5 kbar at 544 ± 15 °C and 551 ± 12 °C, respectively. The results are 5–8 kbar higher in pressure than that determined from TC33 modeling (26 ± 1 kbar at 565 ± 8 °C), and TDW modeling (28.5 ± 1.5 kbar at 563 ± 13 °C). Results indicate that all four modeling protocols generally provide consistent metamorphic phase relations and thermodynamic simulations regarding fractionation of the bulk composition and prograde metamorphism within uncertainty. In all model calculations, the initial bulk composition measured by XRF does not represent the effective bulk composition at the time of garnet nucleation. The choice of garneta–Xrelations can affect predictions of peak pressure, regardless of program choice. This study illustrates the importance of careful consideration of whicha–Xrelations one chooses, as well as the need for comparison between modeling predictions and evidence from the geochemistry and petrography of the rock(s) themselves.