Paleo-Pacific subduction generated a prolonged active continental margin along the coast of the South China Block (SCB). A Triassic magmatic gap was argued to have occurred and was ascribed to flat-slab subduction of an oceanic plateau. We study for the first time a >330-m-long core of typical arc volcanics dated at ca. 218 Ma from the Meiji Atoll in the southern South China Sea (SCS). Paleomagnetism suggests 4.1°± 1.5° of post-eruption southward drift. These observations clearly support the existence of a Triassic arc in the SCB and imply that part of the arc later split off and drifted southward during the opening of the SCS in the Oligocene. Our results better constrain the lateral extent of the proposed flat-slab subduction along the margin of the SCB. Moreover, we provide direct evidence of how the breakaway of ribbon continents operated in active continental margins, a recurrent scenario that has been invoked for Phanerozoic tectonics and continental growth throughout Asia.

中文翻译：

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在南海南部发现隐藏的三叠纪弧：带状大陆分离的证据对西太平洋边缘的演化有影响

古太平洋俯冲在华南陆块（SCB）沿岸形成了一个延长的活动大陆边缘。有人认为已经发生了三叠纪岩浆间隙，并将其归因于海洋高原的平板俯冲。我们首次研究了一个 > 330 米长的典型弧形火山岩心，其年代为ca. 距南海南部（SCS）明治环礁218 Ma。古地磁表明喷发后有 4.1°± 1.5° 的南移。这些观察结果清楚地支持了在 SCB 中存在三叠纪弧，并暗示部分弧后来在渐新世 SCS 打开期间分裂并向南漂移。我们的结果更好地限制了拟议的平板俯冲沿 SCB 边缘的横向范围。此外，我们提供了带状大陆分离如何在活跃大陆边缘运作的直接证据，这是一种反复出现的情景，已被用于整个亚洲的显生宙构造和大陆增长。