The Kamuikotan zone in Hokkaido, Japan: tectonic mixing of high-pressure and low-pressure metamorphic rocks
The Kamuikotan zone in Hokkaido, Japan: tectonic mixing of high-pressure and low-pressure metamorphic rocks
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日本北海道神居古丹地区：高压和低压变质岩的构造混合
DOI：
10.1111/j.1525-1314.1983.tb00275.x
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发表时间：
1983
影响因子：
3.4
通讯作者：
S. Banno
中科院分区：
文献类型：
--
作者：
H. Ishizuka;M. Imaizumi;Nobuo Gouchi;S. Banno
。在日本北海道中部的Kamuikotan带，两种不同类型的变质岩在构造上混合在一起，并伴随着大量的超镁铁质岩石，一种类型由高压变质岩组成，另一种类型由低压变质岩组成。高压变质岩可分为两类。(1)来自泥岩、砂岩、石灰岩、各种基性岩如枕状和块状熔岩、透明碎屑岩和凝灰岩、放射虫(瓦朗期至豪特里亚)硅质岩的进积绿片岩至蓝闪片岩相岩石，其中基性岩和硅质岩，偶尔还有砂岩，以泥岩包裹的不连贯块体(或包裹体)赋存。(2)有少量变质角闪岩和蓝闪方解石的逆行角闪岩，它们是包裹在前进型泥岩或蛇纹岩中的构造(或外来)块体，或由断层与这些前进型岩石隔开。前进型变质岩的K-Ar年龄(斑状白云母为72 Ma、107 Ma和116 Ma)比退变质岩(白云母为109 Ma、132 Ma、135 Ma和145 Ma，角闪岩为120 Ma)要年轻。低压变质岩由蛇绿岩系镁铁质岩系组成，其顶端为放射虫(泰托纪)硅质岩，变质程度从沸石相到绿片岩(部分为阳起石-钙质斜长岩)相至角闪岩(部分为角闪石-麻粒岩)相。这种低压变质作用与“洋底”变质作用有许多相似之处。并结合中生代板块运动讨论了这种混杂带的构造演化。
. In the Kamuikotan zone, central Hokkaido, Japan, two distinct types of metamorphic rocks are tectonically mixed up, along with a great quantity of ultramafic rocks; one type consists of high-pressure metamorphic rocks, and the other of low-pressure ones. The high-pressure metamorphic rocks are divided into two categories. (1) Prograde greenschist to glaucophaneschist facies rocks derived from mudstone, sandstone, limestone, a variety of basic rocks such as pillow and massive lavas, hyaloclastite and tuff, and radiolarian (Valanginian to Hauterivian) chert, among which the basic rocks and the chert, and occasionally the sandstone, occur as incoherent blocks (or inclusions) enveloped by mudstone. (2) Retrograde amphibolites with minor metachert and glaucophane-calcite rock, which are tectonic (or exotic) blocks enclosed within prograde mudstone or serpentinite, or separated from these prograde rocks by faults. The K-Ar ages of the prograde metamorphic rocks (72, 107 and 116 Ma on phengitic muscovites) are younger than those of the retrograde rocks (109, 132, 135 and 145 Ma on muscovites, and 120 Ma on hornblende). The low-pressure metamorphic rocks consist of the mafic members of an ophiolite sequence with a capping of radiolarian (Tithonian) chert with the metamorphic grade ranging from the zeolite facies, through the greenschist (partly, actinolite-calcic plagioclase) facies to the amphibolite (partly, hornblende-granulite) facies. The low-pressure metamorphism has a number of similarities with that described for‘ocean-floor’metamorphism. The tectonic evolution of such a mixed-up zone is discussed in relation to Mesozoic plate motion.