Abstract Insights into crust–mantle interaction in continental collisional orogens is key to understanding high- and ultrahigh-temperature (HT–UHT) metamorphism, continental crustal growth, and the tectonic evolution of such orogens. Here, we present whole-rock major- and trace-element and Nd isotope geochemistry, as well as zircon U–Pb geochronology and Hf isotope data, for quartz monzodiorites from the Helanshan Complex to constrain their petrogenesis and draw implications regarding crust–mantle interaction during formation of the Khondalite Belt in the North China Craton. LA–ICP–MS zircon U–Pb dating yields crystallization ages of 1938–1931 Ma for three samples, contemporaneous with spinel-bearing UHT pelitic granulites from the Helanshan Complex. The quartz monzodiorite samples have variable whole-rock compositions, with relatively low SiO2 (low to 51.41 wt.%) but high MgO (up to 5.05 wt.%) and Cr (up to 80.9 ppm) contents, as well as high Mg# values (up to 0.50), which suggest their derivation from the mantle. These samples exhibit a narrow range of eNd(t) values of −0.3 to +1.0, with no decrease as decreasing whole-rock MgO content, and variable zircon eHf(t) values of −2.4 to +5.8. In addition, Mg# values of hornblende and biotite, and Xan values of plagioclase decrease gradually with increasing whole-rock SiO2 content. All of these geochemical data indicate that the studied quartz monzodiorites were produced by fractional crystallization of mantle-derived magma, with assimilation of crustal material. On the basis of previously published data in the Khondalite Belt, the Helanshan quartz monzodiorites formed in the post-collisional setting, and record a tectonic transition from compression to extension during the period ca. 1.95–1.93 Ga. The emplacement of mantle-derived magma that formed the quartz monzodiorites through differentiation at ca. 1.93 Ga, was possibly responsible for the formation of ca. 1.93 Ga UHT rocks in the Helanshan Complex.

中文翻译：

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华北克拉通贺兰山杂岩古元古代后碰撞石英二闪长岩的年代学和岩石成因：对壳幔相互作用的影响

摘要 了解大陆碰撞造山带壳幔相互作用是理解高温和超高温 (HT-UHT) 变质作用、大陆地壳生长以及此类造山带构造演化的关键。在这里，我们展示了贺兰山杂岩体石英二长闪长岩的全岩主微量元素和 Nd 同位素地球化学，以及锆石 U-Pb 年代学和 Hf 同位素数据，以限制它们的成因并得出有关壳幔相互作用的影响华北克拉通孔达岩带形成过程中。LA-ICP-MS 锆石 U-Pb 测年得出三个样品的结晶年龄为 1938-1931 Ma，与来自贺兰山杂岩体的含尖晶石的 UHT 泥质麻粒岩同时期。石英二闪长岩样品具有可变的全岩成分，具有相对较低的 SiO2（低至 51.41 wt.%）但高 MgO（高达 5.05 wt.%）和 Cr（高达 80.9 ppm）的含量，以及高 Mg# 值（高达 0.50），这表明它们的推导从地幔。这些样品的 eNd(t) 值范围很窄，为 -0.3 至 +1.0，随着全岩 MgO 含量的降低，并没有降低，以及 -2.4 至 +5.8 的可变锆石 eHf(t) 值。此外，角闪石和黑云母的Mg#值和斜长石的Xan值随着全岩SiO2含量的增加而逐渐降低。所有这些地球化学数据表明，所研究的石英二闪长岩是由地幔来源的岩浆分步结晶、地壳物质同化作用产生的。根据先前发表的孔达岩带数据，贺兰山石英二闪长岩在碰撞后环境中形成，并记录大约在这一时期从压缩到伸展的构造转变。1.95-1.93 Ga。地幔源岩浆的侵位形成石英二闪长岩。1.93 Ga，可能是形成约的原因。贺兰山杂岩中的 1.93 Ga UHT 岩石。