砂岩の化学組成と堆積造構場,とくに非調和元素に関して : その1.丹波帯・超丹波帯・舞鶴帯の砂岩を例として  [in Japanese] Chemical composition and sedimentary tectonic setting of sandstones with special reference to in compatible elements : Part 1. a case study of the sandstones from the Tamba Belt, Ultra-Tamba Zone and Maizuru Belt  [in Japanese]

ペルム紀からジュラ紀にわたる年代の丹波帯, 超丹波帯, 舞鶴帯の砂岩について地球化学的分析を行った。主要化学組成による識別図ではこれらの砂岩は受動的大陸縁から陸弧の領域にプロットされる。丹波帯砂岩の化学組成の変化は後背地の侵食過程に基づいており, 舞鶴帯砂岩の変化は造構場の時代的変遷に基づいている。超丹波帯味間層の低いアルカリ比, K/Cs比およびRb/Cs比は陸弧の分化した火山岩に由来したものであろう。希土類元素の分布パターンは源岩の特徴を反映しており, また風化や成熟過程の度合を示している。HFS元素については, ZrやHfは主に堆積成熟過程を反映して増加し, いっぽうNbやTaは通常, 堆積過程や風化によって減少する。丹波帯の砕屑岩のORG(仮想的海嶺花崗岩)規格化パターンは活動的大陸縁の花崗岩のものに良く似ている。同様のパターンから, 超丹波帯の味間層や舞鶴帯の舞鶴層群の砂岩は陸弧に由来するとみなせる。

Sandstones from the Tamba Belt, Ultra-Tamba Zone and Maizuru Belt, ranging from Permian to Jurassic in age, are analyzed geochemically. On major element discrimination diagrams, they plot in the areas from passive continental margin to continental island arc settings. The chemical change of the sandstones from the Tamba Belt is a result of erosional process in the source area, while the change of those from the Maizuru Belt is a result of periodical change in the tectonic setting. Low alkaline ratios, K/Cs and Rb/Cs in the Ajima sandstones from the Ultra-Tamba Zone indicate that clastics have been derived from enriched volcanic rocks of a continental island arc. The distribution pattern of rare earth elements reflects the characteristics of the source rocks and also shows the degree of weathering and maturing process. As to HFS elements, of which depletion in igneous rocks indicates are volcanism, the values of Zr and Hf mainly reflect sedimentary maturing processes. On the other hand, Nb and Ta usually decrease during sedimentary and weathering processes. ORG ("oceanic ridge granite") normalized distribution patterns of clastic rocks from the Tamba Belt closely resemble those of granite from active continental margins. Owing to those patterns, both Ajima sandstones of the Ultra-Tamba Zone and Maizuru sandstones of the Maizuru Belt are regarded as being derived from a continental island arc.