IGCP 524 Excursion on Arc-Continent Collision – some geological highlights

Following a 2-day conference at the National Cheng-Kung University in Tainan, we participated in a 5-day field trip in the framework of the IGCP (International Geological Correlation Program) 524 Project on Arc-Continent Collision.

The itinerary led us from Tainan down to the southern Hengchun Peninsula, then from the southernmost tip of Taiwan north along its highly picturesque east coast. We visited the Coastal Range itself and the very linear Longitudinal Valley between Taitung and Hualien. Northwest of Hualien, we then went into the Taroko Gorge, an area of supreme natural beauty, indeed! From the Taroko Gorge we started our journey back to Taipei along the long, winding and often quite narrow coastal highway.




Hengchung Peninsula

At the beginning of our excursion, we visited outcrops of the Kenting Melange on the southern tip of the Hengchun Peninsula. We were not able to see the ultramafic rocks within this mélange in any outcrop, so we instead had to besiege a peridotite used for erecting a monument near Hengchung.



The Sheting Nature Park at the eastern coast of southernmost Taiwan offered us some superb exposures of turbiditic sandstones … plus lots of wind gusts that brought the waves crashing in on the coast.



While arguing with John on the sandstone petrography didn’t bring Kamil out of his balance yet, the strong gusts of wind higher up at a scenic stop a little later certainly did!




Back in Hengchung, we visited the Hengchung Western Hills, The topography of these hills was created by the uplift of Pleistocene (sic!) limestones. The hills slope gently eastwards. The Taiwanese geologists explain their uplift by active west-vergent thrusting just off the coast.



Coastal Range

This part of the trip gave us insight into the processes related to the collision of the Luzon Island Arc with the Eurasian continental margin. On a traverse through the Coastal Range along road no. 23 between Tungho and Fuli, we crossed a NNE-trending syncline. The predominantly igneous rocks in the structurally deeper part build up the high topography, whereas the predominantly finegrained, volcaniclastic and easily erodable forearc sediments in the core of the syncline form nicely arable land with lots of plantations. The picture was taken near Shihoang, looking south.

The largely volcaniclastic, grain-supported conglomerates immediately overlying the igneous succession feature very systematically E-W-trending, subvertical fractures related to E-W-shortening. Coral fragments stem from reefs fringings the volcanic edifices.





... and all along the Coastal Range, we encounter the very enigmatic Lichi Melange. Its origin (real tectonic mélange or olistostrome) caused longlasting debates among all excursion participants ....



Active faults in the Longitudinal Valley

A traverse across the south-draining Peinan River near Kuanshan offered a nice view across the wide Longitudinal Valley. Actually, this wide, braided river is rather atypical of the valley, as it hosts a great number of rice terraces. The Kuanshan rice has a very high reputation, of which we were fully convinced after enjoying a meal at a local restaurant.


And then, finally, finally, we saw a truly active structure: the Chihshang fault! This blind thrust is creeping mostly aseicmically – at a rate of 2 cm per year in horizontal and in vertical direction! On the photo, you see Micha standing on a concreted wall of a river channel, which was built 13 years ago (The green bar is an extensiometer installed by the Central Geological Survey of Taiwan). This wall shows a rupture induced by an upwarping fold at the tip of the Chihshang fault. The once circular water tube is visibly flattened. (See, Adrian, that’s how active structures should look like!!! ;-> )



Taroko Gorge

In the deeply incised Taroko Gorge, the metamorphic rocks of Taiwan (the Tananao Complex) are exposed. Marbles, quartzites, greenschists and granitic intrusions show fantastic large- and small-scale structures that are very attractive, even for non-geologists.