Abstract Syn-exhumation partial melting of the deeply subducted continental crust commonly occurs in collisional orogenic settings. The resulting felsic melts not only form granitoids, but can also modify the composition of the mantle wedge above continental subduction zones. This study investigates crustal anatexis and its role in granitoid formation and crust–mantle interaction during continental collision using new whole-rock geochemical, Sr–Nd–Hf isotope, and zircon U Pb geochronological and Lu Hf isotope data for early Paleozoic granitoids of the North Qaidam area of northern Tibet, a collisional orogen that contains ultrahigh-pressure (UHP) metamorphic rocks. Zircon U Pb dating of the granitoids in this area yielded ages betewwn 416 ± 6 Ma and 393 ± 2 Ma, coeval with the exhumation of the deeply subducted continental crust. This indicates that these granitoids formed as a result of syn-exhumation magmatism during the continental collision. Relict zircons in the granitoids yield concordant Neoproterozoic and early Paleozoic U Pb ages that are consistent with the protolith and metamorphic ages of UHP metaigneous rocks in the orogen, respectively. The granitoids have calc-alkaline to high-K calc-alkaline compositions, with total alkali contents of 4.07–8.09 wt%. They are also metaluminous to weakly peraluminous with A/CNK ratios of 0.86–1.14. They are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE), yielding arc-like trace element patterns. They also have high (87Sr/86Sr)i ratios (0.7058–0.7195) and negative eNd(t) values (−7.1 to −1.4) and have whole-rock and zircon eHf(t) values of −2.8 to +2.7 and − 8.6 to +4.7, respectively. These data indicate that the granitoids are compositionally similar to the UHP metaigneous rocks in the collisional orogen, suggesting a genetic link. This in turn indicates that the granitoids in the study area formed from magmas generated by the partial melting during the exhumation of deeply subducted continental crust. The resulting granitic melts not only generated the syn-exhumation granitoids in this area, but also caused metasomatism associated with crust–mantle interaction in continental subduction channels.

中文翻译：

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俯冲大陆地壳的同剥脱熔融：来自藏北柴北缘早古生代花岗岩的地球化学证据

摘要 深俯冲大陆地壳的同剥脱部分熔融通常发生在碰撞造山环境中。由此产生的长英质熔体不仅形成花岗岩，而且还可以改变大陆俯冲带上方地幔楔的成分。本研究利用北部早古生代花岗岩的新全岩地球化学、Sr-Nd-Hf 同位素和锆石 U Pb 年代学和 Lu Hf 同位素数据，研究了地壳贫乏及其在大陆碰撞期间花岗岩形成和壳幔相互作用中的作用藏北柴达木地区，一个包含超高压（UHP）变质岩的碰撞造山带。该地区花岗岩的锆石 U Pb 定年年龄介于 416 ± 6 Ma 和 393 ± 2 Ma，与深俯冲大陆地壳的剥露同时期。这表明这些花岗岩是大陆碰撞过程中同剥岩岩浆作用的结果。花岗岩中的残余锆石产生一致的新元古代和早古生代 U Pb 年龄，分别与造山带中超高压变火成岩的原岩和变质岩年龄一致。花岗岩具有钙碱性至高钾钙碱性成分，总碱含量为4.07-8.09 wt%。它们也是金属铝到弱过铝的，A/CNK 比率为 0.86-1.14。它们富含大离子亲石元素 (LILE) 和耗尽高场强元素 (HFSE)，产生弧状微量元素图案。它们还具有高 (87Sr/86Sr)i 比值 (0.7058–0.7195) 和负 eNd(t) 值（-7.1 至 -1.4），并且全岩和锆石 eHf(t) 值为 -2.8 至 +2.7 和 - 8.6 到 +4.7，分别。这些数据表明花岗岩在成分上与碰撞造山带中的超高压变质岩相似，表明存在遗传联系。这反过来表明研究区的花岗岩是由深俯冲大陆地壳折返过程中部分熔融产生的岩浆形成的。由此产生的花岗岩熔体不仅在该地区产生了同折返花岗岩，而且在大陆俯冲通道中引起了与壳幔相互作用相关的交代作用。这反过来表明研究区的花岗岩是由深俯冲大陆地壳折返过程中部分熔融产生的岩浆形成的。由此产生的花岗岩熔体不仅在该地区产生了同折返花岗岩，而且在大陆俯冲通道中引起了与壳幔相互作用相关的交代作用。这反过来表明研究区的花岗岩是由深俯冲大陆地壳折返过程中部分熔融产生的岩浆形成的。由此产生的花岗岩熔体不仅在该地区产生了同折返花岗岩，而且在大陆俯冲通道中引起了与壳幔相互作用相关的交代作用。