Notice on the World Earth Day Activities of Tianzhushan UGGp
06/08/2021

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Tourmaline-bearing Ultrahigh Pressure Eclogites Are Found in Tianzhushan UGGp
Pubdate:5/6/2020 WednesdayCategory:Geopark News

In 2019, Dr. Guo Shun, from Institute of Geology and Geophysics, Chinese Academy of Sciences, published an article on the famous international periodical Geochimica et Cosmochimica ActaGCA, in which tourmaline-bearing ultrahigh pressure eclogites were reported to be found in Hanchangchong (Shuanghe) - Baiyangling area within Tianzhushan UGGp. This is the first case of tourmaline-bearing eclogite to be found in the largest ultrahigh pressure metamorphic belt in the world --- Dabieshan Ultrahigh Pressure Metamorphic Belt, and this is also the first discovery of tourmaline-bearing eclogite exposed in marble throughout the world.

Tourmaline, one of the most important hosts of boron in crustal rocks, has rarely been found in natural high-pressure and ultrahigh pressure eclogites. The first finding of tourmaline-bearing UHP ecologites and veins in the Dabie terrane occur exclusively in impure UHP marbles. Investigations on the eclogite-vein-marble system provide important insights into the origin, flow, and metasomatic effects of eclogite-facies, B-rich fluids in continental subduction zones. Petrologic and geochemical evidence indicates that tourmaline in the eclogites formed by metasomatism due to the infiltration of a B-rich fluid under conditions of ca. 2.2-2.6 GPa and 610-6600 C. The HP veins, containing euhedral tourmaline and occurring at the eclogite-marble contacts or in the interiors of eclogite lenses, represents the crystallized products of the infiltrating fluid. Systematic compositional variations along the profile from the interiors of the eclogite lense to their margins and mass-balance calculations indicate large inputs of B, carbon, large ion lithophile elements and light rare earth elements to the eclogites during fluid infiltration. This is a newly-added rock type of UHP metamorphic rocks found within Tianzhushan UGGp.

Tianzhushan UGGp is an important area for the research of typical UHP metamorphic belt and continental subduction zone of China, and many domestic and foreign scholars have made fruitful researches. In last century, coesite and diamond were successively found in eclogites in Bixiling area and Xindian area within Tianzhushan UGGp, which were respectively the third case in the world and the second case to be found in metamorphic rocks.

Numerous ultrahigh pressure metamorphic rocks, such as coesite-bearing eclogite, diamond-bearing eclogite, jadeite quartzite, garnet peridotite, gneiss, marble, metamorphic granite and serpentinite, have been found in Tianzhushan UGGp, which has become a treasure trove for the study of continental dynamics. In recent years, in order to protect the precious geoheritage and disseminate geosciences, Tianzhushan UGGp has held many academic symposiums and UHP field trips, cooperated with University of Science and Technology of China and Nanjing University, etc.

Paper links:

https://www.sciencedirect.com/science/article/abs/pii/S0016703719301516

 

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