OUGS ME trip to China - August 1st to 10th 2011

Day 4, 5th August     Taishan: Where history meets geology.

Text Elisabeth d'Eyrames, Mike Molloy,
Photos Neil Lawley, Elisabeth d'Eyrames.

The aim of the day was to tackle Mount Tai, “the chief of the five Sacred Mountains” or the  “first mountain under Heaven”, altitude 1545, located at 36° 16′N and 117° 6′E. 6293. It is a  walkway of paved steps, some 30-40 metres wide on the lower parts, but getting narrower and steeper towards the top.

Nearly at the summit of Taishan
Nearly at the summit of Taishan

At five o’clock we passed the first gate and started walking on a path that has been used by pilgrims and famous emperors for 3000 years, thus Taoist temples have been erected all along the steps and some still in use. Since it is also a geopark, panels with geological explanations draw the attention of the walkers to the extraordinary history of the rocks.

What is most amazing is not that Mike walked up the first 1000 steps, but that the rocks that make up this massif are part of the North China Craton basement rocks formed in the Archean; some outcrops are as old as 2.75 billion years and are similar to the rocks of the so-called “greenstone belt” in other parts of the world. As such they are time related to the rocks of the Northwest of Scotland which where the subject of a talk last summer at the Stirling symposium.

Outcrop of an allgovite vein
Outcrop of an allgovite vein

At 5h15 we stopped in front of a massive basic-vein outcrop, formed by a magma intrusion in the deep crust. This 1.76 Ga old alkali basalt is composed of plagioclase and pyroxene and named allgovite; it is blackish green on the fresh surface, and lightly brown on the spherical weathered surface.

A little further on, we stopped in front of a smaller allgovite vein cutting through a quarzt diorite of the Zhongtianmen rock body, 2.5Ga old. In the book “ Igneous rocks: a classification and glossary of terms by Roger Walter” , allgovite is mentioned as an obsolete name that referred temporarily to a group of basaltic rocks that have not been classified. Still it seems that it is in use in Chinese classifications as many Chinese pages refer to it when doing a research on the net.

Taishan group inclusion
(1) the Diorite (2) Taishan group inclusion

7h and 500 steps further, we had breakfast next to an inclusion  of the Taishan group (2.55 Ga) in  the quartz diorite of the Zhongtianmen group (2.5Ga), seen before with the allgovite.

The “Taishan group” are supracrustal rocks which experienced tectono-thermal events at the end of the Neoarchean. They are the most ancient strata in China and occur as lenses and strips in granitoids before undergoing metamorphic processes, these strata formed a 12000 m thick cover of mafic to felsic volcano-sedimentary varieties, and argillo-arenaceous sediments.

Recent investigation using SHRIMP U-Pb zircon dating on metasedimetary and volcanic samples, indicate that the sediments of this group were deposited in the late Neoarchean 2.55-2.525 Ga.

The Taishan group has subsequently undergone greenschist to amphibolite facies metamorphism, in other words, moderate to high T and moderate P metamorphism, producing mainly leptites (fine-grained granulose metamorphic rocks), gneisses and amphibolites. In some of the literature it is said that the group has undergone migmatization and had formed all kinds of partial migmatites, migmatites, and migmatitic granites, which is just another way to describe metamorphic processes. Recent studies concluded that a magmatic arc model might be applied to explain the tecto-thermal evolution at the end of the Neoarchean of this group.

On our way up, we had the opportunity to see more of these rocks, as the bulk of Mount Tai is composed of intrusive magmatic bodies.

700 steps further, we had a discussion about the inscriptions on the rocks we had seen on our way up.  819 stone tablets and 1018 cliff-side inscriptions from famous scholars of different dynasties have been recorded on the mountain, some stretch back a very long way in time and display ancient characters that are no longer in use.  Chairman Mao also had some of the inscriptions carved and he also walked up the mountain. The stone masons took advantage of the large vertical-joint surfaces of the intrusive rocks to complete their work, these account for 95% of the main body of Mount Tai. The rocks are essentially tonalite, adamellite and diorite. And they were all emplaced during the Archean.

Onionskin weathering
Crouching Lion Stone

9h and 1000 steps behind us, we caught up with the participants who took the bus up to the middle station, which is where some of the initial walkers choose to get on the cable car to reach the summit. At the middle station, there was an outcrop of a beautiful onionskin weathered diorite (photo 5). This dome-shaped pattern of weathering is due to the long-term temperature difference between daytime and night. The stone’s name is the “lion stone” as, depending under the angle you look at it, you might recognise a crouching lion….

From here, the long, steep walk up to the summit started,  and we only stopped to enjoy the view and have some lunch on gneissic rocks under an ancient inscription.

steps
Ever more steep steps

From here, the long, steep walk up to the summit started,  and we only stopped to enjoy the view and have some lunch on gneissic rocks under an ancient inscription.

2 hours later we reached the top of the mountain and met up with the ones who had taken the cable car. They where sitting on a stone bench and had spent the last hour as photo models for Chinese tourists.

We stopped at several locations where  many good examples of the main rock bodies forming Mount Tai could be seen.

