博物館報告
名古屋大学博物館報告 第36号
- 目次 PDF (165 KB)
- 束田 和弘（TSUKADA Kazuhiro）
名古屋大学博物館のSEM-EDXによる含水鉱物化学組成の定量分析
Quantitative analysis of chemical composition of hydrous silicate minerals using SEM-EDX installed at Nagoya University Museum
vol.36, p.1-9. PDF (446.5 KB)
DOI: 10.18999/bulnum.036.01走査型電子顕微鏡（SEM）に搭載されたエネルギー分散型X線分光器（EDX）による定量分析が実用化され，微小領域分析の様々な分野で活用されている．地学分野では，造岩鉱物や火山ガラスなどの定量分析について様々な事例研究が報告され，主成分元素に関しては電子線マイクロアナライザー（EPMA）と遜色ない精度で定量が可能となっている（木村，1994；佐野，2003；川野ほか，2010；大場ほか，2011；小暮ほか，2014；束田，2018 など）．
電子線照射によるX線定量分析では，測定値はプローブ電流の変化とともに増減するが，各元素濃度の相対比はほぼ一定である．したがって名古屋大学博物館設置のSEM-EDXでは，測定値の合計を100%規格化することによって無水鉱物の主成分元素濃を見積もっている（束田，2018）．しかしこの方法では，EDXで検出できないH2Oを主成分として含む鉱物（以下，含水鉱物）の定量分析はできない．一方，地学分野では，火成・変成作用における温度・圧力条件の推定などの際に，含水鉱物の化学組成が重要となることがある．含水鉱物の化学組成を見積もるためには，「H2O以外の各主成分元素の濃度」を正確に求める必要がある．言い換えると，スタンダード登録時と未知試料測定時のプローブ電流を同一にして，各主成分元素の濃度を正確に測定する必要がある．しかしながら，名古屋大学博物館のSEMは“プローブ設定”機能によってプローブ電流を相対的に増減させることは可能であるが，プローブ電流値そのものを制御することはできない．そこで今回，SEMに微小電流計を接続し，プローブ電流の制御と含水鉱物の定量分析を試みたのでここに報告する． - 須賀 永帰（SUGA Eiki）
長野県木曽町（旧開田村）管沢遺跡出土資料の報告
Report of Archaeological Remains from Kudasawa site, Kiso Town, Nagano Prefecture
vol.36, p.11-34. PDF (4.3 MB)
DOI: 10.18999/bulnum.036.02Kudasawa archaeological site is located in Kiso town (former Kaida village) of Nagano prefecture, Japan, and is known for the discovery of Jomon pottery of the Ario type that belongs to the middle phase of the Early Jomon period. In 1961, the site was excavated by the Department of Archaeology of Nagoya University, and the summary description was preliminary reported in 1966, though a full list of the discovery is yet to be reported. Here we report detailed lists of the archaeological assemblages of the excavation in 1966, especially focusing on chipped stone artifacts.
