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Microdiamonds, their classification and tectonic implications for the host eclogites from the Dabie and Su-Lu regions in central eastern China

Published online by Cambridge University Press:  05 July 2018

Shutong Xu*
Affiliation:
Anhui Institute of Geology, 19 Ningguo Road, Hefei, 230001, China Laboratory of Continental Dynamics of Ministry of Land and Resources of China, Beijing, 100037, China
Yican Liu
Affiliation:
Anhui Institute of Geology, 19 Ningguo Road, Hefei, 230001, China China University of Sciences and Technology, Hefei, 230026, China
Guanbao Chen
Affiliation:
Anhui Institute of Geology, 19 Ningguo Road, Hefei, 230001, China
Shouyuan Ji
Affiliation:
Department of Earth Sciences, Nanjing University, Hankou Road, Nanjing, 210008, China
Pei Ni
Affiliation:
Department of Earth Sciences, Nanjing University, Hankou Road, Nanjing, 210008, China
Wanshen Xiao
Affiliation:
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China
*

Abstract

We have found >10 in situ microdiamonds in thin sections of eclogites from the Dabie and Su-Lu regions of central eastern China since the first occurrence of microdiamond in eclogites from the Dabie Mountains (DMT) reported in 1992. The microdiamonds are found not only in the central part but also in the northern part of the DMT. Several free crystals have been recovered from the crushed eclogites from the central DMT. Most in situ microdiamonds are inclusions in garnets but a few larger ones are intergranular. Most of the diamondiferous eclogites in the central part of the DMT are associated with coesite. Most importantly, the observation of microdiamonds in northern Dabie lead us to question the supposition that this is a low-P metamorphic terrane. All the diamondiferous eclogites from both the north and central DMT are of continental affinity as demonstrated by their negative εNd values. Therefore, both the north and central eclogite belts in the DMT are considered to be from the deep subducted terrane. Five in situ microdiamonds and two free crystals are first reported in this paper. The dimensions of the in situ microdiamonds are 30–180 µm and the free crystals are up to 400–700 mm across. All the microdiamonds are confirmed as such by Raman spectroscopy. The results of an infrared spectroscopic investigation on two larger free crystals and two in situ microdiamonds show that all the microdiamonds from both the Dabie and Su-Lu regions are mixed types IaA and IaB diamonds and there is no indication of any synthetic microdiamonds in our samples because such synthetic microdiamonds are always rich in type Ib.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2005

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