Thermal structure and uplift of the Cretaceous Shimanto Belt, Kii Peninsula, Southwest Japan: An illite crystallinity and Mite bo, lattice spacing study
Thermal structure and uplift of the Cretaceous Shimanto Belt, Kii Peninsula, Southwest Japan: An illite crystallinity and Mite bo, lattice spacing study
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日本西南部纪伊半岛白垩纪四万十带的热结构和隆起：伊利石结晶度和 Mite bo、晶格间距研究
DOI：
10.1111/j.1440-1738.1996.tb00013.x
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发表时间：
1996
期刊：
影响因子：
1.5
通讯作者：
K. Imura
中科院分区：
文献类型：
--
作者：
M. Awan;K. Imura
对日本西南部纪岛白垩纪岛户带的伊利石结晶度(Ic)和伊利石b晶格间距进行了测量。在IC调查中，对该带中部和西部的103个泥质岩样品进行了分析。库布勒指数(IC)在0.28~0.71Δ°2θ之间变化，分别代表成岩变质作用和岩溶变质作用。IC分布揭示了两种截然不同的热成熟度模式。出露在构造带北部的哈纳佐诺组总体上向北倾斜，但IC值从北部的0.28Δ°2θ系统地增加到南部的0.54Δ°2θ，指示了一种倒转的热结构。其他地层的数值在该带南部的0.45~0.71Δ°2θ范围内变化很大，但从北到南没有显示出任何系统的变化，平均而言几乎保持不变。56个样品的伊利石晶格间隔值在9.006~9.041 A之间变化，对应于变质相的中压条件。这些数值与根据IC估算的古温度相结合，表明该带北部和南部地区的古地温梯度分别为22℃/公里和31℃/公里。哈纳佐诺组的热结构倒置，加上较低的古地温梯度，可能是晚白垩世相对寒冷的大洋板块俯冲的结果。较高的地温梯度可能是始新世相对较新、较热的大洋板块晚些时候俯冲造成的晚期热叠加的产物。
Abstract Illite crystallinity (IC) and illite b, lattice spacing were measured across the Cretaceous Shimanto Belt, Kii Peninsula, Southwest Japan. For the IC survey, 103 samples of argillaceous rocks were analyzed from the central area and the western area of the belt. Values of IC (Kubler Index) vary between 0.28 and 0.71 Δ°2θ and indicate diagenetic and anchizone metamorphism respectively. The IC distribution reveals two contrasting patterns of thermal maturity. The Hanazono Formation, exposed in the northern area of the belt, generally dips north, but IC values increase systematically from 0.28 Δ°2θ in the north to 0.54 Δ°2θ in the south and indicate an inverted thermal structure. Values in other formations vary widely in the southern area of the belt ranging between 0.45 and 0.71 Δ°2θ, but the values do not show any systematic change from north to south and on average remain almost constant. Illite bo, lattice spacing values for 56 samples vary between 9.006 and 9.041 A corresponding to intermediate pressure conditions of the metamorphic facies. These values, combined with paleotemperatures estimated from IC, indicate paleogeothermal gradients of 22 and 31°C/km for the northern and southern areas of the belt, respectively. The inverted thermal structure of the Hanazono Formation, together with a lower paleogeothermal gradient, possibly is a result of the subduction of a relatively cold oceanic plate during the Late Cretaceous. The higher geothermal gradient could be a product of late thermal overprinting caused by the later subduction of a comparatively younger and hotter oceanic plate during the Eocene.