Timing of deposition and deformation of the Moodies Group (Barberton Greenstone Belt, South Africa): Very-high-resolution of Archaean surface processes
Timing of deposition and deformation of the Moodies Group (Barberton Greenstone Belt, South Africa): Very-high-resolution of Archaean surface processes
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穆迪群沉积和变形的时间（南非巴伯顿绿岩带）：太高分辨率的太古宙表面过程
DOI：
10.1016/j.precamres.2013.03.021
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发表时间：
2013
影响因子：
3.8
通讯作者：
Byerly
中科院分区：
文献类型：
--
作者：
Heubeck;Engelhardt;Byerly
巴伯顿绿岩带（BGB）中东部穆迪群冲积、河流和边缘海相硅质岩地层中的薄且大部分不连续的火山凝灰岩层含有稀有至丰富的锆石。对五个凝灰岩层和一个横切岩墙中的岩浆锆石颗粒进行了年龄测定，结果跨越了从约1000年到约1000年的整个BGB历史。3550 Ma至3215 Ma，并显示不同程度的沉积后蚀变，直到约。2500Ma。CA-ID-TIMS分析凝灰岩中最年轻的原始锆石颗粒化学磨损离子溶解热离子质谱法测得Concordia年龄在3227.6±0.3 ~ 3216±0.3Ma之间，并通过LA-SF-ICP-MS分析这些颗粒（激光烧蚀-扇形场-电感耦合等离子体质谱）和SHRIMP（灵敏高分辨率离子探针）测得的年龄介于3228±9和3214± 9 Ma之间。这些年龄中的大多数要么是相同的（误差范围内），要么比CA-ID-TIMS年龄（3223.4±0.3Ma）更老，后者是从下层无花果树群顶部Schoongezicht组凝灰岩层的锆石颗粒中获得的。我们解释这个年龄标志着火山爆发的时间，而显着的年龄和重叠的年龄的地层较高穆迪凝灰岩锆石颗粒点要么是一个高度的岩浆遗传和/或碎屑贡献周围的沉积岩期间或之后的灰凝灰岩沉积。Moodies群沉积物和变形的最小年龄由一个横切Moodies褶皱地层的未变形长英质岩脉的LA-ICP-MS锆石U-Pb年龄（3219± 9 Ma）提供。该年龄与穆迪群上部凝灰岩层的精确CA-ID-TIMS锆石U-Pb年龄（3216.0±0.3Ma）相重叠。总的来说，新的年龄数据共同意味着高达3.7km厚，砂岩为主的穆迪群的沉积和变形在<1- 14 Ma，穆迪地层因此有可能提供与主动和被动边缘第四纪地层（0.1- 1 mm/a）相当的时间分辨率。
Thin and largely discontinuous volcanic tuff beds in the alluvial, fluvial, and marginal-marine siliciclastic strata of the Middle Archaean Moodies Group, Barberton Greenstone Belt (BGB), contain rare to abundant zircon. Dating of magmatic zircon grains from five tuff beds and one cross-cutting dike yield ages which span the entire spectrum of BGB history from ca. 3550Ma to 3215Ma and show variable degrees of post-depositional alteration until ca. 2500Ma. The youngest pristine zircon grains in all tuff samples analyzed by CA-ID-TIMS (Chemical-Abrasion Ion-Dissolution Thermal Ion Mass Spectrometry) yield upper intercept and Concordia ages between 3227.6±0.3 and 3216±0.3Ma, and those grains analyzed by LA-SF-ICP-MS (Laser Ablation-Sector Field-Inductively Coupled Plasma-Mass Spectrometry) and SHRIMP (Sensitive High-Resolution Ion Microprobe) yield ages between 3228±9 and 3214±9Ma. Most of these ages are either identical (within error) or significantly older than a CA-ID-TIMS age of 3223.4±0.3Ma, obtained from zircon grains of a tuff horizon of the Schoongezicht Formation at the top of the underlying Fig Tree Group. We interpret this age to mark the time of volcanic eruption, whereas the significantly older and overlapping ages of the stratigraphically higher Moodies tuff zircon grains point either to a high degree of magmatic inheritance and/or a detrital contribution from surrounding sedimentary rocks during or after ash-tuff deposition. The minimum age for deposition of Moodies Group sediments and deformation is provided by a LA-ICP-MS zircon U-Pb age of 3219±9Ma obtained from an undeformed felsic dike which crosscuts folded Moodies strata. This age overlaps with a precise CA-ID-TIMS U-Pb zircon age of 3216.0±0.3Ma obtained from a tuff horizon of the upper Moodies Group. Overall, the new age data collectively imply that the up to 3.7km-thick, sandstone-dominated Moodies Group was deposited and deformed within <1–14Ma, and that Moodies strata thus hold the potential to offer a temporal resolution comparable to active- and passive-margin Quaternary strata (∼0.1–1mm/a).
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DOI：
--
发表时间：
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DOI：
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发表时间：
2010
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