Pleistocene onset of rapid, punctuated exhumation in the eastern Central Range of the Taiwan orogenic belt

Abstract

The Taiwan orogenic belt is often treated as a steady, southward-propagating orogenic system with an essentially constant erosion rate of 4–6 mm/yr over the past 5 m.y. We present 4 new age-elevation transects from the Central Range based on 19 new and 86 previously published fission track and (U-Th)/He dates of completely reset detrital zircon and apatite grains. The age-elevation curves and thermal models imply slow cooling prior to ca. 2–1.5 Ma (at exhumation rates of ∼0.1 mm/yr), an increase in exhumation rates from ca. 2–1.5 Ma to ca. 0.5 Ma (2–4 mm/yr), and possibly a further acceleration in exhumation from ca. 0.5 Ma to present (4–8 mm/yr). Three transects from three different latitudes in the eastern Central Range yield similar results, each showing punctuated exhumation with progressively faster rates.

Tidal Modulation and Tectonic Implications of Tremors in Taiwan

“…The distributions of tremors identified here correlate with the south to north transition from relatively thin to thick continental crust and extend from near the crust‐mantle boundary to the upper‐middle crust, forming a steep, east dipping oblate ellipsoid (Figure ). The steep dip of the cluster is consistent with the nearly vertical structure interpreted from low‐frequency seismic events by Aguiar et al () and with the abundance of steep faults and foliations observed in the Central Range (Hsu et al, ). A steep structure is also more efficient in accommodating the high rates of exhumation cooling and rock uplift observed in the central part of the range (Ching et al, ; Hsu et al, ).…”

“…The steep dip of the cluster is consistent with the nearly vertical structure interpreted from low‐frequency seismic events by Aguiar et al () and with the abundance of steep faults and foliations observed in the Central Range (Hsu et al, ). A steep structure is also more efficient in accommodating the high rates of exhumation cooling and rock uplift observed in the central part of the range (Ching et al, ; Hsu et al, ). Modeling of tidal stresses and VLF seismic events, however, suggests a shallowly dipping structure (Ide et al, ).…”

Glacial buzzcutting limits the height of tropical mountains

“…The relatively constant peak elevation and width of the Central Range and its thermal 25 history are thought to be an indication of topographic and flux steady state for the northern 150 km of the range (Willett and Brandon, 2002;Stolar et al, 2007). Recent work has countered this idea by putting forth the case that a rapid increase in exhumation rate occurred along the entire strike of the range starting between 1-2 Ma (Hsu et al, 2016). Low-relief surfaces found at high elevations (above 3000 m) in Taiwan are thought to be remnants of an eroded surface formed sometime prior to 1-2 Ma (Ouimet et al, 2015).…”

“…15 Virtually every assessment of the glacial buzzsaw has passed over the tropics, with the notable exceptions of the extensively glaciated Cordillera Blanca of Peru (Margirier et al, 2016) and the Rwenzori Mountains of Uganda (Ring, 2008). The highlands of every continent straddling the tropics were glaciated during the global Last Glacial Maximum (gLGM) (Hastenrath, 2009), and likely during other intermediate cold phases throughout the Pleistocene (Porter et al, 1989), but glacial erosion has been discounted as a factor in limiting 20 the height of the majority of these mountain ranges (e.g., Egholm et al, 2009;Morell et al, 2012;Herman et al, 2013;Hsu et al, 2016). An obvious reason for excluding the tropics from the list of glacially buzzcut ranges is that their hypsometry, on the gross scale, shows very little area near the lower-limit of the Pleistocene ELA, and significant hypsometric maxima several km below it (Egholm et al, 2009).…”

Dating palaeo‐seismic faulting in the Taiwan Mountain Belt

“…The minimum temperature of 750°C for pseudotachylite generation, as inferred from petrographical observations (Chu et al., ; Kuo, ), is considered sufficient to degas preexisting 40 Ar* (Sherlock et al., ). Post‐faulting thermal resetting of pseudotachylite 40 Ar/ 39 Ar ages is ruled out since it would require over 10 Ma residence at 220°C for biotite microlites (Sherlock, Watts, Holdsworth, & Roberts, ), while the regional thermal history in this period was characterized by rapid cooling during fast exhumation (Hsu et al., ) without magmatic or prograde metamorphic effects causing significant Ar loss. Therefore the results correspond to brittle faulting events experienced by the deeply‐exhumed metagranite body and the basement complex during the retrograde path (Chu et al., ).…”