The Southward Extension of Cathaysia Block: Evidence from Zircon U‐Pb Dates of Borehole Volcanics in the Northern South China Sea
The Southward Extension of Cathaysia Block: Evidence from Zircon U‐Pb Dates of Borehole Volcanics in the Northern South China Sea
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DOI：
10.1111/1755-6724.12135
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发表时间：
2013-10
期刊：
影响因子：
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通讯作者：
Xu Changhai;Qu Xiaoming;Shi Hesheng;Zhou Zu-yi;M. Changqian
中科院分区：
文献类型：
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作者：
Xu Changhai;Qu Xiaoming;Shi Hesheng;Zhou Zu-yi;M. Changqian
通过 LA-ICP-MS 锆石 U-Pb 定年分析了从南海北部采集的五块古近纪火山岩样本，分别包括来自 Borehole SCSV1 的玄武岩和安山岩以及来自 Borehole SCSV2 的火山团块。总共 162 个锆石 U-Pb 测年涵盖了从新太古代到始新世的年龄范围，其中古新世前的数据占主导地位。古近纪年代为62.5±2.2 Ma和42.1±2.9 Ma，与南海盆地打开之前的两次火成岩事件有关。这些前古新世锆石是继承性锆石，大多具有岩浆振荡带，具有地壳锆石的稀土元素特征。 SCSV1火山岩的锆石U-Pb定年为2518-2481 Ma、1933-1724 Ma和1094-1040 Ma，SCSV2火山岩的锆石U-Pb定年为2810-2718 Ma、2458-2421 Ma和1850-993.4 Ma，揭示了南海北部前寒武纪演化的部分内容。与华夏地块的年龄记录非常相似。 SCSV2 的 927.0±6.9 Ma 和 781±38 Ma 数据分别与扬子地块和华夏地块的合并以及罗迪尼亚地块的裂解相一致。我们的火山样本中广泛发现了华夏地块加里东造山运动的年龄记录，SCSV1 的平均年龄为 432.0±5.8 Ma，SCSV2 的平均年龄为 437±15 Ma。南海北部类似华夏的部分经历了印支期和燕山期构造热事件。 SCSV1的年龄特征为266.5±3.5 Ma、241.1±6.0 Ma、184.0±4.2 Ma、160.9±4.2 Ma和102.8±2.6 Ma，SCSV2的年龄特征为244±15 Ma、158.1±3.5 Ma、141±13 Ma和96.3±2.1妈。钻孔火山岩锆石的古近纪前U-Pb年龄谱表明，南海北部经历了前寒武纪基底形成、加里东造山运动、印支造山运动到燕山期岩浆作用的演化过程。这一过程可以很好地与华南构造演化相比较，很大程度上支撑了南海北部地区作为华夏向南延伸的一部分。
Five Paleogene volcanics sampled from the northern South China Sea were analyzed via LA‐ICP‐MS zircon U‐Pb dating, including basalt and andesite from Borehole SCSV1 and volcanic agglomerate from Borehole SCSV2, respectively. A total of 162 zircon U‐Pb dates for them cover an age range from Neoarchean to Eocene, in which the pre‐Paleocene data dominate. The Paleogene dates of 62.5±2.2 Ma and 42.1±2.9 Ma are associated with two igneous episodes prior to opening of South China Sea basin. Those pre‐Paleocene zircons are inherited zircons mostly with magmatogenic oscillatory zones, and have REE features of crustal zircon. Zircon U‐Pb dates of 2518–2481 Ma, 1933–1724 Ma, and 1094–1040 Ma from the SCSV1 volcanics, and 2810–2718 Ma, 2458–2421 Ma, and 1850–993.4 Ma from the SCSV2 volcanics reveal part of Precambrian evolution of the northern South China Sea, well comparable with age records dated from the Cathaysia block. The data of 927.0±6.9 Ma and 781±38 Ma dated from the SCSV2 coincide with amalgamation between Yangtze and Cathaysia blocks and breakup of the Rodinia, respectively. The age records of Caledonian orogeny from the Cathaysia block are widely found from our volcanic samples with concordant mean ages of 432.0±5.8 Ma from the SCSV1 and of 437±15 Ma from the SCSV2. The part of the northern South China Sea resembling the Cathaysia underwent Indosinian and Yanshannian tectonothermal events. Their age signatures from the SCSV1 cover 266.5±3.5 Ma, 241.1±6.0 Ma, 184.0±4.2 Ma, 160.9±4.2 Ma and 102.8±2.6 Ma, and from the SCSV2 are 244±15 Ma, 158.1±3.5 Ma, 141±13 Ma and 96.3±2.1 Ma. Our pre‐Paleogene U‐Pb age spectra of zircons from the borehole volcanics indicate that the northern South China Sea underwent an evolution from formation of Precambrian basement, Caledonian orogeny, and Indosinian orogeny to Yanshannian magmatism. This process can be well comparable with the tectonic evolution of South China, largely supporting the areas of the northern South China Sea as part of southward extension of the Cathaysia.