Inscriptions next to the summet
Inscriptions on porphyritic adamellite

The Yuhuanding rock body (2.55 Ga) is the main one that is distributed around the summit of Mount Tai, because of its hardness and strong weathering resistance. The many rock inscriptions all around the summit are carved on this rock.

It is a red coarse porphyritic adamellite, with large K-feldpath crystals in a K-feldspath, plagioclase, quartz and biotite matrix. Although the name comes from Adamello, a mountain in South Tyrol, one of the best examples in the UK is the Shap Fell granite as mentioned in the  Oxford dictionary of Earth Sciences. It is mainly located between Aolaishan adamellite (2.4-2.5 Ga), a yellowish grey medium-grained rock body, and banded gneiss of the Wangfushan formation ( 2.7- 2.75 Ga).

Day 5, 6th August, Longwan Geopark

Text and photos, Jane Hickman

view from the car park
Figure 1: view up the valley we were to explore, from the car park

This was to be our last full day of geology. We left Tai An and headed south east to Longwan Geopark in the Culaishan National Forest. Culai Mountain is said to be the sister of Mount Tai, but our visit to the area was in sharp contrast to our previous day climbing the sacred mountain: firstly we had the place practically to ourselves which was soothing to the soul after rubbing shoulders with half the population yesterday, and secondly it was raining.

the path up the stream
Figure 2: following the pâth up side the stream

When we jumped out of the minibus after an interesting run through the suburbs of Tai An and neighbouring villages we could tell that it would be a magical day no matter what the geology (figure 1). Before us heavily wooded hills were dissected by
steep twisting valleys littered with huge boulders that had fallen into the delightful stream, all softened by a light mist (figure 2). Almost like home.

Some Geology

The North China Craton comprises of three distinct blocks of which the Eastern and Western Blocks share similar geology being dominated by late Archean TTG gneiss complexes which experienced regional metamorphosed ~2.5 Ga. The Central block
contains Paleoproterozoic crustal rocks as well as some Archean material that underwent regional metamorphism ~1.85 Ga.

The North China Craton was formed by the collision of the Eastern and Western Blocks ~1.85 Ga (Zhao 2001). Imagine the simple scenario in Paleoproterozic
times where the Western Block, with a passive east margin is separated from the Eastern Block by an ocean. The western margin of the Eastern Block is active and as the ocean closes the sediments of the passive margin and the island arcs of the active margin combine to form the Central Orogenic Belt ~1.85 Ga. Globally there were a lot of these collision orogens around 2.0-1.8 Ga according to evidence from other Archean cratons around the world.

The timing of the collision remains controversial (Hou et al. 2006): was it 1.8 Ga or 2.5 Ga? However it is accepted that shortly after the formation of the craton there was widespread extension. Figure 3 shows the aulacogens of the rift together with the distribution of the associated mafic dyke swarms that have been dated 1837 ± 18Ma at Taishan (Hou et al. 2006). The swarms throughout the North China
Craton show similar dates in the range 1.84 Ga to 1.75 Ga indicating that the whole area experienced continuous extension in Late Paleoproterozoic-
Mesoproterozoic times, (Hou et al. 2008). However, the extension ceased and the triple junction failed to form.

three blocks of North China Craton
Figure 3: the three blocks of the North China Craton. Figure from Hou et al 2006

The western Shandong Province lies within the Eastern Block and comprises a granite-greenstone belt. It broadly consists of two major geological entities:
the basement gneisses and the intrusive plutonic association, (Jahn et al. 1988).

The Taishan Association (formerly known as the Taishan Group) occurs as strips and lenses within EUROPEAN GEOLOGISTS IN ASIA Field trip to China / August 1st to 10th 2011 the gneisses and granites (Figure 4). These supracrustal rocks underwent greenshist-amphibolite facies metamorphism and are considered to have
formed between 2.75 and 2.70 Ga (Wan et al. 2011).

The Taishan association is divided into three units:
a) the Yanligguan, composed mainly of amphibolite, where amygdales and lava flows have been identified and typical Archaean volcano-sedimentary associations;
b) the Shancaoyn unit, composed mainly biotite gneisses with locally preserved bedding structures and interlayered with amphibolites and mica shists;
c) the Liuhang unit which is lithologically similar to the Yanligguan unit but contains more detrital materials. Recently relic pillow lavas have been found in the Liuhang unit (Wan et al. 2011).

Simplistically the basement gneisses are amphibolite facies rocks comprising mainly of tonalite, trondhjemite and granodiorite (TTG). They are of similar metamorphic age to the Taishan association and both are thought to be derived from a depleted mantle source. The granites (or adamilites) of ~2.5 Ga on the other hand are thought to be derived from the partial melting of these older basement and supracustal rocks, (Wan et al. 2011).

Geological map of Early Precambrian
Figure 4 : a) North China Craton b) Early Precambrian of western Shandong province c) Geological map of Early Precambrian Taishan Xintai area, figure from Wan et al. 2011. (Taishan Association formarly known as Taishan Group.)

