A new combined geochronological and paleomagnetic study was carried out on the late Mesoproterozoic mafic dikes in the northeastern and central North China Craton (NCC). Three dikes were dated at 1224.2 ± 5.1 Ma, 1219.9 ± 6.0 Ma and 1215.2 ± 7.7 Ma through use of the secondary ion mass spectrometry (SIMS) zircon dating method and one dike was dated at 1219.1 ± 4.3 Ma by using SIMS baddeleyite dating method, indicating that these dikes emplaced at ∼1220 Ma. A total of 286 paleomagnetic core samples were collected from seven ∼1220 Ma dikes and their host rocks, as well as two ∼775 Ma dikes for field tests. All the samples were subjected to stepwise thermal demagnetization. Rock magnetic experiments of representative samples demonstrate that the dominant magnetic carriers of the ∼1220 Ma dikes are single-domain and pseudo-single domain magnetite grains. Two paleomagnetic components were identified from the ∼1220 Ma dikes. The low temperature component is a viscous magnetic remanence acquired in the recent geomagnetic field. The high temperature component (HTC) was isolated between 500 and 580°C, which directs east and down with moderate inclination. A paleomagnetic pole (11.3°N, 175.8°E, A95 = 7.6°) was determined by averaging seven virtual geomagnetic poles (VGPs), each VGP corresponding to the mean HTC direction of an individual dike. The ∼1220 Ma pole passed a baked-contact test and appeared to adequately average out secular variation. It differs from any younger poles of the NCC, and is thus considered as a reliable pole for the NCC. While our new results place the NCC at intermediate paleolatitudes (∼28.8°N for site located at 36.8°N, 113.4°E) at ∼1220 Ma, the coeval high-quality poles in the global paleomagnetic database, however, indicate that the Australian cratons were positioned near the pole and Laurentia was located around the Equator, depicting a dispersed paleogeographic pattern of the three continents at ∼1220 Ma. The updated paleomagnetic data together with geological evidence may suggest that the NCC separated from northern Australia between ∼1320 and ∼1220 Ma, and later joined northwestern Laurentia between ∼1220 and ∼1110 Ma.

中文翻译：

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华北克拉通约 1220 Ma 基性岩脉的地质年代学和古地磁综合研究及其对 Nuna 分裂和 Rodinia 组装的影响

对华北克拉通东北部和中部的中元古代晚期基性岩脉进行了新的地质年代学和古地磁综合研究。通过二次离子质谱（SIMS）锆石定年法测定了3条脉脉1224.2±5.1 Ma、1219.9±6.0 Ma和1215.2±7.7 Ma，1条脉岩脉采用SIMS定年法，定年时间为1219.1±4.3 Ma。表明这些岩脉发生在 ∼1220 Ma。从 7 个～1220 Ma 岩脉及其主岩中采集到 286 个古地磁岩心样品，以及 2 个～775 Ma 岩脉进行野外试验。所有样品均经过逐步热退磁。代表性样品的岩石磁性实验表明，~1220 Ma 岩脉的主要磁性载体是单畴和伪单畴磁铁矿颗粒。从~1220 Ma 岩脉中鉴定出两种古地磁成分。低温成分是在最近的地磁场中获得的粘性剩磁。高温分量 (HTC) 被隔离在 500 到 580°C 之间，向东和向下倾斜，倾斜度适中。古地磁极 (11.3°N, 175.8°E, A95 = 7.6°) 通过平均七个虚拟地磁极 (VGP) 确定，每个 VGP 对应于单个堤防的平均 HTC 方向。～1220 Ma 的极点通过了烘焙接触测试，似乎充分平均了长期变化。它不同于 NCC 的任何年轻极点，因此被认为是 NCC 的可靠极点。虽然我们的新结果将 NCC 置于中古纬度（位于 36.8°N，113.4°E 的地点为 ∼28.8°N）在 ∼1220 Ma，然而，全球古地磁数据库中的同期高质量极表明澳大利亚克拉通位于极地附近，Laurentia 位于赤道附近，描绘了约 1220 Ma 时三大洲的分散古地理格局。更新后的古地磁数据和地质证据可能表明，NCC 在 1320 至 1220 Ma 之间从澳大利亚北部分离，后来在 1220 至 1110 Ma 之间加入了劳伦西亚西北部。然而，全球古地磁数据库中同时代的优质极地表明，澳大利亚克拉通位于极地附近，劳伦西亚位于赤道附近，描绘了约 1220 Ma 的三大洲分散的古地理格局。更新后的古地磁数据和地质证据可能表明，NCC 在 1320 至 1220 Ma 之间从澳大利亚北部分离，后来在 1220 至 1110 Ma 之间加入了劳伦西亚西北部。然而，全球古地磁数据库中同时代的优质极地表明，澳大利亚克拉通位于极地附近，劳伦西亚位于赤道附近，描绘了约 1220 Ma 的三大洲分散的古地理格局。更新后的古地磁数据和地质证据可能表明，NCC 在 1320 至 1220 Ma 之间从澳大利亚北部分离，后来在 1220 至 1110 Ma 之间加入了劳伦西亚西北部。