Early Miocene (21–23 Ma) high Sr/Y volcanic field in the Gangdese batholith, southern Tibet
Early Miocene (21–23 Ma) high Sr/Y volcanic field in the Gangdese batholith, southern Tibet
复制标题
DOI：
10.1016/j.lithos.2022.106807
复制
发表时间：
2022-07
期刊：
影响因子：
3.5
通讯作者：
Qian Xu;L. Zeng;Li-E. Gao
中科院分区：
文献类型：
--
作者：
Qian Xu;L. Zeng;Li-E. Gao
通过详细的岩石学、地球化学和年代学研究，揭示了冈底斯南部切瓦地区一套中新世（~21 ~ 23 Ma）英安岩组成的高Sr/Y和La/Yb火山岩及其邻近的晚白垩世（~78 ~ 80 Ma）闪长岩和闪长岩。分析结果表明：(1)英安岩具有富钠、过铝、高Sr/Y和La/Yb的特征，具有埃达质亲和性，花岗质围岩（闪长岩和闪长岩）和包裹体具有富钠和成矿特征；(2)英安岩具有相对的放射性成因Sr（86Sr/87Sr(t) = 0.7049 ~ 0.7061）、非放射性成因Nd（εNd(t) = - 3.8 ~ +0.1）和正Hf（εHf(t) = +3.0 ~ +9.5）同位素组成，而其伴生深部岩体具有相对较低的Sr（86Sr/87Sr(t) = 0.7035 ~ 0.7039）、较高的Nd（εNd(t) = +3.3 ~ +4.9）和Hf（εHf(t) = +11.1 ~ +14.7）同位素组成。研究结果表明，早中新世英安岩是由增厚的（~70 km）幼年下地壳部分熔融形成的，而晚白垩世花岗质围岩（闪长岩和闪长岩）和包裹体是由正常地壳厚度（~40 ~ 44 km）的幼年地壳部分熔融形成的。~23 Ma的英安质火山岩直接沉积在~80 Ma的深成岩上，表明冈底斯岩基在~23 Ma之前经历了一次快速的掘出，可能是由加厚的大陆岩石圈剥离引起的。
A detailed petrographic, geochemical and geochronological study reveals a suite of Miocene (~21–23 Ma) high Sr/Y and La/Yb volcanic rocks of dacite compositions and adjacent Late Cretaceous tonalite and granodiorite (~78–80 Ma) in the Qiewa of the southern Gangdese batholith. The analyses results show that (1) the dacites are characterized by Na-rich, peraluminous, high Sr/Y and La/Yb ratios, showing adakitic affinity, the granitic wall-rocks (tonalite and granodiorite) and enclave have the Na-rich and metaluminous features; and (2) the dacites have relatively radiogenic Sr (86Sr/87Sr(t) = 0.7049–0.7061), unradiogenic Nd (εNd(t) = −3.8 - +0.1), and positive Hf (εHf(t) = +3.0 − +9.5) isotope compositions, while its associated plutonic rocks have relatively lower Sr (86Sr/87Sr(t) = 0.7035–0.7039), but higher Nd (εNd(t) = +3.3 − +4.9) and Hf (εHf(t) = +11.1 − +14.7) isotope ratios. Data presented in this study demonstrates that Early Miocene dacites are generated by partial melting of thickened (~70 km) juvenile lower crust, whereas the Late Cretaceous granitic wall-rocks (tonalite and granodiorite) and enclave are derived from partial melting of juvenile crust with a normal crustal thickness (~40–44 km). Deposition of ~23 Ma dacitic volcanic rocks directly upon the ~80 Ma plutonic rocks suggests that the Gangdese batholith experienced an episode of rapid exhumation before ~23 Ma, possibly triggered by the delamination of thickened continental lithosphere.