斷層作用產生的假玄武玻璃是一個在大地震發生期間，圍岩因摩 擦加熱所形成的凝固熔融體，其可提供地震相關的物理參數而成為知 名的地震指示劑。一條蘊含假玄武玻璃之斷層被發現於臺灣東北的花 蓮和平地區且夾雜於大南澳花崗片麻岩之中。為了研究和平假玄武玻 璃對動態摩擦行為之影響及其相關機制，本研究利用和平鑽井的花崗 片麻岩的岩芯來進行高速岩石摩擦旋剪試驗。所有由低到高正向應力 (3 至30 MPa)的試驗數據皆顯示類似的摩擦行為趨勢，從初始滑移時 皆上升至一摩擦峰值μp (約0.6 至1.0)，而後隨著滑動距離的增加再 降至一穩態值μss (約0.3 至0.45)。顯著的是，在低正向應力(3 至9 MPa)的情況下，本研究發現在摩擦峰值後還有一摩擦緩坡之出現。掃 描式電子顯微鏡搭配能量色散X 光能譜分析儀和同步X 光繞射儀的 結果顯示階段性滑移摩擦試驗產生之熔融體皆有化學成分上之差異。 特別的是，穿透式X 光顯像儀分析之結果顯示各階段熔融帶中存在 的細小石英顆粒在數量上也有不同。這結果可能說明在Gibbs- Thomson 效應的影響下，熔融體中若有額外磨細作用及熱破裂之細顆 粒產物，會導致其黏滯度高於含有較少細顆粒之熔融體。本研究推測 這些伴隨在摩擦熔融中因熱力學作用所產生的細小粒狀材料，會造成 高黏滯度之熔融體，似乎會抑制斷層在地殼非常淺部之滑移，或是阻 礙地震在地表淺部初始破裂之滑動，即使熔融弱化在後續產生。;Fault-origin pseudotachylyte is a solidified melt produced by frictional heating during big earthquakes. It is well-known as a seismic indicator which can provide information on earthquake physics. A new locality of pseudotachylyte-bearing fault, hosted in the Tananao granitic gneiss, was discovered in the Hoping area of northeast Taiwan. To investigate the plausible dynamic frictional behavior of the Hoping pseudotachylyte, we perform rock friction experiments on granitic gneiss cores collected from the borehole in the Hoping area. All the mechanical data show similar frictional trends that the shear stress initially increases up to a peak value of ~0.6-1.0 (peak friction) and decreased with displacement to a steady state of ~0.3-0.45 from low to high normal stresses (3 to 30 MPa). It is notable that, at low normal stresses of 3 MPa, a transient increase of shear stress (friction bump) appears after peak friction. The micro-analytical results of the slip-stepping experimental products including in situ synchrotron XRD and FESEM-EDX show chemical and compositional variation in the matrix of melts. In particular, Transmission X-ray Microscope (TXM) on the matrix of melts shows the varied abundance of remain quartz grains in the melt layer. It suggests that melts with additive comminuted or thermal-cracking products result in higher viscosity than the one with less-abundant-relic melting, plausibly due to Gibbs-Thomson effect. We surmise that thermo-mechanical generated granular materials associated with frictional melting, resulting in high viscous melts, seem to terminate seismic slip at very shallow crust, or may hamper seismic slip in the initial earthquake propagation at shallow depth, even melt lubrication was operated afterword.
