冈底斯岩基晚白垩世镁铁质侵入岩地球化学研究

The post-Archean continental crust growth is mainly realized by arc magmatism. One puzzling aspect of the evolution of magmatic arcs is that, despite continued ocean-plate subduction beneath them, the production of melts are highly episodic. The Gangdese arc magmatism exhibits clear episodic features, renowned by the presence of magma flare-up event during 100-80Ma. There is hot debate regarding the geodynamic mechanism of this magma event, and which are mainly due to the focusing of previous studies on granitic rocks instead of mafic rocks and on the mafic rocks in the eastern part of Gangdese batholith instead of on the mafic rocks of the whole batholith. Bearing this in mind, this project designed to carry out systematical sampling and comprehensive geochemical and petrological study on the mafic intrusions from the whole Gangdese batholith, aiming to figure out the magmatic processes that occurred during the generation of these rocks and deciphering the origin of the high Sr/Y feature of these rocks. Finally, we try to figure out the geodynamic mechanism of this magma event and exert further constraints on the tectonic evolution of the New-Tethys domain through comparative study of the mafic intrusions along the strike of the Gangdese batholith.

弧岩浆作用是太古代以来大陆地壳生长的主要形式。然而，与看似静态的大洋岩石圈板块俯冲不同，弧岩浆作用普遍具有显著的幕式特征。冈底斯弧岩浆作用就是幕式弧岩浆作用的典型代表，其在晚白垩世(100-80Ma)时期出现强烈的岩浆作用。目前对这一期强烈的岩浆作用的深部动力学机制争议很大，主要是因为前人对这一期岩浆作用的研究或聚焦于花岗质岩石，抑或局限于冈底斯带东部有限地区的镁铁质岩石，没有能够更为直接的从整体上把握这期岩浆作用的特点。为此，本研究拟以冈底斯带中的镁铁质侵入岩为对象，通过对特定岩体在空间上的系统、密集采样和详细的地球化学和矿物学工作，揭示特定岩体中的岩石在形成时所经历的岩浆演化过程并重点探究它们高Sr/Y特征的成因。然后通过对冈底斯带沿走向分布的镁铁质侵入岩的对比研究，揭示其在成分和成因上的异同，并据此对该期强烈岩浆作用的深部动力学机制以及新特提斯域的构造演化历史进行进一步的限定。

弧岩浆作用是太古代以来大陆地壳生长的主要形式。然而，弧岩浆作用不仅存在沿着俯冲带和垂直俯冲带的迁移和系统的成分变化，而且存在普遍的幕式特征，这与看似静态的大洋岩石圈板块俯冲是矛盾的。本研究以冈底斯弧中部和东部地区出露的中晚白垩世(100-80 Ma)时期强烈的岩浆作用产物为研究对象，通过详细的地球化学和矿物学对比研究，揭示了这些岩石在形成时所经历的岩浆演化过程。通过对冈底斯带沿走向分布的镁铁质侵入岩的对比研究，揭示其在成分和成因上的异同，通过对白垩纪海沟沉积物的主微量和Sr-Nd-Pb同位素分析，定量表征了这些镁铁质岩石地幔源区中再循环地壳物质的性质、组成和比例。发现冈底斯造山带白垩纪岩浆作用沿走向和垂直走向的时空迁移和成分变化受控于俯冲特提斯洋板片的俯冲行为，即俯冲板片的周期性角度变化和回卷，并确立了冈底斯造山带白垩世花岗质岩石的新生地壳重熔成因。同时，结合对长江中下游地区和安第斯大陆弧岩浆岩的对比研究，深入揭示了俯冲带岩浆岩源区形成、源区熔融所伴随的地壳物质循环、壳幔相互作用以及俯冲板片回卷等深部过程，加深了对俯冲带深部动力学过程的认识。