Mass transfer associated with chloritization in the hydrothermal alteration process of granitic pluton
Mass transfer associated with chloritization in the hydrothermal alteration process of granitic pluton
复制标题
DOI：
10.2138/am-2021-7353
复制
发表时间：
2020-11
影响因子：
3.1
通讯作者：
T. Yuguchi;T. Matsuki;Y. Izumino;E. Sasao;T. Nishiyama
中科院分区：
文献类型：
--
作者：
T. Yuguchi;T. Matsuki;Y. Izumino;E. Sasao;T. Nishiyama
摘要本研究沿着我们以前的研究（Yuguchi et al. 2015，2019 a），揭示了岩体中的热液蚀变过程，重点是矿物和热液流体之间的质量转移。它还描绘了流体化学的顺序变化，作为蚀变的进展。本研究的研究区域-日本远野Toki花岗岩的热液蚀变经历了绿泥石化、斜长石蚀变和碳酸盐沉淀的连续过程。本文从岩石学和矿物化学角度论述了角砾绿泥石化、钾长石绿泥石化的蚀变过程及充填型角砾的形成。一组奇异值分解分析进行，以获得绿泥石化过程的反应方程，这有利于定量评估的反应物和产物矿物之间的传质，通过热液流体的流入和流出的组分。几种类型的绿泥石化反应（包括黑云母绿泥石化）可以通过它们与Al 3+、Fe 2+、Mn 2+和Mg 2+的流入和H4 SiO 4、Ca 2+、K+和F-的流出的反应来表征。角闪石绿泥石化（64-54 Ma，330-190 °C）、钾长石绿泥石化（68-53 Ma，350-210 °C）、充填岩沉淀（66 ~ 63 Ma，340 ~ 320 °C）的时代和热条件与黑云母绿泥石化（68-51 Ma，350-180 °C）的时代和热条件重叠。绿泥石化反应（本研究和Yuguchi等人，2015年）和斜长石蚀变（Yuguchi等人，2019年a）代表了在68至51 Ma的时间条件下，随着温度从350 ° C降至180 °C，流体化学的连续变化。随着蚀变的进行，热液中铝、铁、锰、镁离子的浓度逐渐降低，钙、氢、氟离子的浓度逐渐升高。角闪石绿泥石化与磁铁矿和钛铁矿的形成有关。磁铁矿和钛铁矿形成的热液条件可以通过其伴生矿物周围的硫化物的化学特征来解释。磁铁矿的形成温度高于钛铁矿的形成温度，表明热液流体中氧逸度随温度从280-310 °C降低到220-250 °C而降低。
Abstract This study, along with our previous studies (Yuguchi et al. 2015, 2019a), reveals the hydrothermal alteration processes in a pluton, with a focus on the mass transfer between minerals and hydrothermal fluid. It also depicts the sequential variations in fluid chemistry as alteration progresses. Hydrothermal alteration of the Toki granite in Tono, Japan—the study area of this research—progressed through the successive processes of chloritization, plagioclase alteration, and precipitation of a carbonate. This paper describes the alteration processes of hornblende chloritization, K-feldspar chloritization, and the formation of fracture-filling chlorite through petrography and mineral chemistry. A set of singular value decomposition analyses was conducted to obtain reaction equations for the chloritization processes, which facilitates the quantitative assessment of mass transfer between the reactant and product minerals, and the inflow and outflow of components through the hydrothermal fluid. Several types of chloritization reactions (including biotite chloritization) can be characterized by their reaction with the inflow of Al3+, Fe2+, Mn2+, and Mg2+ and the outflow of H4SiO4, Ca2+, K+, and F–. The age and thermal conditions of hornblende chloritization (64–54 Ma and 330–190 °C), K-feldspar chloritization (68–53 Ma and 350–210 °C), and precipitation of fracture-filling chlorite (66 and 63 Ma, 340 and 320 °C) overlap with those of biotite chloritization (68–51 Ma and 350–180 °C). The chloritization reactions (this study and Yuguchi et al. 2015) and plagioclase alteration (Yuguchi et al. 2019a) represent sequential variations in fluid chemistry at temporal conditions from 68 to 51 Ma as the temperature decreased from 350 to 180 °C. As the alteration proceeds, the concentrations of aluminum, iron, manganese, and magnesium ions in the hydrothermal fluid decrease gradually, and those of calcium, hydrogen, and fluorine ions increase gradually. Hornblende chloritization is associated with formation of magnetite and ilmenite. The thermal conditions of the hydrothermal fluid yielding the formation of magnetite and ilmenite can be interpreted by the chemical characteristics of chlorite around their associated minerals. The formation temperature of magnetite was higher than that of ilmenite, implying a decrease in oxygen fugacity in the hydrothermal fluid with the decrease in temperature from 280–310 to 220–250 °C.