Lawsonite composition and zoning as tracers of subduction processes: A global review
Lawsonite composition and zoning as tracers of subduction processes: A global review
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DOI：
10.1016/j.lithos.2020.105636
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发表时间：
2020-10
期刊：
影响因子：
3.5
通讯作者：
D. Whitney;K. Fornash;P. Kang;E. Ghent;L. Martin;A. Okay;A. V. Brovarone
中科院分区：
文献类型：
--
作者：
D. Whitney;K. Fornash;P. Kang;E. Ghent;L. Martin;A. Okay;A. V. Brovarone
劳森石是一种丰富的含水矿物，存在于大多数俯冲带的~45 - 300 km深度的洋壳、沉积物和交代岩中，但在地质记录中很少保存，因为它通常在俯冲或退变质过程中转化为绿帘石和其他矿物。由于在俯冲带的水和元素循环的硬柱石的意义，新鲜的硬柱石蓝片岩，更罕见的是，榴辉岩的出现提供了重要的机会，以确定硬柱石组合物，分区，包套，并利用这些信息来重建俯冲和折返过程中的反应历史。在这篇综述中，我们使用新的和已发表的数据来记录硬毛钠石组合物中的八个已知的硬毛钠石榴辉岩的地方，其中新鲜的硬毛钠石与石榴石+绿辉石共存的岩石基质，以及硬毛钠石夹杂物的组合物中的六个已知的网站，其中硬毛钠石只发生在石榴子石夹杂物中的榴辉岩相岩石，缺乏基质硬毛钠石。由于硬硅钙石蓝片岩比硬硅钙石榴辉岩更常见，我们调查了硬硅钙石在蓝片岩的代表性地区的组成，包括与榴辉岩（硬硅钙石轴承，绿帘石轴承），蓝片岩不与榴辉岩在当前的曝光水平。包括变质玄武岩，富硅和碳酸盐的变质沉积岩，交代岩，和硬铝石丰富的静脉。该数据集表明，硬柱石组合物是俯冲和折返过程中的反应历史的敏感指标，特别是流体-岩石相互作用，与俯冲带中的元素循环的影响。此外，大多数折返的硬铝榴辉岩记录板片表面的条件，对应的位置，板幔界面从耦合过渡到耦合，因此提供了关键的洞察俯冲带的热历史和动力学。
Lawsonite is an abundant hydrous mineral in oceanic crust, sediments, and metasomatic rocks at depths of ~45 to 300 km in most subduction zones, but it is rarely preserved in the geologic record because it commonly transforms to epidote and other minerals during prograde or retrograde metamorphism. Owing to the significance of lawsonite for water and element cycling in subduction zones, occurrences of fresh lawsonite in blueschist and, more rarely, eclogite provide important opportunities to determine lawsonite composition, zoning, and inclusion suites and to use this information to reconstruct reaction history during subduction and exhumation. In this review, we use new and published data to document lawsonite composition in eight of the nine known lawsonite eclogite localities in which fresh lawsonite coexists with garnet + omphacite in the rock matrix, as well as the composition of lawsonite inclusions in six of seven known sites in which lawsonite occurs only as inclusions in garnet in eclogite-facies rocks that lack matrix lawsonite. As lawsonite blueschist is much more common than lawsonite eclogite, we survey the composition of lawsonite in representative localities of blueschist, including blueschist associated with eclogite (lawsonite-bearing, epidote-bearing), and blueschist not associated with eclogite at current exposure levels. Included in this review are metabasaltic rocks, silica- and carbonate-rich metasedimentary rocks, metasomatic rocks, and lawsonite-rich veins. This dataset demonstrates that lawsonite composition is a sensitive indicator of reaction history during subduction and exhumation, and specifically of fluid–rock interaction, with implications for element cycling in subduction zones. Furthermore, most exhumed lawsonite eclogite records slab-surface conditions that correspond to the location where the slab-mantle interface transitions from decoupled to coupled, and therefore provides key insights into the thermal history and dynamics of subduction zones.