Komatiitic and tholeiitic metavolcanics of the Siivikkovaara area in the Archean Kuhmo greenstone belt, eastern Finland
Komatiitic and tholeiitic metavolcanics of the Siivikkovaara area in the Archean Kuhmo greenstone belt, eastern Finland
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芬兰东部太古代库赫莫绿岩带 Siivikkovaara 地区的科马提质和拉斑玄武岩变质火山岩
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发表时间：
1980
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通讯作者：
E. Hanski
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作者：
E. Hanski
HANSKI， EERO 1980：芬兰东部太古代Kuhmo绿岩带Si ivikkovaara地区的岩石和玄武岩变质火山。公牛。青烟。Soc。芬兰52,67 - 100。位于太古宙中段绿岩带的Siiv ikkovaara地区，科马提岩浆岩变质火山丰富且保存完好。与下面的拉斑岩一起，这些组成Kellojärvi组，分为两个组，Pahakangas组和Si ivikkovaara组。P - h - k - a - g - s构造由枕状和块状火山岩和嵌套带状铁构造组成。变质熔岩为太古宙典型的低钾拉斑岩。上面的Si ivikkovaara格式有三个亚单位，Siivikko， Mäkinen和Raivio成员。Siivikko段变质火山岩主要为橄榄岩型小岩（MgO ^ 18°/o），具有角砾岩、枕状、棘状织构和多角形节理等典型岩石构造。微旋结构岩石中镁含量最高，MgO含量约为20°/o。Mäkinen段由玄武岩和辉石岩组成（MgO < 18°/o），以变型枕状熔岩的形式出现。Raivio成员由所有与数学元集合相关的元素组成。Si ivikkovaara地区的棘状结构最初是由斜辉石形成的。岩浆流中可划分出Ai、a -z、Bi和BL带，Ao为树枝状、板状或针状角闪石伪晶为主的亚基，并有较强的辉石质。推导出螺旋变形流的液体成分在辉石科玛蒂范围内。这些流动主要由橄榄石和少量辉石和铬铁矿沉淀组成。钠长石是由海水引起的钠交代作用形成的。有许多指标支持Kellojärvi群熔岩起源于深海的观点。尽管Si ivikkovaara格式的komati tes中MgO含量相对较低，但在该格式中发现了两个镍铜矿床。
HANSKI, EERO 1980: Komati i t ic and tholeiitic metavolcanics of the Si ivikkovaara area in the Archean Kuhmo greenstone belt, eas tern Finland. Bull. Geol. Soc. Finland 52, 67—100. Komatii t ic metavolcanics are abundan t and wel l -preserved in the Siiv ikkovaara area, which lies in the middle par t of the Archean K u h mo greenstone belt. Together wi th the under lying tholeiites, these fo rm the Kellojärvi Group, which is divided into two formations, those of Pahakangas and Si ivikkovaara . The P a h a k a n g a s Format ion consists of pillowed and massive me ta lavas and intercalated banded iron formations. The meta lavas are chemically typical Archean low-potassium tholeiites. The overlying Si ivikkovaara Format ion has three subunits , the Siivikko, Mäkinen and Raivio Members . The metavolcanics of the Siivikko Member, which are mainly peridotit ic komati i tes (MgO ^ 18 °/o), have many s t ruc tures typical of ext rus ive rocks, including breccias, pillows, spinifex textures and polygonal jointing. The microspin i fextextured rocks r ichest in magnes ium contain about 20 °/o MgO. The Mäkinen Member consists of basaltic and pyroxeni t ic komati i tes (MgO < 18 °/o), which occur in the fo rm of variolitic pillow lavas. The Raivio Member is composed of u l t r amaf ic to mafic meta tuf f s . The spinifex tex tures in the Si ivikkovaara area were originally formed by clinopyroxene. Zones Ai, A-z, Bi and BL> can be dis t inguished in the sp in i fextex tured lava flows, and Ao has f u r t h e r subuni ts dominated by dendritic, platy or acicular hornblende pseudomorphs a f te r cl inopyroxene. The liquid composition of the spini fextex tured f lows is deduced to be in the range of pyroxenit ic komatii te. These f lows are d i f ferent ia ted mainly by olivine and minor pyroxene and chromite precipitat ion. Albite in the sp in i fextex tured rocks is formed through sodium metasomat ism caused by sea-water . There are m a n y indicators to support the notion of a deep-sea origin for the lavas of the Kellojärvi Group. Despite the relat ively low MgO content of the komati i tes in the Si ivikkovaara Format ion, two nickel-copper occurences have been found in the format ion.