The First Discovery of Archean Dolerite Dikes in the Western Part of the Aldan Shield

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
K. G. Erofeeva, Yu. O. Larionova, A. V. Samsonov
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引用次数: 0

Abstract

Dolerite dikes were studied in the western part of the Aldan terrane, in the middle reaches of the Tokko River. These dolerite dikes form a swarm of submeridional trend about 1 km wide. The dolerites of the thickest dike preserve their primary textural and structural features and mineral composition: plagioclase + pigeonite + augite + titanomagnetite. Dolerite in the chilled margins and central parts of the dike are homogeneous in composition, corresponds to low-Mg tholeiites, has low contents of Ti and other HFSE, with weak enrichment in light REE and small negative Nb anomalies. Sm–Nd isotope data on magmatic minerals of dolerite from the central part of the dike yield a good linear regression in an isochron diagram that gives to an age of 2510 ± 64 Ma, which probably corresponds to the crystallization age of the basalt. Metadolerites in a thin dike retain plagioclase porphyritic structures, but the pyroxenes are completely replaced by amphibole and chlorite. The metadolerites are contrastingly different in low contents of MgO, Cr, and Ni and in higher contents of TiO2, Fe2O3, P2O5, Nb, and all REE. The differences in the composition of the dikes may be explained by the longterm (about 65%) crystallization differentiation of the initial melt and the emplacement of the residual melt from a shallow intermediate magma chamber via opening cracks. Such conditions probably may have existed in tectonically stable intraplate settings. The age of the dolerites of the dike swarm is comparable to that of the anorogenic granites of the Nelyuki complex (~2.4–2.5 Ga), which are widespread in the western part of Aldan granulite–gneiss terrane. Our data bridge some gaps in characteristics of intraplate anorogenic magmatism that occurred in the western Aldan Shield in the Late Archean and marked the final consolidation of a large block of Archean crust in the Chara–Olekma granite–greenstone area.

Abstract Image

在阿尔丹地盾西部地区首次发现阿新纪辉绿岩尖峰
摘要 在托克河中游的阿尔丹地层西部研究了辉绿岩堤。这些辉绿岩堤形成了一个宽约 1 公里的潜势群。最厚的辉绿岩堤保留了其主要的纹理和结构特征以及矿物成分:斜长石+白云石+橄榄石+榍石。冷硬边缘和堤坝中央部分的辉绿岩成分均一,属于低镁透辉石,钛和其他高频闪长岩含量较低,轻稀土元素富集较弱,铌负异常较小。来自堤坝中部的辉绿岩岩浆矿物的 Sm-Nd 同位素数据在等时线图中产生了良好的线性回归,得出了 2510 ± 64 Ma 的年龄,这可能与玄武岩的结晶年龄相符。薄堤中的偏闪长岩保留了斜长石斑状结构,但辉石完全被闪石和绿泥石取代。这些辉绿岩在氧化镁、铬和镍的含量较低,而在二氧化钛、三氧化二铁、五氧化二磷、铌和所有稀土元素的含量较高方面存在明显差异。岩钉的成分差异可能是由于初始熔体的长期(约 65%)结晶分异以及残余熔体通过开口裂缝从浅层中间岩浆室移出造成的。这种情况很可能存在于构造稳定的板块内部环境中。堤群中的辉绿岩的年龄与Nelyuki复合体的奥陶系花岗岩的年龄(约2.4-2.5 Ga)相当,后者广泛分布于阿尔丹花岗岩-片麻岩地层的西部。我们的数据弥补了板内阳离子岩浆活动特征方面的一些空白,这些活动发生在晚阿尔歇世阿尔丹地盾西部,标志着Chara-Olekma花岗岩-绿岩地区一大块阿尔歇世地壳的最终整合。
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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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