Geochronological, geochemical, and Sr–Nd–Pb–Hf isotopes of Cretaceous gneissic granite and quartz monzonite in the Tongbai Complex: Record of lower crust thickening beneath the Tongbai orogen,Geological Journal

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Geochronological, geochemical, and Sr–Nd–Pb–Hf isotopes of Cretaceous gneissic granite and quartz monzonite in the Tongbai Complex: Record of lower crust thickening beneath the Tongbai orogen
Geological Journal ( IF 1.4 ) Pub Date : 2021-04-26 , DOI: 10.1002/gj.4154
Pan‐Pan Niu _{1,

2} , Shao‐Yong Jiang _{1,

2,

3}

Affiliation

A comprehensive study of zircon U–Pb ages, major and trace elements, whole-rock Sr–Nd–Pb isotopes and zircon Hf isotopes of the gneissic granite and quartz monzonite in the Tongbai Complex is conducted in an attempt to unravel their petrogenesis and shed new light on the tectonic evolution and crust thickening process of the Tongbai orogen. Zircon U–Pb dating indicates that the emplacement of gneissic granite was early at 144.2 ± 1.3 Ma, whereas the quartz monzonite formed later at 130.2 ± 1.7 Ma. Both the gneissic granite and quartz monzonite samples share many chemical similarities, such as high Al₂O₃, K₂O, Sr contents and low MgO contents, together with high Sr/Y, high La/Yb ratios, suggesting an C-adakitic affinity and possibly derived from partial melting of the thickened lower crust. The later quartz monzonites may have involvement of much more proportion of mantle-derived materials (such as the metamorphosed mafic rocks, ecologite) in the lower crust during partial melting for its petrogenesis, due to its higher MgO, Cr, Ni, and V contents than the gneissic granites. The formation of the gneissic granite and quartz monzonite records the evolution history for the lower crust thickening beneath the Tongbai orogen at the Cretaceous. Nearly all granitoids in the Tongbai orogen currently found have an emplacement age of >130 Ma and have higher Sr/Y ratios and lower MgO, Cr, Ni, and V contents with respect to the granitoids in the Dabie orogen which occurs in two stages of granitic magmatism of >130 Ma and <130 Ma. The Tongbai orogen lacks the granitoids formed by significant crust–mantle mixing that occurred in the Dabei area at <130 Ma. These results indicate that the lower crust was continuing thickening but probably not delaminated beneath the Tongbai orogeny during the Early Cretaceous.

中文翻译：

桐柏杂岩中白垩纪片麻花岗岩和石英二长岩的年代学、地球化学和Sr-Nd-Pb-Hf同位素：桐柏造山带下地壳增厚记录

对桐柏杂岩中片麻岩和石英二长岩的锆石U-Pb年龄、主微量元素、全岩Sr-Nd-Pb同位素和锆石Hf同位素进行综合研究，试图解开它们的成因和脱落桐柏造山带构造演化与地壳增厚过程的新认识. 锆石 U-Pb 测年表明片麻岩的侵位早于 144.2±1.3 Ma，而石英二长岩则晚于 130.2±1.7 Ma。片麻岩和石英二长岩样品具有许多化学相似性，例如高 Al ₂ O ₃、K ₂O、Sr 含量和低 MgO 含量，以及高 Sr/Y、高 La/Yb 比率，表明 C-埃达克亲和可能源自增厚的下地壳的部分熔融。后期石英二长岩由于其MgO、Cr、Ni、V含量较高，可能在其成岩作用的部分熔融过程中，在下地壳中卷入了更多比例的地幔衍生物质（如变质基性岩、生态岩）比片麻花岗岩。片麻岩和石英二长岩的形成记录了白垩纪桐柏造山带下地壳增厚的演化历史。目前发现的桐柏造山带中几乎所有花岗岩的侵位年龄都>130 Ma，具有较高的Sr/Y比和较低的MgO、Cr、Ni、大别造山带中花岗岩类的 V 和 V 含量发生在 >130 Ma 和 <130 Ma 两个花岗岩岩浆作用阶段。桐柏造山带缺乏大北地区<130 Ma时发生的显着壳幔混合形成的花岗岩。这些结果表明，早白垩世，桐柏造山带下地壳继续增厚，但可能没有分层。

更新日期：2021-04-26

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