Late-stage exhumation of metamorphic core complexes and landscape development during orogenic collapse of the North American Cordillera

Toraman, Erkan University of Minnesota 2014 해외박사(DDOD)

Exogenic and endogenic processes control the exhumation of partially molten crust in extending orogens. Their relative contribution to total denudation is critical to evaluate different tectonic models. Therefore, assessing the timing, rates, style, and conditions of events from melt crystallization to cooling at near-surface temperatures is significantly important for understanding the thermo-mechanical evolution of orogenic crust and linking deep-to-shallow processes. Metamorphic core complexes (MCC) and gneiss domes located within the hinterland of orogenic belts expose a significant quantity of former partially-molten mid-to-lower crust in the form of migmatites. The Thor-Odin, Frenchman's Cap, and Okanogan domes are exposed in the biggest Cordilleran-style metamorphic core complex, the Shuswap MCC, where a series of migmatitic gneiss domes formed during collapse of the thickened crust in the Cenozoic. The Thor-Odin and Frenchman's Cap domes form the Shuswap MCC's narrow northern end where the present day topographic relief reaches up to 2.5 km with deeply incised valleys and ubiquitous glacial features. The Okanogan dome, on the other hand, represents the wider, lower-relief (≤ 1km) southern termination. In the Thor-Odin and Frenchman's Cap domes, zircon U-Th/He ages range from 45 to 37 Ma. Apatite fission track ages range between 48 to 14 Ma and increase with increasing sample elevation. Thermal modeling of samples from higher altitudes (~2100 to 1800 m) verify only rapid Eocene cooling, whereas the lower-elevation samples (~1800 to 500 m) reveal an additional Plio-Quaternary cooling event. The presence of the top of a fossil Eocene partial annealing zone at ~1800 m indicates that the migmatite dome reached near-surface depths (1-2 km) during its initial exhumation mainly by detachment tectonics. Apatite U-Th/He chronometry of these samples yields Miocene (26-5 Ma) ages. A number of low elevation (~500 m) samples collected from valleys reveal intra-sample single grain U-Th/He ages. Combined with the results of thermal modeling, these age variations indicate a rapid exhumation pulse at ca. 3 Ma, possibly related to continental glaciation. In the Okanogan dome, zircon U-Th/He ages range from 51 to 41 Ma and decrease towards the detachment fault zone, emphasizing up to 3.7 km/myr slip rate on the detachment zone. Apatite fission track and U-Th/He ages vary from 51 to 23 Ma, recording a very slow phase of erosional exhumation of the dome that removed ~ 2 km of rocks subsequently after its initial rapid ascent facilitated by detachment tectonics in the Eocene. Low-temperature data also document different cooling paths of rocks depending on their structural level; rocks closer to the detachment zone display rapid cooling rates (≥ 100 °C/myr), whereas deeper structural levels cool slowly (10-30 °C/myr). As in the North American Cordilleran hinterland, a series of migmatite-cored metamorphic core complexes is exposed in the Hellenides, where the geodynamic context of migmatitic dome formation is well known from previous research. Multiple low-temperature thermochronologic techniques combined with existing structural, geo- and thermochronologic, and petrologic data from Cordilleran and central Aegean migmatitic gneiss domes document rapid ascent of partially molten mid-to-lower crustal rocks, facilitating significant mass and heat advection to the shallow crust. Heat advection results in a high-geothermal gradient in shallow crust and shifts the brittle-ductile transition zone close to the surface. Percolation of surface-derived fluids through fault and fracture zones enables rapid cooling of rocks and enhances the brittle rheology.

The Sound of the Sea All the Time: Landscape and Image as Method

Toraman, Zeynep Harvard University ProQuest Dissertations & Theses 2023 해외박사(DDOD)

This dissertation presents a collection of essays, musical compositions and program notes written between 2017 and 2023. To overcome the methodological and representational limitations the portfolio-based dissertation format poses, I present my musical compositions alongside essays and program notes, combining my musical and textual output into a single research product.Theodor W. Adorno's 1928 essay on Franz Schubert, in which Adorno evokes a fictional landscape to stage and examine Schubert's distinct compositional practice, serves as my starting point to explore landscape (and seascape) as both an object of study and a method of observation. The dialectical image, constructed in that essay via the physiognomy and narrative experience of the landscape, conceptually dramatizes a critical viewpoint. I consider the nature of this and other such images in their 'historicity' as theorized and developed throughout the critical and analytical practices of Adorno and Walter Benjamin. Critical to the Schubert Essay in particular is Adorno's looking past the overly romanticized interpretations of the composer, and his insistence that the meaning of this music can only be revealed if we look past such interpretations and focus on its truth content, which appears only through its decay.In my project - which presents itself at once as a comparative reading and also as a series of micro-fantasies - unanswered, or indeed unarticulated questions, regarding narrative and indeterminacy are evoked in an act of authorial self-determination haunted principally by the musical specters of the nineteenth-century chamber music and orchestral repertoires. The depth and the limitations of nineteenth-century romantic imagination, its ambiguities and paradoxes between subject and object, between natural and supernatural, between ideal and material, between transparency and opacity, are further developed in my compositional work, as the themes of indeterminacy and complexity are explored through my approach to musical form and content. Direct and indirect quotations and glosses of historical musical materials, retrieved through a process analogous to the research of archival fragments, are woven into the fabric of each piece allowing me to engage with the Western classical music canon in a curious but kind manner where bonds are formed based on mutuality and empathy with this history. The veiling and unveiling process that Adorno identifies in Schubert's music in which 'the instant a material concretizes and becomes recognizable it has already disappeared' is a process analogous to the one that Michel Serres describes when he writes, "Unveiling does not consist in removing an obstacle, taking away a decoration, drawing aside a blanket under which lies the naked thing, but in following patiently and with respectful diplomacy the delicate disposition of the veils, zones, neighboring spaces, the depth of the pile, the talweg of their seams and in displaying them when possible, like a peacock's tail or a lace skirt." It is through this process that these gleaned fragments and musical idioms are exposed in my music, rendered unrecognizable and always slightly out of reach, veiled in mist and enveloped clouds.Following from such a 'delicate disposition,' my approach to musical form uses "the Idiot's formula," as developed by Jalal Toufic in his reading of Dostoevsky, as its poetic principle. Toufic writes, drawing on Gilles Deleuze, that Dostoyevsky's characters, who are constantly caught up in life-and-death emergencies, even while they are caught up in these intense moments know that there is a more urgent question, but they do not know what it is. This awareness is what stops them and makes them become disoriented. This is the Idiot's formula. With this image in mind, I design musical forms through which each moment delivers this narrative tension, propelling the form forward, making each moment singular while preserving a sense of unity, yet also rendering this unity completely meaningless because the tension is an illusion, and the music is in fact going nowhere. The bigger formal question is left unarticulated.The compositions and essays presented in this dissertation render this dynamic, as it relates to nineteenth-century poetics, explicit through an approach to composition and writing as curatorial practice and a mode of rhizomatic organization in which each of my works portrays both an archive and its curator at once. My methodology reflects my dedication to embracing unresolved tensions, refusing to let the complexity thin out, and allowing for the coexistence of multiple perspectives and lines of thought.