Figure 4: Compiled geochronology and thermochronology from Lime Creek Bedrock. AHe, AFT, and zircon U-Pb ages are displayed in colors coded in the key. Faults are denoted as solid lines or dotted where inferred. Small camera images and corresponding white letters denote image locations in Figure 6. For sample 19SOLO06, the dashed green line leading away from the sample location denotes inferred sample path for a rock that clearly originated from the outcrop denoted with a green X. Representative thermal model for each side of the Totschunda fault shows that more recent rapid cooling occurred on the west side of the Totschunda fault than the east side of the structure.

4.1 LA-ICP-MS U-Pb Zircon Data

The U-Pb zircon ages for the hypabyssal bedrock in the Lime Creek drainage range from ca. 25 to 28 Ma (Table 1; S1, S2) and therefore these intrusions are associated with the Wrangell volcanic arc (Trop et al., 2022). The gabbro bedrock we sampled (19SOLO01 and 19SOLO02) was previously mapped as Triassic but our new data indicates this unit is Cretaceous in age (ca. 100 Ma). Gabbro units mapped as Triassic in the Lime creek area and within the McCarthy and Nabesna map areas (MacKevettt, 1978; Richter, 1971) may warrant further inquiry to verify and better understand the spatial extent of Chisana arc Cretaceous aged magmatism (Manselle et al., 2020) in the region.
The cobbles we analyzed likewise have lithologies (porphyritic volcanics) and Oligocene-Miocene ages showing they too originated from Wrangell volcanic arc centers (e.g., Richter et al., 1990; Trop et al., 2022) (Figure 6; Tables 1, S1, S2). U-Pb ages for the felsic/intermediate detrital cobbles from the White River ’Tillites’ are primarily from two populations: the first group consisting of three cobbles ranged in age from ca. 26 to 28 Ma and a second group consisting of four cobbles (from two locations) ranged in age from ca. 8.9 to 10 Ma (Figure 6).

4.2 Fission Track Data: bedrock samples and Late Miocene-Pleistocene detrital cobbles