We had seen some of these rocks yesterday on our walk up Taishan. And today we were in the Taishan Group (or association) again. But I could make no sense of the rocks today - they all looked like metaigneous to me! So I ceased to worry and just enjoyed the scenery whilst the mosquitoes enjoyed me. The path criss-crossed over the stream in a succession of different types of bridges, some fixed and some
swinging. The paths were originally wood-gathers tracks but the steps were new, worked by hand from local stone and were beautiful, especially in the wet.

Sacred ceremony
In the middle of Nowhere

We stopped for lunch in a handily placed gazebo sheltering from the rain - very civilised. After lunch we continued to the end of the trail were some of us
undertook the initiation ceremony for this sacred place. On our return we met up with the warden and his herd of goats. I didn't want to get back on the bus.

Bibliography

Hou, G. et al., 2008. Geochemical constraints on the tectonic environment of the Late Paleoproterozoic mafic dyke swarms in the North China Craton. Gondwana Research, 13(1), pp.103-116.

Hou, G., Liu, Y. & Li, J., 2006. Evidence for ~1.8Ga extension of the Eastern Block of the North China Craton from SHRIMP U-Pb dating of mafic dyke swarms in Shandong Province. Journal of Asian Earth Sciences, 27(4), pp.392- 401.

Jahn, B. et al., 1988. Archean crustal evolution in China: The Taishan complex, and evidence for juvenile crustal addition from long-term depleted mantle. Precambrian
Research, 38(4), pp.381-403.

Wan, Y. et al., 2011. ~2.7Ga juvenile crust formation in the North China Craton (Taishan-Xintai area, western Shandong Province): Further evidence of an understated event from U-Pb dating and Hf isotopic composition of
zircon. Precambrian Research, 186(1-4), pp.169-180.

Zhao, G., 2001. Palaeoproterozoic assembly of the North China Craton. Geological Magazine, 138(1), pp.89- 91.

Day 6, 7th August From Tai'an to Beijin

Text Elisabeth d'Eyrames. Photos Neil Lawley.

Archean rocks
Archean rocks in Tai'an

We left Tai’an with a last stop next to a bridge where the water erosion displayed the beautiful patterns of the Archean rocks of the Taishan Complex.

Baotu Spring
Boatu Spring in Jinan

Then we started the long journey Northwards to Beijing with a stop in Jinan. It is the capital of the Shandong Province with 6 million inhabitants and it is the place where you can eat the best dumplings! We had some for lunch after having visited the Baotu Spring Park, located in the centre of the town. Seventy-two springs are listed in this area and, of course, there are many tales about Emperors, tea and springs. The Park contains several springs, amongst them the Baotu one, which is the most popular as sometimes the water gushes out when the pressure is high; Boatu means “leaping” and “jumping”. Although that day we only saw the water  gently bubbling in the middle of the pond.

The figure below, drawn by Yuan, reproduces the geological profile that was shown on a poster that explains why there are so many springs in Ji Nan.

Southwards of Jinan are the Mountains from where we came, covered with Cambrian shale that allows all the rain water to flow into the limestone formation faulted against the shale. Next to Jinan the water table hits a gabbroic pluton and thus forces the water up through the karst to the surface forming natural artesian springs.

The level of the water table is constantly monitored and displayed. That day it was at a depth of 21m. Three years ago, a shortage of rain during the summer had lowered the level of the groundwater to the extend that the Baotu Spring dried out.  The people from Jinan were asked to limit the consumption of water. What they readily did as they are very proud of their springs and care about them; many people travel from far to visit this place.

geological profile
Geological profile of the area around Jinan
Stromatolites
Stromatolites in Cambrian Limestone

In the park Jane drew our attention towards the stromatolites that could clearly be identified in limestone blocks surrounding small lakes; they display exactly the same pattern than in the Cambrian limestone in NW Scotland.

The last days in Beijin, 8th and 9th August

Text Elisabeth d'Eyrames. Photo Neil Lawley.

The Forbidden City and the Great Wall

These days were spent in Beijing visiting the very popular tourist attractions of the Great Wall and Forbidden City. Those of our party who had arrived early to see the sun rise from the Great Wall had a very quiet peaceful experience, far different to the hordes of people who visited later on.

For lunch we experienced a student meal as Chen Yuan invited us in the canteen of the Beijing University of Geosciences; 30000 students, 13 different departments, as varied as earth sciences, jewellery, environmental studies, ... .  There we also got a chance to have a look at the geological map of China which is impossible to buy in China, but is available on a British website, and meet some of her colleagues that just came back from Mongolia with bags full of samples. We didn’t have a chance to visit the lab as everyone was on vacation, but instead, we went shopping stones in a small place that belongs to the University.

During these two days, we also visited the geological museum situated close to the Forbidden City. It was a great place to go to, not only because of their  well-displayed collections, but also because of the cool and relaxing atmosphere compared to the hot Beijing summer.

The last evening was spent in a restaurant renowned for their famous Beijing Duck; as naturally, eating this animal in a formal way is compulsory when you visit Beijing for the first time.

Beijin University of Geosciences
Beijin University of Geosciences

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