Veizer J, Hoefs J, Lowe D R, Thurston P C
Department of Geology, University of Ottawa, Canada.
Geochim Cosmochim Acta. 1989;53:859-71. doi: 10.1016/0016-7037(89)90031-8.
Carbonate rocks with geological attributes of marine sediments are a minor component of the Archean greenstone belts. Despite their relative scarcity, these rocks are important because they record chemical and isotopic properties of coeval oceans. The greenstones containing such carbonates appear to cluster at approximately 2.8 +/- 0.2 and approximately 3.5 +/- 0.1 Ga ago. The samples for the younger group are from the Abitibi, Yellowknife, Wabigoon (Steep Rock Lake), Michipicoten and Uchi greenstone belts of Canada and the "Upper Greenstones" of Zimbabwe. The older group includes the Swaziland Supergroup of South Africa, Warrawoona Group of Australia and the Sargur marbles of India. Mineralogically, the carbonates of the younger greenstones are mostly limestones and of the older ones, ferroan dolomites (ankerites); the latter with some affinities to hydrothermal carbonates. In mineralized areas with iron ores, the carbonate minerals are siderite +/- ankerite, irrespective of the age of the greenstones. Iron-poor dolomites represent a later phase of carbonate generation, related to post-depositional tectonic faulting. The original mineralogy of limestone sequences appears to have been an Sr-rich aragonite. The Archean carbonates yield near-mantle Sr isotopic values, with (87Sr/86Sr)o of 0.7025 +/- 0.0015 and 0.7031 +/- 0.0008 for younger and older greenstones, respectively. The best preserved samples give delta 13C of +1.5 +/- 1.5% PDB, comparable to their Phanerozoic counterparts. In contrast, the best estimate for delta 18O is -7% PDB. Archean limestones, compared to Phanerozoic examples, are enriched in 16O as well as in Mn2+ and Fe2+, and these differences are not a consequence of post-depositional alteration phenomena. The mineralogical and chemical attributes of Archean carbonates (hence sea water) are consistent with the proposition that the composition of the coeval oceans may have been buffered by a pervasive interaction with the "mantle", that is, with the oceanic crust and the coeval ubiquitous volcanosedimentary piles derived from mantle sources.
具有海洋沉积物地质属性的碳酸盐岩是太古宙绿岩带的次要组成部分。尽管它们相对稀少，但这些岩石很重要，因为它们记录了同期海洋的化学和同位素特性。含有此类碳酸盐的绿岩似乎集中在大约28亿±0.2亿年前和约35亿±0.1亿年前。较年轻组的样本来自加拿大的阿比蒂比、耶洛奈夫、瓦比贡（陡岩湖）、米奇皮科滕和乌奇绿岩带以及津巴布韦的“上绿岩”。较老组包括南非的斯威士兰超群、澳大利亚的瓦拉伍纳群和印度的萨尔古尔大理岩。从矿物学角度来看，较年轻绿岩中的碳酸盐主要是石灰岩，而较老绿岩中的是铁白云石（铁白云石）；后者与热液碳酸盐有一些相似之处。在有铁矿石的矿化区域，碳酸盐矿物是菱铁矿±铁白云石，与绿岩的年龄无关。贫铁白云石代表碳酸盐生成的后期阶段，与沉积后构造断层有关。石灰岩序列的原始矿物学似乎是富锶文石。太古宙碳酸盐产生接近地幔的锶同位素值，较年轻和较老绿岩的（87Sr/86Sr）o分别为0.7025±0.0015和0.7031±0.0008。保存最完好的样本的δ1³C为+1.5±1.5‰ PDB，与显生宙的对应样本相当。相比之下，δ1⁸O的最佳估计值为-7‰ PDB。与显生宙的例子相比，太古宙石灰岩富含¹⁶O以及Mn²⁺和Fe²⁺，这些差异不是沉积后蚀变现象的结果。太古宙碳酸盐（以及海水）的矿物学和化学属性与这样的观点一致，即同期海洋的成分可能通过与“地幔”的广泛相互作用而得到缓冲，也就是说，与洋壳以及源自地幔源的同期普遍存在的火山沉积堆积相互作用。