The comparison of lithic assemblages between Kudasawa site and nearby Jomon sites indicate that arrowheads of Kudasawa site are characterized by the use of diverse stone raw materials including chert as the most common raw material type, followed by obsidian, rhyolite, and chalcedony. Future studies for the identification of these raw material sources are necessary to clarify lithic resource exploitation strategies by Jomon foragers in this region.管沢（くださわ）遺跡は長野県木曽町（旧開田村）に所在する縄文時代の遺跡で，出土した有尾式の縄文土器から前期中葉の遺跡とされている．1961 年に名古屋大学考古学研究室によって発掘調査が行われ，その成果は1966 年に報告された．しかしながら，報告は概要が示されただけで，総合的な資料報告には至らなかった．そこで本論では1961年の調査時に出土した遺物を，特に石器に重点を置いて報告する．
整理した管沢遺跡の資料と周辺の遺跡とを比較してみると，管沢遺跡の石鏃の石材は多様で，特にチャート製の割合が高い．他にも下呂石製や黒曜石製，玉髄製の石鏃も出土しており，これらの石材の産地を同定することで，当時の縄文人の資源に対する多様な行動を明らかにできることが期待される． - Bayart NADMID, Kazuhiro TSUKADA, and Makoto TAKEUCHI
Geochemistry of the basaltic blocks in the Jurassic and Cretaceous accretionary complexes in the Yoshino area, central Kii Peninsula, Southwest Japan
vol.36, p.35-51. PDF (6.4 MB)
DOI: 10.18999/bulnum.036.03This study describes the geochemistry of basaltic blocks in the Daifugendake and Wasabidani complexes (Chichibu belt) and the Unokawa and Takaharagawa complexes (Shimanto belt) exposed in the Yoshino area of the central Kii Peninsula of Japan and discusses the tectonic implications. In this study, we examined 5 samples from the Chichibu belt and 10 samples from the Shimanto belt. The samples are divided into alkaline and tholeiitic basalts. Blocks in the Chichibu belt and the Takaharagawa complex of the Shimanto belt are determined to be alkaline basalts, and those in the Unokawa complex of the Shimanto belt are tholeiitic basalts. Alkaline and tholeiitic basalts have been recovered from the Chichibu and Shimanto belts throughout southwest Japan, respectively. Alkaline basalts in the Takaharagawa complex, which have never been described in the Shimanto belt, may imply that Chichibu belt components are involved into the Shimanto belt in the Yoshino area. It is possible that alkaline basalt derived from the Chichibu belt was mixed into a “shear zone” (the mélange unit) formed through thrust movement following accretion.
- TSUKADA Kazuhiro, SHIMURA Yusuke, and NADMID Bayart
The magmatic relationship between the "Kurotani ultra-mafic rock" and the Ordovician(?) Iwatsubodani Formation, Takayama City, Hida Gaien belt, central Japan: the chemical composition of clinopyroxene
vol.36, p.53-68. PDF (6.8 MB)
DOI: 10.18999/bulnum.036.04A major problem for understanding the tectonic history of the Inner zone of Southwest Japan is the spatial tectonic contrast between the rocks in its western and eastern parts. In the western part of the zone, the Sangun–Renge, Akiyoshi, Maizuru, and Ultra-Tanba belts are widely exposed, whereas they are fragmented in a narrow area along the Hida Gaien belt in the eastern part. The Hida Gaien belt with its fault-bound blocks is thus a key unit for understanding the geology. The lithostratigraphy and structure of the blocks composed of volcanic/sedimentary rocks have been studied previously (e.g., Tsukada et al., 2004), but few attempts have been made to study the blocks of ultra-mafic rock which are critical to understanding the tectonic process in the Hida Gaien belt. In the Nakao area, Takayama City, Ordovician(?) mafic volcanic rocks (the Iwatsubodani Formation) of the Hida Gaien belt have been thrust onto an unclassified block of Kurotani ultramafic rock (KUM). This paper describes the mineral chemical composition of rocks from the KUM and the Iwatsubodani Formation and discusses the magmatic relationship between their clinopyroxene (Cpx) chemical composition.
The Mg# (= Mg/(Mg + Fe) mol%) of Cpx in the KUM is 0.93–0.98. In the Iwatsubodani Formation, sub-ophitic lava (Mg# of interstitial Cpx = 0.41–0.79) is overlain by pyroclastic rock with abundant clasts of porphyritic lava (Mg# of Cpx porphyry = 0.75–0.90). In the variation diagram, most elements of Cpx from the KUM and Iwatsubodani Formation form a linear trend against Mg#. Thus, the KUM and Iwatsubodani Formation probably both originated through fractionation from a single magma source. Although the porphyritic lava overlies sub-ophitic lava in the Formation, the Mg# of Cpx in the porphyritic lava is much higher than that of the underlying sub-ophitic lava. This fact suggests that the Cpx porphyry of the porphyritic lava had probably crystalized in a magma chamber before the sub-ophitic lava stage.