Mafic microgranular enclaves (MMEs) are common in the granodiorites from the Shima intrusion in the Ningzhen region of the Middle-Lower Yangtze River belt (MLYRB). In this paper, we report new zircon U-Pb ages, mineral and whole rock geochemical and Sr–Nd–Hf isotopic data for the Shima MMEs and their host granodiorites to constrain their petrogenesis and tectonic implication. Zircon LA-ICP-MS U-Pb dating yields ages of 101.6 ± 1.1 Ma for the host granodiorites, and 101.8 ± 1.0 Ma for the MMEs, indicating formation from coeval magmas. This magmatism was contemporaneous with the latest stage (109–100 Ma) of magmatic activity within the MLYRB. Geochemically, the Shima granitoids have geochemical signatures resembling adakites, such as high Al₂O₃ (14.78–16.48 wt%), Sr (442–685 ppm), Na₂O (>3.5 wt%), negative Nb–Ta–Ti anomalies, low Y (10.9–18.0 ppm), Yb (0.95–1.72 ppm), Sc (6.7–11.5 ppm), and resultant high Sr/Y (24.6–57.6) and La/Yb (28.3–46.6) ratios. The Shima host granodiorites are sodic, metaluminous, high-K calc-alkaline, enriched in large ion lithophile elements (LILEs; e.g., Rb, Sr, and Ba), but depleted in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), with slightly negative to positive Eu anomalies of 0.99–1.12, (⁸⁷Sr/⁸⁶Sr)_i of 0.7060 to 0.7061, ε_Nd(t) values of −10.2 to −11.7 and ε_Hf(t) of −14.1 to −16.0. The Shima MMEs have lower SiO₂ (59.81–63.81 wt%), and they are also enriched in large ion lithophile elements, depleted in high field strength elements, with slightly negative to positive Eu anomalies of 0.91–1.16, (⁸⁷Sr/⁸⁶Sr)_i of 0.7050 to 0.7061, ε_Nd(t) values of −3.9 to −10.6 and ε_Hf(t) of −13.0 to −15.7. Hornblende thermobarometry show that the Shima intrusion crystallised at temperatures of 769–832 °C and depths less than 11 km. All these petrographical, geochronological and geochemical results demonstrate that the Shima intrusion was likely formed through mixing of felsic melts derived from an ancient lower crust with mafic magmas derived from a metasomatized lithospheric mantle, coupled with fractional crystallization and minor wall-rock contamination. Our new data, combined with the regional tectonics and the temporal-spatial variation of the Mesozoic magmatism in the MLYRB, indicate that the Shima intrusion could be related with the back-arc extensional regime triggered by slab rollback of the paleo-Pacific plate.

镁铁质微细颗粒飞地（MMEs）常见于长江中下游带（MLYRB）宁镇地区的志摩侵入带的花岗闪长岩中。在本文中，我们报告了Shima MME及其宿主花岗闪长岩的新锆石U-Pb年龄，矿物和整个岩石地球化学以及Sr-Nd-Hf同位素数据，以限制其成岩作用和构造意义。锆石LA-ICP-MS U-Pb测年的年龄为宿主花岗闪长岩，年龄为101.6±1.1 Ma，而MME，年龄为101.8±1.0 Ma，表明是由近代岩浆形成的。这种岩浆作用与MLYRB内岩浆活动的最新阶段（109–100 Ma）同期。从地球化学角度看，志摩花岗岩具有类似于adakite的地球化学特征，例如高Al ₂ O ₃（14.78–16.48 wt％），Sr（442–685 ppm），Na₂ O（> 3.5 wt％），负Nb-Ta-Ti异常，低Y（10.9-18.0 ppm），Yb（0.95-1.72 ppm），Sc（6.7-11.5 ppm），以及由此产生的高Sr / Y（24.6） –57.6）和La / Yb（28.3–46.6）比率。志摩寄主花岗闪长岩是钠，金属，高K的钙碱金属，富含大型离子亲石元素（LILE；例如，Rb，Sr和Ba），但贫乏高场强元素（HFSE；例如，Nb，Ta和Ti），具有轻微的负向的正0.99-1.12 Eu异常，（⁸⁷ SR / ⁸⁶ SR）_我的0.7060到0.7061，ε_的Nd （T）的值-10.2 -11.7到和ε_的Hf （T）的- 14.1至-16.0。志摩MME的SiO ₂较低（59.81–63.81 wt％），并且它们还富含大型的离子亲石元素，而高场强元素却被耗尽，Eu异常值为0.91-1.16的负负至正，（⁸⁷ Sr / ⁸⁶ Sr）_i为0.7050至0.7061 ，ε_钕（T）的-3.9值-10.6和ε_的Hf （t）的-13.0至-15.7。Hornblende热压法显示，Shima侵入体在769–832°C的温度下结晶，且深度小于11 km。所有这些岩石学，地质学和地球化学结果都表明，志摩侵入很可能是由于将古代下地壳中的长英质熔体与交代岩石圈地幔中的镁铁质岩浆混合，形成了部分结晶和较小的围岩污染所致。我们的新数据，结合区域构造和MLYRB中生代岩浆作用的时空变化，表明志摩侵入可能与古太平洋板块回滚触发的弧后伸展机制有关。