| Autor: |
Cao, Yi, Du, Jinxue, Park, Munjae, Jung, Sejin, Park, Yong, Kim, Dohyun, Choi, Seungsoon, Jung, Haemyeong, Austrheim, Håkon |
| Předmět: |
|
| Zdroj: |
Journal of Geophysical Research. Solid Earth; May2020, Vol. 125 Issue 5, p1-33, 33p |
| Abstrakt: |
The eclogite in the Flem Gabbro from Flemsøya Island of the Western Gneiss Region in Norway contains atypical eclogitic minerals, such as olivine and orthopyroxene, and can be texturally divided into weakly deformed massive eclogite (MEC) and strongly deformed foliated eclogite (FEC). Based on phase equilibria modeling, peak metamorphic pressure‐temperature conditions of ~600–750 °C and ~1.0–2.5 GPa and ~700–820 °C and ~2.7–3.7 GPa are recorded in MEC and FEC, respectively. These different pressure‐temperature conditions between MEC (high‐pressure, HP) and FEC (ultrahigh‐pressure, UHP) in the same outcrop reflect deformation‐enhanced eclogitization metamorphism (HP to UHP transition) via the addition of external water during subduction/burial to early exhumation stages and metastable preservation of the HP MEC assemblage at UHP condition due to the local lack of deformation and fluid access at the deep subduction interface or around Moho beneath continental collision zone. Based on the mineral microstructures, nondislocation‐based creep mechanisms—such as diffusion creep, grain and phase boundary sliding, and rigid‐body‐like rotation—play dominant roles in governing the deformation features of FEC and developing the crystal preferred orientations of its major constituent minerals. These deformation mechanisms could considerably affect the interplate coupling at the subduction interface or the rheological strength of Moho beneath continental collision zones. Therefore, the effects of metastability‐based (i.e., preservation of low‐pressure assemblages at HP conditions) and contributions of nondislocation‐based creep mechanisms should be included in the future geodynamic and petrological simulations of subduction and collision processes. Plain Language Summary: Eclogite is a unique metamorphic rock that forms at high pressure and indicates deeply subducted crust or thick continent crust around Moho depth. Under tectonic forces, such high‐pressure rocks can be exhumed and exposed in some current orogenic belts, such as the eclogite in the Flem Gabbro from Flemsøya Island of the Western Gneiss Region in Norway. Based on an integrated study, we acquired two key findings from this eclogite. First, due to lack of deformation and fluid access, the weakly deformed massive type of eclogite is metastable at the higher pressure and temperature condition where strongly deformed foliated type of eclogite is stable. Second, mineral microstructures suggest that the deformation is mainly accommodated by nondislocation‐based creep mechanisms, such as diffusion creep, grain and phase boundary sliding, and rigid‐body‐like rotation, which produce weak crystal preferred orientations of major phases. The influences of metastability and nondislocation‐based creep mechanisms are believed to be important but rarely addressed in the current geodynamic and petrological simulations of subduction and collision processes. This study points out some concerns and directions for future numerical modeling studies. Key Points: Massive and foliated eclogites from the same outcrop have contrasting peak P‐T conditions, suggesting metastabilityMicrostructures of the major minerals in foliated eclogites indicate dominantly nondislocation‐based creep mechanismsMetastability and nondislocation‐based creep mechanisms are suggested to be included in future geodynamic modeling [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
Plný text