Apatite is one of the accessory minerals in the UHP metamorphosed eclogites at Northern Dulan belt, North Qaidam. It appears in three kinds of occurrences: (1) included in garnet which often shows cracks along the apatite grains, (2) coexisting with omphacite, rutile and/or clinozoisite in matrix and often surrounded by garnet, and (3) coexisting with retrograded minerals. The three eclogite samples examined in the present study are enriched in garnet. Two of them contain up to 80 vol.% garnet and the other is a porphyry of medium-grained garnet. They commonly show cracks and features of retrograde metamorphism, such as fissure-filling of secondary minerals including calcite or greenschist facies minerals. There are two size-ranges of well-oriented sulfide minerals included in apatite. One is nanometer-sized sulfide needles (50 ¡Ñ 20 ~ 870 ¡Ñ 120 nm) and particles (55 ~ 370 nm). The other is micrometer-sized sulfide needles (~20 ¡Ñ 0.5 £gm) and rods (~2.5 ¡Ñ 0.5£gm). Fluid inclusions and the micrometer-sized sulfide minerals commonly occur in the apatite grains that are near the cracks. Both nanometer- and micrometer-sized sulfide minerals are elongated with their long axes being normal or parallel to the c axis of the apatite. We used SEM-EDS and TEM-EDS to analyze and found that the sulfide minerals are troilite, pyrrhotite, Cu-bearing pyrrhotite and chalcopyrite. There are two sets of preferred crystallographic orientations for the dominated troilite and host apatite. The rod troilite is elongated along its a axis and <001>troilite // <001>apatite, <48-3>troilite ∡ <13-3>apatite = ~ 0.6º, (2-10)troilite // (3-10)apatite, <100>troilite ∡ <100>apatite = ~ 10º. The needle troilite is also elongated along its a axis and <001>troilite ¡æ <001>apatite, <-110>troilite ∡ <-12-2>apatite = ~ 1.3º, (11-2)troilite // (0-1-1)apatite. The preferred crystallographic orientation relationships, in terms of the c axis of troilite being parallel or normal to the c axis of host apatite, are similar to those for oriented quartz precipitates and omphacite hosts in the previous studies. According to the observations that only few sulfide minerals included in other minerals, the occurrences of apatites, and the microtextures of sulfide minerals, we suggest that the origin of sulfide minerals may relate to metasomatism during plate subduction. Metal ions such as iron, copper, cobalt and nickel were carried by chlorine- and sulfur-enriched fluids, which might be trapped as primary fluid inclusions in the apatite. The sulfide minerals then formed at the sites of fluid inclusions with the aid of fluids and available ions.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0911112-161223 |
| Date | 11 September 2012 |
| Creators | Wang, Yi-Liang |
| Contributors | Huai-Jen Yang, Yen-Hong Shau, Wei-Teh Jiang |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | Cholon |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0911112-161223 |
| Rights | user_define, Copyright information available at source archive |
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