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

根据沸石转化的概念，研究了日本西南部九州和本州西部第三系碎屑岩的成岩成熟度。凝灰质沉积物中的沸石起源于火山玻璃，由斜发沸石和丝光沸石转变为钠长石，通过方沸石和方沸石，以及浊沸石和方沸石的变质过程，X-射线衍射仪确定矿物为斜发沸石、方沸石、方沸石和浊沸石。研究区第三系岩石主要属于斜发沸石-丝光沸石带和方沸石-方解石带，分别对应于Shimyama和Iijima(1977)的第II和IIIa沸石带。第三系层序的最低部分位于钠长石或浊沸石-方沸石-方沸石带中，个别地区层序的最低部分：Amakusa和Takashima，各地区层序的垂直沸石分带指示埋藏成岩成因。这种矿物分带与煤级变化，即有机变质程度的变化有很好的协调性。上述两种组合方法对层序的检测表明，成岩作用程度在平面上发生了变化。西南部地区的学位高于北部地区，而北部地区的学位则向北推进。这种成熟度的区域变化表明，控制成岩作用的地质条件、古地温梯度、火成岩活动、盖层厚度等随盆地的不同而不同。九州地热区的沸石显示出与已描述地区不同的产状和矿物学性质。这些差异应该在今后的研究中进行详细的研究。

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.