Several kilometers of rapid uplift in the past 2–3 million years in the Greater Caucasus in Russia has produced world-class exposures of Pliocene-Pleistocene age granites and ignimbrites at the Tyrnyauz and Chegem volcanic centers just to the east of Europe's highest mountain and active volcano, Mount Elbrus. This represents one of the world's best-preserved examples of silicic magmatism in a continental collision environment. We report results of a multi-method zircon petrochronologic (U--Pb, O--Hf isotopes, trace elements) investigation of six ignimbrites, lavas, and associated granodioritic porphyries from these localities. We observe two pulses of magmatism at 2.92 and 1.98 Ma related to Chegem and Tyrnyauz, respectively. High precision CA-ID-TIMS dating of zircons from the top and bottom of the Chegem ignimbrite and its associated porphyry yield indistinguishable age spectra recording 160 kyr of magma assembly and differentiation, with 2.9181 ± 0.0014 Ma eruption age as is constrained by the youngest dated zircon population. Together with overlapping O and Hf isotopic values, this suggests that they represent a large volume of pre-eruptively homogenized magma with ~20% crystals. Zircons have isotopically diverse cores (δ¹⁸O = +3.4–6.7‰, ε_Hf = +0.8 to +5.6) while the rims (+5.75 ± 0.20‰, ε_Hf = 3.3 ± 0.7) are in isotopic equilibrium with associated unaltered glass and major phenocryst phases. The neighboring and younger ignimbrites and granites of the nearby Elbrus and Tyrnyauz centers have overlapping higher δ¹⁸O and lower ε_Hf zircon values and cluster narrowly in age around 1.98 Ma, suggesting a common source for all these ignimbrites, likely in the Tyrnyauz area. Isotopic data for Chegem, Elbrus and Tyrnyauz zircons and rocks require the contribution of a high proportion (25–55%) of Paleozoic crust to magma petrogenesis.

The origin of sudden spikes of voluminous silicic magmatism is further investigated using thermomechanical modeling of the collisional environment. We show that the voluminous silicic volcanism at Chegem, Tyrnyauz and Elbrus is best explained by heating of the lower crust by asthenospheric upwelling after a relict slab detached and sank into the mantle at approximately 5 Ma. This timing is coincident with both the beginning of rapid uplift of the Greater Caucasus and initiation of major volcanism. After this initial melting, continuing delamination of the lithosphere and lower crust from the subducting plate produced broad mantle melting and basaltic volcanism, potentially explaining continued regional-scale magmatism in both the Greater and Lesser Caucasus.

在过去的2到300万年间，俄罗斯大高加索地区发生了数公里的快速隆升，在欧洲最高的山峰和活跃的东部的Tyrnyauz和Chegem火山中心产生了上新世至更新世时代的花岗岩和火成岩。火山，厄尔布鲁士峰。这代表了在大陆碰撞环境中保存最完好的硅质岩浆作用之一。我们报告了来自这些地区的六个火成岩，熔岩和相关的花岗斑岩的多方法锆石岩石年代学（U-Pb，O-Hf同位素，微量元素）研究的结果。我们分别在2.92和1.98 Ma观察到两个与Chegem和Tyrnyauz有关的岩浆脉冲。Chegem火成岩顶部和底部的锆石的高精度CA-ID-TIMS测年及其相关的斑岩产生的不可分辨的年龄谱，记录了160年的岩浆聚集和分化，其中2.9181±0.0014 Ma的喷发年龄受到了最年轻的年代的约束锆石种群。加上重叠的O和Hf同位素值，这表明它们代表了大量的喷发前均质的岩浆，晶体约20％。锆石具有同位素不同的核（δ¹⁸ O = + 3.4-6.7‰，ε_的Hf  = 0.8至5.6），而轮辋（5.75±0.20‰，ε_的Hf  = 3.3±0.7）与相关联的未改变玻璃和主要斑晶相同位素平衡。邻近的和年轻的熔结凝灰岩和附近的厄尔布鲁士和特尔内奥兹中心的花岗岩具有重叠越高δ ¹⁸ O和降低ε_铪年龄围绕1.98马云狭隘锆值和集群，表明所有这些熔结凝灰岩一个共同的来源，可能在特尔内奥兹区域。Chegem，Elbrus和Tyrnyauz锆石和岩石的同位素数据要求古生代地壳对岩浆成岩的贡献很大（25-55％）。

利用碰撞环境的热力学模型进一步研究了大量硅质岩浆作用突然尖峰的起源。我们显示，在遗骸板块分离并沉入地幔中约5 Ma后，软流圈上升流加热了下地壳，是对Chegem，Tyrnyauz和Elbrus巨大的硅质火山作用的最好解释。这一时机与大高加索地区的快速隆升的开始和主要火山活动的开始相吻合。在最初的融化之后，岩石圈和俯冲板块下部地壳的持续分层产生了广泛的地幔融化和玄武质火山作用，这可能解释了高加索地区和小高加索地区的区域性岩浆活动持续。