An in-depth look at distal Sierra Nevada palaeochannel fill: drill cores through the Table Mountain Latite near Knights Ferry

Abstract

The ,10.4 Ma Table Mountain Latite (TML) consists of high-K trachyandesite lavas that likely erupted from the Little Walker Center near Sonora Pass and flowed 80 miles (130 km) through the palaeo-Stanislaus river channel to Knights Ferry in the Sierra Nevada foothills. Complete sections through the proximal facies of the flow stratigraphy are common in the high-Sierra and along range-front faults, but in much of its distal facies in the Sierra Nevada foothills, the internal features of the unit are poorly exposed. Condor Earth Technologies offered us the opportunity to study three complete vertical sections through the distal facies of the TML through access to three drill cores. These cores, spaced 1500 0 (457 m) apart and oriented oblique to inferred flow direction by 308, are referred to here as cores A, B, and C, in a down-palaeoflow direction.Previous outcrop studies of the distal TML over the past century have concluded that the distal TML consists of a single flow. This is true of core B, which is dominated by a single 144 0 (44 m) thick flow, underlain by a thin (,5 0 , 1.5 m) flow with a vesiculated top, inferred to represent a toe of the thick flow, inasmuch as there is no baked zone or weathered contact between them. This contrasts sharply with core C, where the 50 0 (15.2 m) thick TML consists of four flows 5 -12 0 (1.6 -3.6 m) thick, each also defined by vesiculated tops, but differing in having weathered tops 1 -2 0 (0.3-0.6 m) thick, inferred to record an eruptive hiatus between each flow. The third flow in core C appears to be geochemically distinct from both overlying and underlying units, although all of the core samples are petrographically similar. The TML in cores C and B overlies coarse-grained andesitic volcaniclastic debris and fluvial deposits. By contrast, in core A, the TML overlies very fine-grained siltstones interpreted to record deposition in still water, probably a small lake produced by damming of the river by the thick flow in core B. The TML in core A is 20 0 (6 m) thick, and is composed of eleven 1 -3 0 (0.3-1.0 m) thick couplets, each consisting of a clay-altered hyaloclastite breccia passing upwards into a relatively fresh, nonbrecciated, vesiculated top. We interpret these couplets to represent thin toes of a flow that generated steam explosions when they came into contact with a standing body of water.Palaeomagnetic remanence data (inclination only) on lava flows from the cores are consistent with the Classic Table Mountain direction and inconsistent with directional results from any other Stanislaus Group lava flows published to date. Thus, by palaeomagnetic correlation, the lavas studied here were emplaced between 10.36^0.06 and 10.41^0.08 Ma. In addition, remanence results suggest that the three sampled flows from core C were erupted over a time period shorter than the secular variation rate (i.e. less than a few centuries) and the Knights Ferry portion of the TML was emplaced within several centuries of the average Classic TML age range

Miocene evolution of the western edge of the Nevadaplano in the central and northern Sierra Nevada: palaeocanyons, magmatism, and structure

“…In its earliest activity, it was likely the source for the second largest known lava flow unit in California (after the Lovejoy basalt), the 10.4 Ma Table Mountain Latite (Table 1). The Table Mountain Latite consists of voluminous trachyandesite to trachybasaltic andesite lavas (Putirka and Busby 2007) that flowed westward through palaeochannels in the central Sierra Nevada to the Central Valley (Ransome 1898;Slemmons 1953Slemmons , 1966Noble et al 1974;Priest 1979;King et al 2007;Gorny et al 2009;Koerner et al 2009;Pluhar et al 2009). Flow within palaeoriver channels is indicated by the presence of blocky jointing on the tops of some flows (Figure 6(k)), suggesting quenching by water, and stretching of vesicles parallel to the trend of the palaecanyon system ( Figure 5(l)).…”

“…In this paper, we interpret new field and geochronological results gathered by us and our students over the past five years, on Cenozoic strata and intrusions in the central and northern Sierra Nevada (Figures 2-7; Table 1; Roullet 2006;Busby et al 2008a,b;Garrison et al 2008;Gorny et al 2009;Hagan et al 2009;Koerner et al 2009). These results provide a sensitive record of the surface processes over the past , 50 Myr, including:…”

Extensional and Transtensional Continental ARC Basins: Case Studies from the Southwestern United States

“…That paleochannel funneled flows westward across the unfaulted Sierra Nevada block. One individual lava flowed at least 130 km westward (Gorny et al, 2009;Pluhar et al, 2009), an extremely unusual distance for an andesite, with a volume of 20 km 3 (the largest-volume intermediate-composition lava flow that I am aware of). The >200km 3 Table Mountain Latite lava flow field was erupted in only 28-230 kyr, between about 10.4 and 10.2 Ma (Busby et al, 2008a;Hagan, 2010;Putirka, 2010a, 2010b).…”

A tale of two Walker Lane pull-apart basins in the ancestral Cascades arc, central Sierra Nevada, California

“…6B). One of the Table Mountain Latite trachyandesite lavas is paleomagnetically correlated to the Sierra Nevada Foothills , forming a single flow unit of >25 km 3 (Gorny et al, 2009;Busby et al, 2013aBusby et al, , 2016. Flow-top breccias are common, but some flow tops are marked only by a vesicular horizon.…”

“…2) and located by global positioning system (GPS; see Supplemental Table S1 1 ). Although abundant field photographs and descriptions have been previously published (Slemmons, 1953(Slemmons, , 1966Noble et al, 1974;Busby et al, 2008a;Busby and Putirka, 2009;Gorny et al, 2009;Busby et al, 2013aBusby et al, , 2013bBusby et al, , 2016, this is the first paper to link outcrop photos (Figs. 6 and 10) with photomicrographs (Figs.…”