冈底斯西段麻木早白垩世岩浆岩岩石成因及地质意义

青藏高原冈底斯带发育有大量的岩浆岩，本文对中拉萨地块西段南缘革吉县西南麻木地区的花岗斑岩和流纹质晶屑凝灰岩进行了详细的岩石学、岩石地球化学、锆石微量元素和锆石Hf同位素研究，综合讨论了其岩浆成因及源区深部过程。麻木研究区内的花岗斑岩和流纹质晶屑凝灰岩属于早白垩世同期岩浆作用的产物，均属于钾玄质岩石，富集大离子亲石元素和轻稀土元素，亏损高场强元素和Eu,具有较高负值的εHf(t)值，分别为-9.57～-3.43和-8.79～-4.80,以及较古老的Hf同位素地壳模式年龄t_DM2,分别为1 774～1 388 Ma和1 727～1 477 Ma。研究区早白垩世岩浆岩源于古老下地壳物质的重熔，并有少量地幔物质的加入，经历了岩浆混合后角闪石、长石和黑云母等矿物的分离结晶，最终形成了花岗斑岩和流纹质晶屑凝灰岩。结合前人和本文的研究认为研究区早白垩世岩浆作用的主要诱发机制可能为南向俯冲的班公湖-怒江洋板片回转。

Petrogenesis and geological significance of the Mamu Early Cretaceous magmatic rocks in the western part of Gangdese

A large number of magmatic rocks were formed in the Gangdese belt of the Qinghai-Tibet Plateau. To better understand the petrogenesis, magma source region and evolution, we have studied the petrography, geochemistry, zircon trace elements and Hf isotope analysis of the granite porphyry and rhyolitic crystal tuff in Mamu, Gakyi, western of the Central Lhasa Terrane. The granite porphyry and rhyolitic crystal tuff in Mamu were both formed at Early Cretaceous period. They are both shoshonitic rocks, enriched in large ion lithophile elements, and light rare earth elements, and depleted in high field-strength elements(HFSE) and Eu. They have high negative εHf(t) values of -9.57~-3.43 and -8.79~-4.80, and the older Hf isotopic crustal model age t_DM2 of 1 774~1 388 Ma and 1 727~1 477 Ma, respectively. The Early Cretaceous magmatic rocks originated from the remelting of ancient lower crustal materials, with the mixing of mantle material. After the magma mixing, the amphibole, feldspar and biotite were first separated and crystallized, finally formed the granite porphyry and rhyolitic crystal tuff. Combined with previous studies and this paper, we infer that the Early Cretaceous magmatism in Mamu is probably due to the southward subduction of the southward subduction of Bangong-Nujiang suture zone.