Meteoric water circulation in a rolling-hinge detachment system (northern Snake Range core complex, Nevada)

Abstract

Combined petrofabric, microstructural, stable isotopic, and 40 Ar/ 39 Ar geochronologic data provide a new perspective on the Cenozoic evolution of the northern Snake Range metamorphic core complex in east-central Nevada. This core complex is bounded by the northern Snake Range detachment, interpreted as a rolling-hinge detachment, and by an underlying shear zone that is dominated by muscovite-bearing quartzite mylonite and interlayered micaschist. In addition to petrofabric, microstructural analysis, and 40 Ar/ 39 Ar geochronology, we use hydrogen isotope ratios (δD) in synkinematic white mica to characterize fl uid-rock interaction across the rolling-hinge detachment. Results indicate that the western fl ank of the range preserves mostly Eocene deformation (49-45 Ma), characterized by coaxial quartz fabrics and the dominant presence of metamorphic fl uids, although the imprint of meteoric fl uids increases structurally downward and culminates in a shear zone with a white mica 40 Ar/ 39 Ar plateau age of ca. 27 Ma. In contrast, the eastern fl ank of the range displays pervasive noncoaxial (top-tothe-east) fabrics defi ned by white mica that formed in the presence of meteoric fl uids and yield Oligo cene-Miocene 40 Ar/ 39 Ar ages (27-21 Ma). Evolution of the Oligocene-Miocene rolling-hinge detachment controlled where and when faulting was active or became inactive owing to rotation, and therefore where fl uids were able to circulate from the surface to the brittle-ductile transition. On the western fl ank (rotated detachment), faulting became inactive early, while continued active faulting on the eastern fl ank of the detachment allowed surface fl uids to reach the mylonitic quartzite. The combined effects of synkinematic recrystallization and fl uid inter action reset argon and hydrogen isotope ratios in white mica until the early Miocene (ca. 21 Ma), when the brittle-ductile transition was exhumed beneath the detachment. GEOLOGICAL SETTING AND PREVIOUS WORK The northern Snake Range detachment defi nes the Snake Range metamorphic core complex in east-central Nevada (Fig. 1), which resulted from Oligocene-Miocene extension of the Basin and Range Province (Wernicke, 1981;

Eocene and Miocene extension, meteoric fluid infiltration, and core complex formation in the Great Basin (Raft River Mountains, Utah)

“…Undoubtedly, Miocene Basin and Range extension played a major role in establishing the present‐day architecture of crust and lithospheric mantle underlying the Great Basin. However, there is increasing evidence that deformation structures preserved in the exhumed mylonitic footwall of MCCs may preserve geological information that dates back to earlier episodes of their tectonic history [e.g., Wells et al ., , ; Foster et al ., , ; Gébelin et al ., , ; Vogl et al ., ; Wong et al ., ]. This also holds true for the RAG‐MCC where middle to late Miocene exhumation along the RRDSZ was associated with unroofing and doming of the MCC postdating Oligocene intrusion of plutons [e.g., Wells et al ., ; Konstantinou et al ., ].…”

“…Localized synextensional interaction of mylonitic footwall rocks with surface‐derived fluids is a common feature of extensional detachment systems bounding high‐grade MCCs of the western United States [e.g., Kerrich , ; Fricke et al ., ; Wickham et al ., ; Mulch et al ., , , ; McFadden et al ., ; Gottardi et al , ; Gébelin et al , , , ] and has recently been documented in similar environments for other orogens such as the European Alps [ Campani et al ., ], the South Tibetan Detachment [ Gébelin et al ., ], the Alpine Fault [ Menzies et al ., ], or the Menderes MCC [ Hetzel et al ., ]. The infiltration of meteoric water into brittle fault zones and strongly localized fluid flow down to the brittle‐ductile transition have been detected mainly by low hydrogen ( δ 2 H) and oxygen ( δ 18 O) isotope ratios in recrystallized hydrous minerals of mylonitic shear zones [e.g., Fricke et al ., ; Wickham et al ., ; Famin et al ., ; Mulch et al ., , ].…”

Timing and conditions of brittle faulting on the Silltal-Brenner Fault Zone, Eastern Alps (Austria)

“…Low dD in white micas (dD \-80 %) can only be explained by hydrogen isotope exchange with a meteoric fluid with low dD values (e.g. Gébelin et al 2015) and an important influence of meteoric water in samples BF1 and BF2 is thus clearly established. For both gouge samples, a well-defined linear relationship between dD values and K-Ar (apparent) ages is observed (Fig.…”

New parametric implementation of metamorphic reactions limited by water content, impact on exhumation along detachment faults

“…b -Modified after Jolivet and Goffé (2000). zone (Gébelin et al, 2015;Marquer and Burkhard, 1992;Patriat and Jolivet, 1998). The contrasting local H 2 O conditions associated with low-strain/high-temperature and high-strain/low-temperature paragenesis demonstrate that some major retrograde reactions are limited by the absence of fluid reactants (Goncalves et al, 2012;Oliot et al, 2014).…”