Abstract Early Paleozoic sandstones deposited along the northern margin of Gondwana are commonly interpreted to represent a vast, well-mixed, and far-travelled blanket of sand sourced from Neoproterozoic orogenic belts in the interior of the landmass. However, the broadly similar timing of magmatism recorded in the interior orogens of Gondwana has hindered previous attempts to identify specific sediment source regions through U Pb dating of detrital zircons. Here, we achieve a more refined view of the source-to-sink relationships across the early Paleozoic northern margin of Gondwana by integrating U Pb dating and trace element analysis of detrital rutile with U Pb dating and Hf isotopic analysis of detrital zircon. We focus on the early Cambrian Lalun Formation, in the Alborz block of Iran, which is one of the most distal exposures of the North Gondwanan sand sheet. The detrital zircon provenance of the Lalun Formation is dominated by Neoproterozoic ages (74%), with fewer pre-Neoproterozoic (22%), and rare early Cambrian (4%) age fractions. Neoproterozoic detrital zircons have variable ɛHf(t) values (−33 to +14), with a predominance of positive values (> 70%), whereas the pre-Neoproterozoic zircons define an approximately linear ɛHf(t)-time array initiating at ɛHf(t) = +7 at ∼2500 Ma and evolving to −15 by ∼1500 Ma. Detrital rutile ages from the Lalun Formation are mostly Cryogenian, with rare pre-Neoproterozoic grains. Calculated Zr-in-rutile temperatures and Cr Nb compositions imply that most of the detrital rutile was sourced from amphibolite facies metapelites. Comparing our new detrital zircon ɛHf(t) data with an extensive compilation of ɛHf(t) data from magmatic and metamorphic rocks in the East African Orogen demonstrate that the Arabian-Nubian Shield is a more suitable source for the Lalun Formation than more distal portions of the orogen (e.g., Mozambique Belt). The eastern part the Arabian-Nubian Shield also provides a suitable source for the abundant Cryogenian detrital rutile ages in the Lalun Formation. This more proximal source for the Lalun Formation reveals a complicated pattern of sediment dispersal across the northern margin of Gondwana and challenges the notion of a well-mixed, far-travelled sand sheet.

中文翻译：

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综合碎屑金红石和锆石物源揭示北冈瓦纳寒武纪砂岩的多种来源

摘要 沿着冈瓦纳大陆北缘沉积的早古生代砂岩通常被解释为代表来自大陆内部的新元古代造山带的广阔、混合良好和远行的砂层。然而，冈瓦纳大陆内部造山带中记录的岩浆活动时间大致相似，这阻碍了之前通过碎屑锆石 U Pb 定年确定特定沉积物源区的尝试。在这里，我们通过将碎屑金红石的 U Pb 测年和微量元素分析与碎屑锆石的 U Pb 测年和 Hf 同位素分析相结合，更精确地了解冈瓦纳古生代早期北缘的源汇关系。我们专注于伊朗 Alborz 区块的早期寒武纪拉伦组，这是北冈瓦纳沙床最远端的出露之一。拉伦组碎屑锆石物源以新元古代（74%）为主，前新元古代（22%）较少，早寒武世（4%）年龄分数较少。新元古代碎屑锆石具有可变的 ɛHf(t) 值（−33 至 +14），以正值为主（> 70%），而前新元古代锆石定义了一个近似线性的 ɛHf(t) 时间阵列，起始于 ɛHf (t) = +7 在 ~2500 Ma 并在 ~1500 Ma 演变到 -15。拉仑组碎屑金红石时代多为低温纪，少见前新元古代颗粒。计算出的金红石中 Zr 温度和 Cr Nb 成分表明大部分碎屑金红石来自角闪岩相变质岩。将我们新的碎屑锆石 ɛHf(t) 数据与来自东非造山带岩浆和变质岩的大量 ɛHf(t) 数据进行比较，表明阿拉伯-努比亚地盾比更远的部分更适合拉伦组的来源造山带（例如，莫桑比克带）。阿拉伯-努比亚地盾东部也为拉伦组中丰富的低温纪碎屑金红石时代提供了合适的来源。拉伦组的这个更近端的来源揭示了冈瓦纳大陆北部边缘复杂的沉积物扩散模式，并挑战了混合良好的远距离沙床的概念。