Geochronological and geochemical constraints on Late Cryogenian to Early Ediacaran magmatic rocks on the northern Tarim Craton: implications for tectonic setting and affinity with Gondwana

The Tarim Craton provides a geologic record of both the fragmentation of the Rodinian supercontinent and the subsequent assembly of Gondwana. However, the timing and interactions of these radically different tectonic processes remain contested. A critical part of this debate revolves around the Late Cryogenian-Ediacaran igneous rocks along the Craton’s northern margin, specifically, whether they record super-plume related Rodinian breakup or Gondwanan orogeny. To address this issue, we present zircon U-Pb-Hf isotopic data and whole rock geochemistry from Late Cryogenian to Early Ediacaran granitoids of the northern Tarim Craton. U-Pb zircon ages reveal three magmatic periods along the northern Tarim margin: ca. 660–640 Ma, 635–625 Ma and 620–600 Ma, associated with small scale felsic and mafic magmas. These granitoids have an A2-type affinity and are enriched in alkalines, but are depleted in Nb, Ta, Sr, P and Ti. Elemental data and generally negative εHf(t) values (−13.96 to 1.65) suggest that they were mainly derived from partial melting of enriched, subduction-modified lithospheric mantle triggered by upwelling of the asthenospheric mantle along the active continental margin of northern Tarim. We suggest that the Tarim Craton travelled as an isolated plate for much of the Late Neoproterozoic, near the outer part of Rodinia and subsequently Gondwana. During this time it was affected by localized and periodic subduction-related intrusion and eruption. However, within the samples of this study, there is no U-Pb-Hf isotopic and whole-rock geochemical evidence to support either super-plume-related rifting (i.e. Rodinian breakup) or Pan-African orogeny (i.e. Gondwanan assembly).

塔里木克拉通（Tarim Craton）保存了罗迪尼亚超大陆（Rodinian supercontinent）裂解以及后续冈瓦纳大陆（Gondwana）汇聚的地质记录。然而，这两种截然不同的构造过程的发生时限与相互作用仍存在争议。这场争论的核心焦点之一，聚焦于该克拉通北缘的晚成冰纪-埃迪卡拉纪（Late Cryogenian-Ediacaran）火成岩，具体而言即这些岩石是否记录了与超级地幔柱相关的罗迪尼亚裂解事件，或是冈瓦纳造山作用。为解决这一科学问题，本文报道了塔里木克拉通北缘晚成冰纪至早埃迪卡拉纪花岗质岩石（granitoids）的锆石U-Pb-Hf同位素数据与全岩地球化学数据。锆石U-Pb定年结果揭示了塔里木北缘存在三期岩浆活动：约660~640 Ma、635~625 Ma以及620~600 Ma，伴随有小规模长英质与镁铁质岩浆活动。这些花岗质岩石具有A2型亲缘性，富集碱质元素，但亏损铌（Nb）、钽（Ta）、锶（Sr）、磷（P）与钛（Ti）。元素地球化学数据以及整体为负值的εHf(t)值（-13.96至1.65）表明，它们主要源自富集且经俯冲改造的岩石圈地幔的部分熔融，该熔融过程由塔里木北缘活动大陆边缘软流圈地幔上涌所触发。我们提出，在新元古代晚期的大部分时段，塔里木克拉通作为独立板块运移，位于罗迪尼亚超大陆外缘附近，随后又处于冈瓦纳大陆周边。在此期间，它受到了局域性、周期性的俯冲相关侵入与喷发作用的影响。然而，在本次研究的样品中，并未发现能够支持与超级地幔柱相关的裂谷作用（即罗迪尼亚裂解）或泛非造山运动（Pan-African orogeny）（即冈瓦纳大陆汇聚）的锆石U-Pb-Hf同位素与全岩地球化学证据。