Zeolitic diagenesis of the Tertiary formations in the Inner zone of Southwest Japan

本文主要根据沸石转化的概念，对日本西南部内带、九州和本州西部第三纪碎屑岩的成岩成熟度进行了研究。火山玻璃质凝灰质沉积物中的沸石在退变质作用过程中由斜发沸石、丝光沸石经片沸石、方沸石、浊沸石、方沸石转变为钠长石，X射线衍射鉴定为斜发沸石、片沸石、方沸石和浊沸石。研究区第三系岩石主要为斜发沸石-丝光沸石带和片沸石-方沸石带，分别对应于Shimoyama和Iijima（1977）的沸石带II和IIIa。第三系层序的最低部分在有限的地方，阿马库萨和高岛，是在钠长石或浊沸石-方沸石带。这种矿物分带与煤阶的变化，即有机变质程度的变化相协调。这两种方法结合起来对层序的研究，显示了成岩作用程度的平面变化。西南部地区的学位高于北方地区，在后者地区，他们向北推进。成熟度的这种区域性变化反映了控制成岩作用的地质条件，古地温梯度、岩浆活动、覆盖层厚度等因盆地而异。来自九州地热区的锆石显示出与已经描述过的地区不同的产状和矿物学性质。这种差异应在未来的研究中详细研究。

Diagenetic maturation of the Tertiary clastic rocks in the Inner zone of Southwest Japan; Kyushu and the western part of Honshu, was examined based mainly on a zeolite transformation concept. Zeolites in tuffaceous sediments originated from volcanic glass transform from clinoptilolite and mordenite to albite through heulandite and analcime, and laumontite and analcime in accordance with a progress of deagenesis.Minerals identified by X-ray diffraction in this study are clinoptilolite, heulandite, analcime and laumontite. The Tertiary rocks in the studied areas belong mainly to the clinoptilolite-mordenite and heulandite-analcime zones which corresponed to the zeolite zones II and IIIa by Shimoyama and Iijima (1977) respectively. The lowest parts of the Tertiary sequences in the limited places; Amakusa and Takashima, are in the albite or laumontite-analcime zones.The vertical zeolitic zoning of the sequences in each district indicates burial diagenetic origin. Such a mineral zoning is well harmonized with variation of coal rank, namely the level of organic metamorphism. The examination of the sequences by the above two combined methods shows an areal change of the degrees of diagenesis. The degrees are higher in the southwestern areas than in the northern regions, and in the latter regions they are promoted toward the north. Such areal changes of the maturation degrees show that the geologic conditions controlling the diagenesis; Paleo-geothermal gradient, igneous activity, overburden thickness, etc. were varied with each basin. Zeolites from the geothermal areas in Kyushu show a mode of occurrence and mineralogic properties different from those in the already described areas. Such differences should be researched in detail in the future studies.