number of downloads : ?
ID 2843
Title Transcription
ジンバブエクラトン ノ カコウガン シツガン ニ フクマレル ジルコン ノ ケイタイ ニ ツイテ
Title Alternative (English)
Morphological Characteristics of zircons in granitoids of the Archean Zimbabwe Craton
File
language
jpn
Author
Yamada, Satoshi
Tsunogae, Toshiaki
Description
The Zimbabwe Craton, which is a typical Archean granite-greenstone terrane, contains two different types of granitoids ; older gneiss (3500~3000 Ma) and younger granite (2900~2600 Ma). This study focused on morphological characteristics of zircons in the older gneiss and the younger granite to understand mineralogical and petrological differences between the two granitoids.
All samples examined in this study have two types of zircon. One is an elongated, fine-grained, and euhedral zircon (Type-A). The younger granite contains many Type-A zircons without any resorption texture, because the granitoid did not suffer later metamorphism and/or partial melting. The other type is a coarse-grained zircon with overgrowth texture around older core (Type-B). This type is abundant in the older gneiss. For example, sample ZC10A, which is a typical older gneiss, contains many Type-B zircons. We considered that the core of the zircons was formed during crystallization stage of the protolith of the older gneiss. The rock was then metamorphosed and/or partly molten and formed overgrowth texture. Presence of both euhedral and anhedral zircons in one specimen may imply that euhedral zircons were included in earlier-stage minerals(ex.biotite) before the last stage of metamorphism and/or melting.
The younger granite contains Type-B zircons smilar to the older gneiss, although their amomt is little. We thus regard the origin of the younger granite as a partial melting of the older granite. Some zircons of the older gneiss have thus survived during later thermal event and now present in the younger granite.
Journal Title
Memoirs of the Faculty of Education, Shimane University. Natural science
Volume
32
Start Page
15
End Page
27
ISSN
05869943
Published Date
1998-12-01
NCID
AN00107941
Publisher
島根大学教育学部
Publisher Aalternative
The Faculty of Education Shimane University
NII Type
Departmental Bulletin Paper
OAI-PMH Set
Faculty of Education
他の一覧