Impact spherules from Karelia, Russia: Possible ejecta from the 2.02 Ga Vredefort impact event
Impact spherules from Karelia, Russia: Possible ejecta from the 2.02 Ga Vredefort impact event
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来自俄罗斯卡累利阿的撞击小球：可能是 2.02 Ga Vredefort 撞击事件的喷射物
DOI：
10.1130/g35231.1
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发表时间：
2014
期刊：
影响因子：
5.8
通讯作者：
Matthew S. Huber
中科院分区：
文献类型：
--
作者：
Matthew S. Huber
在俄罗斯西北部卡累利阿古元古代Zaonega组的两个岩心中发现了可能是撞击成因的球状层。球状体存在于原地角砾岩沉积白云岩的白云岩基质中。球体是毫米大小，通常是圆形的，尽管存在泪滴和哑铃形态。球状体含有高达0.75 ppb的Ir，Ru/Ir为2，表明目标岩石与次要的非晶质成分混合。Zaonega组的年龄限制在1.975 ± 0.024 Ga（Sm-Nd）和1.980 ± 0.057 Ga（Pb-Pb）以及2.050 Ga（Re-Os）之间，这包括了南非2020 Ma Vredefort撞击构造的年龄，并表明球粒层可能代表该事件的喷出物。如果这种联系得到证实，球粒的大小和岩层的厚度表明，距离撞击地点的距离小于2500公里，从而限制了古元古代晚期芬诺斯堪的纳维亚地盾和卡普瓦尔克拉通之间的古地理距离。
Spherule beds of possible impact origin have been discovered in two drill cores in the Paleoproterozoic Zaonega Formation, Karelia, northwest Russia. Spherules are found within the dolomite matrix of in-situ brecciated sedimentary dolostones. Spherules are millimeter size and generally round, although teardrop and dumbbell morphologies are present. Spherules contain up to 0.75 ppb Ir, with a Ru/Ir of 2, indicating a mixing of target rocks with a minor chondritic component. The age of the Zaonega Formation is constrained between limits of 1.975 ± 0.024 Ga (Sm-Nd) and 1.980 ± 0.057 Ga (Pb-Pb), and 2.050 Ga (Re-Os), which brackets the age of the 2020 Ma Vredefort impact structure in South Africa, and suggests that the spherule beds could represent ejecta from that event. If the link is confirmed, the size of the spherules and thickness of the beds suggest that the distance from the impact site was <2500 km, thereby constraining the paleogeographic distance between the Fennoscandian Shield and Kaapvaal craton during the late Paleoproterozoic.