Thermal history of rocks along the Totschunda and Denali faults with implications for exhumation, fault reactivation, and fault system evolution.

Author

Jacob Leo Rosenthal, Syracuse University

Date of Award

1-20-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Earth Sciences

Advisor(s)

Paul Fitzgerald

Keywords

Alaska;Fault;Strike Slip;Thermochronology

Subject Categories

Earth Sciences | Geology | Physical Sciences and Mathematics

Abstract

The main body of this research has focused on the tectonic evolution of the Totschunda fault and its relationship with the Denali fault in central Alaska. This dissertation is divided into three chapters that investigate questions surrounding the evolution of intersecting faults, reactivation of lithospheric structures, and the exhumation of crust surrounding these structures with an initial overview chapter that sets the context for the studied problems followed by a conclusions chapter that provides a summary of conclusions from this work. In the second chapter I document fault rejuvenation through thermal history modelling of multiple bedrock and detrital cobble samples along the margins of the southern Totschunda fault. This chapter incorporates a broad geologic history of the Totschunda fault, summarizes current research on this structure, and provides increased evidence of its reactivation and activity throughout the Miocene. I conclude that the Totschunda fault was most likely active in the early Miocene, with a rapid increase in activity following a ~6 Ma Pacific Plate vector change. In the third chapter my research applies low-temperature thermochronology with inverse thermal modeling to constrain the spatial-temporal cooling history of the Totschunda-Denali intersection region. I show that the apex of the block bounded by the Totschunda and Denali faults started to rapidly cool (>10°C/Ma) at roughly 25 Ma. Rapid cooling within the fault bounded block is symmetric and exceeds magnitudes of cooling in the surrounding country rock. I therefore link this 25 Ma rapid cooling with the formation of the fault intersection because both strands of the fault intersection would have had to be active and connected to accommodate vertical block motion between the two faults. I suggest the sub-vertical lithospheric scale strands of the Totschunda-Denali intersection facilitate vertical movement of the bound block under normal stress and that thermochronometric ages within the bound block may help constrain the age of other low angle fault intersection. The vertical extrusion of the bound block enables relative geometric stability of the junction during convergence changes by limiting fault system reorganization after the fault intersection forms. Therefore, I suggest that low angle (<25°) fault intersections may persist for tens of millions of years. In the fourth chapter, I focus on variations in exhumation along strike-slip faults. The patterns of exhumation along strike-slip or transpressional faults are often associated with restraining bends or an increase in obliquity to the direction of the converging plate. In this contribution, I document how two different fault pairs that delineate orogenesis along the Denali fault system are affected by convergence and propose additional models for exhumation along strike-slip faults by applying detrital apatite fission track (DAFT) thermochronology. I document that exhumation is structurally controlled and demonstrate how the distinct styles and lithospheric scales of the bounding faults led to different overall patterns of exhumation. In the first region, between the sub-vertical lithospheric scale Denali and Hines Creek faults, unimodal Late Miocene DAFT age populations document rapid exhumation in the narrow (~20 km width) block of crust between the two faults. In the second region, between the lithospheric Denali fault and low angle shallow crustal Granite Mountain fault, dominantly bi- and tri- modal DAFT age populations document Late Miocene and older Paleogene rock cooling. Here, exhumation is greatest along the Denali fault and decreases towards the Granite Mountain fault to the north in a broad distributed zone of deformation (~45 km width). Curvature of the Denali fault and obliquity of southern Alaska plate convergence is consistent along strike of the Denali fault segment in both regions; therefore, I suggest that the scale (lithospheric or continental) of the two fault pairs, rather than strike of the fault with respect to the convergence direction of the hanging wall, plays a greater role in controlling the patterns of exhumation and topographic development in the Eastern Alaska Range and also across other fault systems.

Access

Open Access

Recommended Citation

Rosenthal, Jacob Leo, "Thermal history of rocks along the Totschunda and Denali faults with implications for exhumation, fault reactivation, and fault system evolution." (2024). Dissertations - ALL. 1860.
https://surface.syr.edu/etd/1860