Deep crustal growth of quartz, kyanite and garnet into large-aperture, fluid-filled fractures, north-eastern Connecticut, USA
Deep crustal growth of quartz, kyanite and garnet into large-aperture, fluid-filled fractures, north-eastern Connecticut, USA
复制标题
DOI：
10.1111/j.1525-1314.1995.tb00220.x
复制
发表时间：
1995-03
影响因子：
3.4
通讯作者：
J. Ague
中科院分区：
文献类型：
--
作者：
J. Ague
对康涅狄格州东北部Merrimack向斜异常保存完好的热液脉进行了岩石学和岩石学分析，以便对下大陆地壳的裂缝孔径尺寸和孔隙度进行新的野外约束。脉体在露头保留了大量的开放空间，并含有石英、蓝晶石和富铝石榴石的半面体到自面体晶体等矿物组合。纹理证据明确表明，脉状矿物生长在脉壁之间的宏观（毫米至厘米尺度）开放空间中。脉体为大孔径裂缝，发生了明显的对流渗流和化学反应。今天，由于裂缝壁之间的开放空间，岩体的孔隙率为0.3%，但在流动系统活跃时，它可能高达几个百分点。脉状矿物组合的定量热压测量结果表明，裂缝形成的压力和相应的地壳深度为0.8 GPa和0.3 km，温度为550 ~ 600℃，裂缝形成的深度与阿卡迪亚造山运动期间梅里马克向斜的最大埋藏深度相对应。大孔径裂缝的形成可显著增加深部地壳的瞬态渗透率，从而影响变质传热传质。
A petrographic and petrological analysis of exceptionally well-preserved hydrothermal veins from the Merrimack synclinorium, north-eastern Connecticut, has been carried out in order to place new field-based constraints on fracture aperture dimensions and porosity in the lower continental crust. The veins preserve substantial open space today in outcrop, and contain mineral assemblages including subhedral to euhedral crystals of quartz, kyanite and almandine-rich garnet. Textural evidence indicates unequivocally that the vein minerals grew into macroscopic (mm- to cm-scale) open space between the vein walls. The veins are interpreted to have been large-aperture fractures along which significant advective fluid infiltration and chemical reaction occurred. The porosity of the rock mass due to open space between fracture walls today is c. 0.3%, but it could have been as large as several percent when the flow system was active. Quantitative thermobarometry results from vein mineral assemblages indicate that the fractures formed at pressures and corresponding crustal depths of c. 0.8 GPa and c. 30km, and temperatures of 550–600° C. The depth of fracture formation corresponds to published estimates of the maximum burial depth of the Merrimack synclinorium during the Acadian orogeny. The formation of large-aperture fractures could increase significantly the transient permeability of the deep crust, and therefore influence metamorphic heat and mass transfer.