U–Pb Detrital Zircon Geochronology and Its Tectonic Implications for the Middle Devonian at the Northwestern Margin of the Yangtze Block

The tectonic nature of the Yangtze Block during the Middle Devonian and its paleogeographic relationship with Gondwana are critical for understanding the mid-Paleozoic tectonic evolution of East Asia. We present an integrated study of detrital zircon U-Pb geochronology, sedimentary petrology, and structural analysis of the Middle Devonian Yangmaba and Guanwushan formations at the northwestern margin of the Yangtze Block. Detrital zircon age spectra show three major peaks: 1000-900 Ma (Grenvillian), 850-720 Ma (Rodinia breakup), and 650-500 Ma (Pan-African-Caledonian). These age patterns correlate strongly with those of pre-Devonian strata within the Yangtze Block but differ significantly from Gondwanan terrains (e.g., Tethyan Himalaya and Western Australia). This distinct signature clearly indicates that the provenance of the Yangtze Block during the Middle Devonian was not directly derived from the synchronous detrital input from Gondwana. Paleoproterozoic (∼1600 Ma) and Archean (∼2500 Ma) zircons were derived exclusively from the Yangtze Craton basement, indicating dominant sediment recycling from underlying strata. Tectono-sedimentary analyses indicate that the Early Paleozoic foreland basin was transformed into an intracratonic depression during the Middle Devonian. Regional uplift led to extensive erosion of Silurian strata, forming a "recycled sediment system" that shifted provenance from orogenic input to intracratonic reworking. Sedimentary evidence supports this transition: sandstones exhibit high textural maturity and high compositional maturity, distinct from typical foreland basin fills. Our study demonstrates that Middle Devonian sediments were mainly sourced from intracratonic recycling, with Gondwana-type zircon ages representing inherited records from early Paleozoic external inputs that were subsequently reworked during the Middle Devonian. These findings not only provide evidence that the Yangtze Block was not directly derived from Gondwana during the Middle Devonian but also offer key geological constraints for clarifying the Mesozoic evolutionary history of the Yangtze Block and reconstructing its tectonic affinity with Gondwana. In summary, this study reaches a clear conclusion: during the Middle Devonian, the Yangtze Block received no synchronous detrital input from Gondwana, and its detrital materials were not directly sourced from Gondwana but originated from the sedimentary recycling of underlying strata.