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