Graptolites and the Guangxian Orogeny, China
Tuesday, December 7, 2010 9:01:47 PM
Apart from a reassessment of Upper Ordovician graptolites in China a recent study also recommend the studied graptolites to assess the initiation time of a tectonic event known as the Kwangsian Orogeny (orogeny = mountain building period). Well, known or known. I must admit that i have a few problems with Chinese orogenies, and tectonic plates, and (not least) their names.
The studied Ordovician graptolites (Ordovician - ca. 488-444 million years ago) were from southern Guangxi, and this region has lent its name to the Guangxian Orogeny (a synonym for the Kwangsian Orogeny, just spelt differently, transcription from Chinese to Latin characters is not straightforward). The Guangxian Orogeny was earlier seen as part of the Caledonian Orogeny (ca. 490-390 million years ago In Northern Europe and North American), because it took place in a similar time-span. Changes in water depths an depositional rates in the Period from 475-450 million years ago may indicate that the Guangxian Orogeny started in the early Katian (Katian - ca. 456-446 million years ago).
The Guangxian Orogeny would have been a result of the convergence and collision between the Cathaysian and Yangtze blocks. Now here is another confusing problem as these terms have been used differently in the literature in the past. The same is true for Yangtze Plate/Block and South China Plate/Block. For instance the terms ‘Yangtze Plate’ and ‘South China Plate’ have both been used for the modern plate shown on the following map. Yangtze Plate is the term used in ‘An updated digital model of plate boundaries’ by Peter Bird (2003).
An older discussion (from 2000) on the orogeny, we are talking about, is found in ‘Reinterpretation of the Guanxian Orogeny’ by Haoruo. This paper placed the Guanxian Orogeny at the end of Silurian ca. 460 million years ago.
Relevant full-text pdf-files:
Ordovician graptolite-bearing strata in southern Jiangxi with a special reference to the Kwangsian Orogeny
Reinterpretation of the Guangxian Orogeny
Pre-Devonian tectonic evolution of the eastern South China Block: Geochronological evidence from detrital zircons
An updated digital model of plate boundaries