Abstract The Uatuma event is a silicic large igneous province (SLIP) covering an area of 1.500.000 km2 of the Amazonia craton at ca. 1890–1850 Ma. New paleomagnetic data and U-Pb apatite ages for coeval microgranitic, andesitic, and basaltic dykes in the Carajas Province (southeastern Amazonia craton) are presented. Two primary characteristic remanent magnetizations (ChRMs) were isolated for the Carajas dykes which were combined with published results for coeval rocks in the Sao Felix do Xingu area, producing two grand mean poles: (1) “CA1”, dated at 1880 Ma on zircon and apatite, whose mean site directions cluster around the mean Dm = 132.8°, Im = 76° (N = 26, α95 = 5°, k = 32.7), yielding the paleomagnetic pole at 328.7°E, 23.3°S, (A95 = 8.7° K = 11.7), and (2) “CA2” from well-dated microgranitic dykes of the Velho Guilherme Suite (1855 Ma U-Pb on zircon and apatite). Site mean directions group around the mean Dm = 240.3°, Im = 11.8° (N = 18, α95 = 10.8°, k = 11.1), which yielded the paleomagnetic pole at 221.3°E, 30.2°S, (A95 = 8.8°, K = 16.2). The remanent magnetization of the Velho Guilherme microgranitic dykes is carried by pseudo-single domain (PSD) magnetite. Its primary origin is supported by a positive baked contact test. Two younger secondary components were also isolated in the Carajas dyke swarm: one probably associated to the Mesozoic Central Atlantic magmatic province (CD3), and another component (CD4) with yet undefined age. A new configuration for the Amazonia and West Africa during the Paleoproterozoic, which aligns the Sassandra shear zone (in Africa) and the North Guiana Through and other shear zones (in Guiana Shield), is supported by geological and paleomagnetic data. The large angular distance between the 1880 Ma CA1 and 1855 Ma CA2 (Q ~ 6) poles that are relatively close in age implies in a high plate velocity for the Amazonia craton, which is not consistent with modern plate tectonics. A similar large discrepancy between 1880 and 1860 Ma poles was also observed at least as many as six cratons. Although other hypotheses can be invoked, such as non-uniformitarian magnetic fields, the occurrence of large-scale true polar wander at this time may be the most parsimonious explanation of the widespread discrepancies.

中文翻译：

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大约在古地理重建的新限制。1.88 Ga 来自 Carajás dyke swarm（亚马逊东部）的地质年代学和古地磁学

摘要 Uatuma 事件是一个硅质大型火成岩省 (SLIP)，覆盖约 1.500.000 平方公里的亚马逊克拉通。1890-1850 年 提供了 Carajas 省（亚马逊克拉通东南部）同时期微花岗岩、安山岩和玄武岩脉的新古地磁数据和 U-Pb 磷灰石年龄。分离出 Carajas 岩脉的两个主要特征剩磁 (ChRMs)，结合已发表的 Sao Felix do Xingu 地区同期岩石的结果，产生两个大平均极：(1) “CA1”，锆石上的日期为 1880 Ma和磷灰石，其平均位置方向聚集在平均 Dm = 132.8°，Im = 76°（N = 26，α95 = 5°，k = 32.7），在 328.7°E，23.3°S，（A95 = 8.7° K = 11.7)，(2) 来自 Velho Guilherme Suite 年代久远的微花岗质岩脉的“CA2”（锆石和磷灰石上的 1855 Ma U-Pb）。站点平均方向组围绕平均 Dm = 240.3°，Im = 11.8°（N = 18，α95 = 10.8°，k = 11.1），从而在 221.3°E，30.2°S，（A95 = 8.8° , K = 16.2)。Velho Guilherme 微花岗岩岩脉的剩磁由伪单畴 (PSD) 磁铁矿承载。它的主要来源得到了正面烘烤接触测试的支持。在 Carajas 岩脉群中还分离出两种较年轻的次生成分：一种可能与中生代中大西洋岩浆区 (CD3) 相关，另一种成分 (CD4) 的年龄尚未确定。古元古代亚马逊河和西非的新形态，将 Sassandra 剪切带（在非洲）与北圭亚那贯穿和其他剪切带（在圭亚那地盾中）对齐，得到地质和古地磁数据的支持。年龄相对较近的 1880 Ma CA1 和 1855 Ma CA2 (Q ~ 6) 两极之间的大角距意味着亚马逊克拉通的板块速度较高，这与现代板块构造不符。在 1880 年和 1860 年 Ma 极之间也观察到了类似的巨大差异，至少多达 6 个克拉通。尽管可以援引其他假设，例如非均匀磁场，但此时发生大规模真正的极地漂移可能是对广泛差异的最简洁的解释。年龄相对较近的 1880 Ma CA1 和 1855 Ma CA2 (Q ~ 6) 两极之间的大角距意味着亚马逊克拉通的板块速度较高，这与现代板块构造不符。在 1880 年和 1860 年 Ma 极之间也观察到了类似的巨大差异，至少多达 6 个克拉通。尽管可以援引其他假设，例如非均匀磁场，但此时发生大规模真正的极地漂移可能是对广泛差异的最简洁的解释。年龄相对较近的 1880 Ma CA1 和 1855 Ma CA2 (Q ~ 6) 两极之间的大角距意味着亚马逊克拉通的板块速度较高，这与现代板块构造不符。在 1880 年和 1860 年 Ma 极之间也观察到了类似的巨大差异，至少多达 6 个克拉通。尽管可以援引其他假设，例如非均匀磁场，但此时发生大规模真正的极地漂移可能是对广泛差异的最简洁的解释。