Element mobility and scale of mass transport in the formation of quartz veins during regional metamorphism of the Waits River Formation, east-central Vermont
Element mobility and scale of mass transport in the formation of quartz veins during regional metamorphism of the Waits River Formation, east-central Vermont
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DOI：
10.2138/am.2008.2461
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发表时间：
2008
影响因子：
3.1
通讯作者：
S. Penniston‐Dorland;J. Ferry
中科院分区：
文献类型：
--
作者：
S. Penniston‐Dorland;J. Ferry
摘要对韦茨河组中的脉和邻近蚀变边缘进行了研究，以确定相关的质量传递主要是由于大尺度平流还是小尺度扩散。从泥质岩和碳酸盐岩宿主中最早和最多代的矿脉中采集矿脉、边缘和邻近围岩的样品，这些矿脉来自于岩石和蓝晶石带的露头。采用由Zr、Ti、REE和U组合定义的参照系，对边缘和未蚀变围岩的整体成分进行了比较。相对于未蚀变的围岩，两个露头的边缘通常表现出Si、K、Ba和Rb的损失。蓝晶石带边缘显示镁和铯的损失。脉边系统作为一个整体与相邻的未蚀变围岩之间的K、Ba、Rb、Cs和Mg的差异可能是脉中云母发育的原因。加入到脉中的Si和Ca不能通过从布边去除Si和Ca来平衡。脉边系统比围岩含有更多的Si，总体上，向蓝晶石带和蓝晶石带分别增加了1.40 mg Si/cm 3和1.55 mg Si/cm 3。硅在露头尺度上的质量平衡要求石英脉中>90%的硅来自外部。石英脉研究形成主要是由流体流动和大规模的对流传质与相对较小的组成部分，局部质量传输扩散。在整个露头的矿脉中产生所观察到的石英量所需的时间积分流体通量估计为102 -6·106 cm 3流体/cm 2岩石。石榴石中的矿物包裹体和断裂的石榴石附近的静脉表明，形成的边缘和静脉开始前形成的石榴石和石榴石生长结束后继续。
Abstract Veins and adjacent alteration selvages in the Waits River Formation were investigated to determine whether associated mass transfer was due primarily to large-scale advection or small-scale diffusion. Samples of the vein, selvage, and adjacent wall rock were collected from the earliest and most numerous generation of veins in pelite and carbonate hosts from outcrops in the chlorite and the kyanite zones. Bulk compositions of selvages and unaltered wall rocks were compared using a reference frame defined by a combination of Zr, Ti, REEs, and U. Selvages from both outcrops typically exhibit losses of Si, K, Ba, and Rb relative to unaltered wall rock. Kyanite zone selvages show losses in Mg and Cs in addition. Differences in K, Ba, Rb, Cs, and Mg between the vein-selvage system as a whole and adjacent unaltered wall rock are possibly accounted for by development of micas in veins. The addition of Si and Ca to veins is not balanced by removal of Si and Ca from the selvages. Vein-selvage systems contain more Si than wall rock, with an overall addition of ≈40 mg Si/cm3 to the chlorite zone and ≈55 mg Si/cm3 to the kyanite zone. Mass balance of Si at the outcrop scale requires that >90% of the Si in quartz veins was derived externally. Quartz veins studied formed primarily by fluid flow and large-scale advective mass transfer with a relatively minor component of local mass transport by diffusion. The estimated time-integrated fluid flux necessary to produce the observed amount of quartz in veins in an entire outcrop is ≈2-6·106 cm3 fluid/cm2 rock. Mineral inclusions in garnet and fracturing of garnets adjacent to veins indicate that formation of selvages and veins initiated prior to formation of garnet and continued after the end of garnet growth.