Formation and magmatic evolution of the mangling plutonic complex in North Qinling, China
摘要
The North Qinling orogenic belt experienced Mesozoic intracontinental tectonic–magmatic activity. The Mangling plutonic complex is composed of quartz diorite, granodiorite, k-feldspar granite, monzogranite, biotite granite, and granitic porphyry in the North Qinling orogenic belt, displaying high-potassium calc-alkaline features (SiO₂ = 64.78‒73.36 wt%, Mg# = 34.02‒40.65, A/CNK = 1.24‒1.67), enriched in LILE and LREE while depleted in HFSE. Isotopic data (ISr = 0.7064~0.7087, εNd(t) = − 7.05 to − 13.97, 206Pb/204Pb = 17.61‒18.78, 207Pb/204Pb = 15.47‒15.64) and zircon Hf isotopes (1⁷⁶Lu/1⁷⁷Hf = 0.000821‒0.001780, εHf(t) = − 6.16 ~ − 11.81) suggest crustal origin with mantle component input. The Mangling plutonic complex with a large time span (150‒128 Ma) has two magmatic intrusion periods: late Late Jurassic–early Early Cretaceous and middle Early Cretaceous. A mineral electron probe reveals the changes of conditions and the depth of emplacement during rock formation. Mineral thermometry reveals the cooling trend: 740 °C (zircon Ti), 710 °C (biotite Ti), 680 °C (titanite Zr), and 640 °C (quartz Ti), emplacement depth ~ 0.1 GPa (3.3 km). The isotope and major trace elements determine the mixing ratio of different magmas, indicating the Mangling plutonic complex mixing ratio: basic magma 6%‒28%; acid magma: 72%‒93%. This complex formed by plate subduction, collision, and post-collision extension. The transformation of this tectonic environment leads to the emplacement and superposition of different periods of magma, forming plutonic complex of granite → monzogranite → granodiorite → diorite.