Looking for the eastern margin of the Palaeo-Tethys Ocean.

The Palaeo-Tethys Ocean ran separated the continent of Gondwana from the landmasses that would become Europe and Asia during the Palaeozoic Era, opening during the Middle Cambrian and eventually closing with the formation of the Supercontinent of Pangea during the Permian/Triassic. The western part of this ocean is reasonably well understood, but the eastern extent is less well known, as much of the geology of the region has been distorted and overwritten by the Himalayan Orogeny, as the Indian Plate has impacted Eurasia from the south. The ocean probably passed along the southern margin of the South China Block (also known as the Yangtze Plate) (i.e. the southeastern coast of China), producing an area of rifting similar to that seen beneath the Red Sea today, but there is little evidence to support this.

In a paper published in the journal Acta Geologica Sinica on 27 February 2018, Hu Lisha, of the Collage of Marine Geosciences at the Ocean University of China, and the Laboratory for Marine Geology at the Qingdao National Laboratory for Marine Science and Technology, Du Yuansheng of the State Key Laboratory of Biogeology and Environmental Geology at the China University of Geosciences, and Xu Yajun, Wang Zhiwan, and Wang Chenghao, also of the Collage of Marine Geosciences  at the Ocean University of China, describe the discovery of a volcanic tuff (ash) layer from Banchen in the Qinzhou area of the Guangxi Zhuang Autonomous Region of southeastern China, could provide evidence for subduction along the southern margin of the South China Block during the Palaeozoic.

Hu et al. report the discovery of a green tuff layer between layers of Devonian siliceous rocks, from which zircons were extracted for uranium/lead dating. Zircon is a mineral formed by the crystallisation of cooling magmas. When it forms it often contains trace amounts of uranium, which decays into (amongst other things) lead at a known rate. Since lead (which has a much lower precipitation temperature) will not have been present in the original lava, it is possible to calculate the age of a zircon crystal from the ratio between these elements.

(a) Tectonic framework of the East Asia; (b) Simplified geological map of the Qinfang Trough and location of the study area; (c) Photo for the Late Devonian chert and tuff; (d) Concordia diagram and cathodoluminescence (CL) images of representative zircons for the tuff sample. Hu et al. (2018).

Eighteen zircons were subjected to this analysis. Seven of them produced ages older than 600 million years, whereas eleven produced ages of between 380 and 350 million years, consistent with a Devonian or Carboniferous age for the tuff layer. The presence of much older zircons in the sample does not undermine this, as zircons are extremely tough, and are known to be able to endure repeated cycles of subduction and volcanic eruption, nor is the broad spread of ages found in the Palaeozoic zircons, as ash deposits often contain mineral grains aggregated over a long period before being erupted.

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Earthquake in Anhui Province, China, kills at least two.

Two people are known to have died and at least twelve more have been injured following an Earthquake close to the city of Fuyang in Anhui Province slightly before 2.15 pm local time (slightly before 6.15 am GMT) on Saturday 14 March 2015, which was recorded by the China Earthquake Networks Center as having a Magnitude of 4.3 . The two casualties have been named as a man aged 75 and a woman aged 64, both of whom died in hospital after receiving head injuries during the event. though neither has been named at this time. Around 10 000 homes are reported to have been damaged by the event, with 55 having been completely destroyed.

Damage following the 14 March 2015 Anhui Earthquake. Earthquake Report/China News.

Earthquakes are common in west and southwest China, where the Eurasian Plate is being compressed by the impact of the Indian Plate from the south, but much less common in the east of the country. However southeastern China is in fact dominated by a series of tectonic blocks, annealed onto the Eurasian Plate during the Triassic.  Anhui Province lies on the boundary between the two largest of these, North and South China Blocks (the later being sometimes known as the Yangtze Plate). These blocks are being pushed to the southeast by the impact of the Indian Plate into Eurasia, leading to movement along the fault zone that separates them, resulting in occasional Earthquakes.

Tectonic map of Asia, showing relationships between the India–Asia collision, escape of Indonesian and South China blocks seaward, and extension from Siberia to the Pacific margin. (Note also the opening of back-arc basins including the Sea of Japan and the South China Sea, and extension in the Bohai Basin and eastern part of the NCC.) The North China Craton is also strongly influenced by Pacific and palaeo-Pacific subduction, perhaps also inducing extension in the eastern NCC. The palaeo Pacific and Pacific subduction zones developed in the Mesozoic, and also contributed to the hydration of the subcontinental lithospheric mantle beneath the NCC. Kusky et al. (2007). 

The approximate location of the 14 March 2015 Anhui Province Earthquake. Google Maps.

See also...

Two Earthquakes in Jilin Province, northeast China.
The United States Geological Survey recorded a Magnitude 5.4 Earthquake at a depth of 10.9 km, roughly 75 km southwest of the city of Songyuan, in...

Magnitude 4.1 Earthquake in Fujian Province, south China.
The United States Geological Survey recorded a Magnitude 4.1 Earthquake at a depth of 13.3 km, 30 km to the west of Putian City in Fujian Province...


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Earthquake in the Babuyan Islands of the Northern Philippines.

Slightly after thirty-five minutes past midnight on Sunday 15 January 2011 local time (slightly after 4.35 pm on Saturday 14 January, GMT) an Earthquake with a magnitude of 5.7 on the Richter Scale struck in the Babuyan Islands of the Northern Philippines, at a depth of about 22.4 km, according to the United States Geological Survey. There are no reports of any casualties or serious damage, nor has a tsunami warning been issued.

Map showing the location of the quake, from the United States Geological Survey.

The Babuyen Islands are part of the Luzon Volcanic Arc, a chain of volcanic islands running between Luzon in the Philippines to the south and Taiwan to the north. The arc lies on the western fringe of the Philippine Sea Plate, on the boundary with the Yangtze Plate, which is being subducted beneath it. As the subducting plate sinks into the Earth's interior, it is heated by the planet's internal heat and partially melts. Some of the melted rocks then rise through the overlying Philippine Sea Plate, forming the volcanoes of the Luzon Arc.

Diagrammatic representation of a volcanic island arc on a subductive margin.

There are five major islands in the Babuyans; Babuyan, Calayan, Camiguin, Dalupiri and Fuga.

Babuyan Island is dominated by Smith Volcano, a 688 m stratovolcano (cone-shaped volcano made up of layers of ash and lava) that last erupted in 1924.

Smith Volcano, on Babuyan Island.

Calayan Island is home to Babuyan Claro, an 843 m complex-stratovolcano (a stratovolcano with a structure more complicated than a simple cone) with a hot spring system on its southern flank, and four separate summit cones, Mount Cayonan, Mount Naydi, Mount Dionisio and Mount Pangasun. The last eruption on Babuyan Claro was in 1917, but an Earthquake on the island lead to emergency seismic monitoring in 1993, and a smoke cloud was reported over the summit in 2008.

Babuyan Claro, on Calayan Island.

There are seven volcanoes on Camiguin Island; Timpoong, Mambajao, Tres Marias, Guinsiliban Peak, Vulcan, Uhay and Hibok-Hibok. Of these only Hibok-Hibok is still active; its last major eruptive episode was in 1948-52, when more than 3000 people died and over half the population of the island emigrated.

Hibok-Hibok on Camiguin Island.

Dalupiri and Fuga lack volcanoes of note, but a new island, Didicas, emerged from the sea after a volcanic eruption in 1952. Mount Didicas now stands 288 m above the sea.

The new volcanic island of Didicas.

See also Manila shaken by mild Earthquake and Earthquakes on Sciency Thoughts YouTube.