Numerous Neoproterozoic intrusive rocks are distributed along the northern margin of the Yangtze Block in South China, and their petrogenesis and tectonic setting remain the subject of debate. This study systematically compiled data from igneous rocks from the northern margin of the Yangtze Block, including abundant felsic plutons with formed temperatures of >800 °C. The data reveal two high-temperature rifting-related events at ~830–780 and 750–700 Ma. Significant changes in Hf-O isotopes appeared at ~790 Ma, with later rocks exhibiting positive ε_Hf(t) and low δ¹⁸O. To clarify the nature and tectonic significance of these high-temperature events, we sampled plutonic rocks from the Lianghekou (LHK) and Dalanggou (DLG) areas of Hannan, on the northern margin of the Yangtze Block. The samples from LHK are ~785 Ma monzogranite emplaced towards the end of the first high-temperature event and derived from partial melting of thickened juvenile crust contaminated by older crustal material. These rocks have ε_Hf (t) values between +4.6 and + 11.5, δ¹⁸O values between +6.2‰ and + 7.3‰, and contain residual combinations of garnet, clinopyroxene, rutile, and amphibole. The genesis of the monzogranite is interpreted as being emplaced in an initial rifting environment and related to a super mantle plume. The DLG samples are ~743 Ma alkali feldspar granite representing the second event; they have the geochemical characteristics of a reduced A-type granite enriched in Fe and poor in Mg, FeO^T/(FeO^T + MgO) values close to 1, and emplacement temperatures of 813 °C–848 °C. The alkali feldspar granite originated from partial melting of a tholeiitic source and was influenced by extensive fractionation. It has ε_Hf(t) values of +2.5 to +10.9, δ¹⁸O values of +6.6‰ to +7.4‰, and contains residual plagioclase. The DLG alkali feldspar granite and nearby reduced A-type granite indicate that the northern margin of the Yangtze Block experienced a low oxygen fugacity environment at ~817–743 Ma. The second high-temperature event possibly reflected rifting that gradually matured after 790 Ma, at which point the mantle changed from a source of heat alone into a source of both heat and material.

华南扬子陆块北缘分布着大量新元古代侵入岩，其成因和构造背景仍是争论的焦点。本研究系统整理了扬子地块北缘火成岩资料，包括形成温度>800℃的丰富长英质岩体。数据揭示了在~830-780 和 750-700 Ma 的两个高温裂谷相关事件。Hf-O 同位素在~790 Ma 出现显着变化，后期岩石表现出正 ε _Hf (t) 和低 δ ¹⁸O. 为了阐明这些高温事件的性质和构造意义，我们对扬子地块北缘汉南两河口（LHK）和大浪沟（DLG）地区的深成岩进行了采样。来自 LHK 的样品是在第一次高温事件结束时就位的约 785 Ma 二长花岗岩，来自被较旧地壳物质污染的增厚幼年地壳的部分熔融。这些岩石的 ε _Hf (t) 值介于 +4.6 和 +11.5 之间，δ ¹⁸O 值介于 +6.2‰ 和 +7.3‰ 之间，含有石榴石、单斜辉石、金红石和闪石的残余组合。二长花岗岩的成因被解释为位于初始裂谷环境中并与超地幔柱有关。DLG 样品是~743 Ma 碱性长石花岗岩，代表第二个事件；它们具有还原型A型花岗岩的地球化学特征，即富铁、贫镁，FeO ^T /(FeO ^T  + MgO)值接近1，侵位温度为813℃～848℃。碱长石花岗岩起源于拉斑玄武岩源的部分熔融，并受到广泛分馏的影响。它的 ε _Hf (t) 值为 +2.5 至 +10.9，δ ¹⁸O值为+6.6‰至+7.4‰，并含有残留斜长石。DLG碱长石花岗岩和附近的还原A型花岗岩表明扬子地块北缘在~817-743 Ma经历了低氧逸度环境。第二次高温事件可能反映了790 Ma之后逐渐成熟的裂谷，此时地幔从单独的热源转变为热源和物质源。