Monazita em veios de quartzo da Serra do Espinhaço Meridional(MG): mineralogia, idades LA-ICP-MS e implicações geológicas
Monazita em veios de quartzo da Serra do Espinhaço Meridional(MG): mineralogia, idades LA-ICP-MS e implicações geológicas
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Monazita em veios de Quartos da Serra do Espinhaço Meridional(MG)：矿物学、LA-ICP-MS 和地质暗示
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发表时间：
2010
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通讯作者：
Bernhard Bühn
中科院分区：
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作者：
M. .. S. C. Chaves;P. R. Brandão;Bernhard Bühn
由于在埃斯皮纳哈科山脉南部石英脉切割岩中发现了独居石，对布恩波利斯、Olhos d‘Agua和Diamantina三个地区的独居石矿床的地质和矿物化学进行了研究，并对Diamantina和Olhos d’A gua样品进行了U-Pb激光烧蚀MC-ICPMS测年。在布埃诺波利斯，独居石标本以孪晶的形式常见，产于埃斯皮纳科超群与Macaubas群之间接触带的堆积砾石沉积中。Olhos d‘Agua矿体位于Macaubas群的变质泥质岩中，呈公制椭圆形，已在那里发现了大晶体。在Diamantina，人们研究了在Caete-Mirim河附近的堆积物中发现的破碎颗粒的毫米级独居石。当然，在第一和第三种情况下，这些颗粒来自丰富的区域石英脉。电子探针分析显示，这三种沉积物的氧化物值相似，但具有一些化学特性。这些样品已被鉴定为独居石-(Ce)，局部富Nd；Diamantina和Olhos d‘Agua矿床似乎有一些化学相似之处，尽管总体上这两个矿床没有绝对相似之处。U-Pb结果显示~491My的年龄可能表明矿物的结晶年龄，而490-440My之间的完全延长可能意味着较晚的重新加热期。在地质学术语中，这样的年龄可以标志着该地区与布拉西利亚诺旋回有关的最后事件。
Due to the discovery of monazite occurrences in an uncommon geologic setting, in quartz veins cutting rocks of the Southern Espinhaco Range, a study was carried out on the geology and mineral chemistry of these deposits in three localities ( Buenopolis, Olhos d’Agua and Diamantina) , as well as to make U-Pb laser ablasion MC-ICP-MS geochronological determinations in the Diamantina and Olhos d ’A gua samples. In Buenopolis, monazite specimens are common as twin crystals, occurring in colluvial gravel deposits in a contact zone between the Espinhaco Supergroup with the Macaubas Group. The Olhos d’Agua occurrence is in metric oval-shaped pockets within metapelitic rocks of the Macaubas Group, where large crystals have been discovered. In Diamantina, millimeter-size monazites were studied as broken grains recovered in a colluvial deposit near the Caete-Mirim river. Certainly in the first and in the third cases, such grains came from the abundant regional quartz veins. Electron microprobe analyses showed similar oxide values for the three deposits, but with some chemical specific aspects. The samples have been identified as monazites-(Ce), locally Nd-rich; the Diamantina and Olhos d’Agua deposits seem to have some chemical similarities, although in general there are no absolute resemblance between the two deposits. The U-Pb results showed an older age of ~491 My that probably indicates the crystallization age of the mineral, and a complete extension between 490-440 My that could mean a later reheating periods. In geological terms, such ages can signify the last events related to the Brasiliano Cycle in the region.