Two Cretaceous granitoid belts (i.e., the northwest and southeast belts) have been identified in Zhejiang, northeast South China Block. In this study, seven granitoid plutons from both the two belts were collected for zircon U-Pb dating, whole-rock geochemistry, Sr-Nd isotope, and zircon Hf isotope analyses. Chronologically, the Longyou (132 Ma), Sucun (136 Ma), Shanghekou (131 Ma), and Huangshitan (ca. 126 Ma) plutons from the northwest belt display older magma crystallization age than those of the Xiaoxiong (100 Ma), Zhujiajian (108 Ma), and Qingbang island (108 Ma) plutons from the southeast belt. The Sucun quartz monzonite and the Longyou, Shanghekou, Zhujiajian, and Qingbang island granites therein are fractionated I-type granites (i.e., partial melting of meta-igneous rocks) with relatively moderate-low Zr saturation temperature (723–823 °C) and pronouncedly evolved Nd and Hf isotopic compositions (εNd(t) = –8.17 to –5.67 and εHf(t) = –15.07 to –5.67), indicating that they are derivatives of ancient crustal melt-dominated magmas. The Huangshitan granite shows A-type granitic (i.e., granites that are alkaline and anhydrous and from anorogenic setting) features with high Ga/Al (3.47–5.58), rare earth element (REE) content (271–402 ppm), and Zr saturation temperature (781–889 °C). It holds less enriched Nd and Hf isotopic compositions (εNd(t) = –4.13 to –3.60 and εHf(t) = –5.90 to –2.16) and is attributed to partial melting of mature crustal materials with minor basaltic magma incorporation. The Xiaoxiong (quartz) syenitic porphyry is characterized by moderate SiO2 content (60.68–69.92 wt%), high alkali (9.03–11.66 wt%) and REE contents with fractionated REE pattern [(La/Yb)N = 13.8–26.1]. Its relatively depleted Nd and Hf isotopic compositions (εNd(t) = –3.67 to –3.42 and εHf(t) = –5.76 to –2.25) imply that it could be a derivative of basaltic magma from K-rich metasomatized mantle. Available geochronological data indicate that there were two episodic magmatic pulses at ca. 140–120 Ma and ca. 110–85 Ma associated with the Paleo-Pacific Plate underthrusting beneath the northeast South China Block. Here we put forward an episodic slab retreat and roll-back model to account for generation of these magmatic rocks. Firstly, the subducting Paleo-Pacific slab roll-back initiated at ca. 140 Ma and reached climax at ca. 130–120 Ma, which led to formation of the Longyou, Sucun, and Shanghekou I-type granites and the Huangshitan A-type granite, respectively. Subsequently, a flat slab subduction stage occurred with eastward trench retreat, causing a period of magmatic quiescence from ca. 120 to 110 Ma. The following second slab roll-back started at ca. 110 Ma and reached climax at ca. 100 Ma, giving rise to the earlier Zhujiajian and Qingbang island I-type granites and the later Xiaoxiong (quartz) syenitic porphyry.

中文翻译：

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华南地块东北部浙江白垩纪花岗岩的成因及其对古太平洋板块后退的影响

在华南地区东北部的浙江，发现了两条白垩纪花岗岩带（即西北和东南带）。在这项研究中，从两条带中收集了七个花岗岩类p，用于锆石U-Pb测年，全岩地球化学，Sr-Nd同位素和锆石Hf同位素分析。从时间上看，西北地带的龙游（132 Ma），苏村（136 Ma），上河口（131 Ma）和黄石滩（约126 Ma）岩体显示的岩浆结晶年龄比小熊（100 Ma），朱家尖的岩浆结晶年龄大。 （108 Ma）和东南邦的青榜岛（108 Ma）岩体。苏村石英蒙脱石及其中的龙游，上河口，朱家尖和青榜岛花岗岩均为分型I型花岗岩（即 较低的Zr饱和温度（723–823°C）和明显演化的Nd和Hf同位素组成（εNd（t）= –8.17至–5.67和εHf（t）= –15.07）至–5.67），表明它们是古代地壳熔融为主的岩浆的衍生物。黄石滩花岗岩具有A型花岗岩（即碱性和无水花岗岩，来自人工成因），具有高的Ga / Al（3.47–5.58），稀土元素（REE）含量（271–402 ppm）和Zr饱和温度（781–889°C）。它拥有较少富集的Nd和Hf同位素组成（εNd（t）= –4.13至–3.60和εHf（t）= –5.90至–2.16），并且归因于成熟的地壳材料的熔融，并伴有少量玄武岩浆。小熊（石英）硒斑岩的特征是中等的SiO2含量（60。68–69.92 wt％），高碱度（9.03–11.66 wt％）和REE含量具有分馏的REE模式[（La / Yb）N = 13.8–26.1]。其相对贫乏的Nd和Hf同位素组成（εNd（t）= –3.67至–3.42和εHf（t）= –5.76至–2.25）暗示它可能是富含K的交化地幔中玄武岩浆的衍生物。现有的地质年代学数据表明，在２００１处有两个偶发的岩浆脉冲。140–120 Ma，约 110-85 Ma与古太平洋板块在华南华北地块下方的逆冲作用有关。在这里，我们提出了一个间歇性的板块退缩和回滚模型来解释这些岩浆岩的产生。首先，俯冲古太平洋板块的回滚始于。140 Ma，并达到约207的高潮。130-120 Ma，导致龙游，苏村，上河口I型花岗岩和黄石滩A型花岗岩。随后，平坦的平板俯冲阶段发生，向东退缩，导致大约从１９９８年开始岩浆静止。120至110 Ma。随后的第二个平板回滚始于约。110 Ma并达到约207的高潮。100 Ma，产生较早的朱家尖岛和青邦岛I型花岗岩，以及较晚的小熊（石英）同质斑岩。