Mesozoic to Cenozoic magmatic history of the Pamir
Mesozoic to Cenozoic magmatic history of the Pamir
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DOI：
10.1016/j.epsl.2017.10.041
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发表时间：
2018-01
影响因子：
5.3
通讯作者：
J. Chapman;Shane H. Scoggin;P. Kapp;B. Carrapa;M. Ducea;J. Worthington;Ilhomjon Oimahmadov;M. Gad
中科院分区：
文献类型：
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作者：
J. Chapman;Shane H. Scoggin;P. Kapp;B. Carrapa;M. Ducea;J. Worthington;Ilhomjon Oimahmadov;M. Gad
帕米尔山脉中生代火成岩和碎屑矿物的新年代学、地球化学和同位素数据有助于区分主要区域岩浆活动并约束帕米尔造山系统的构造演化。在晚三叠世至早侏罗世期间，中帕米尔地体和南帕米尔地体最终增生后，帕米尔基本上是无岩浆的，直到120-100 Ma之间的中间体（SiO 2 > 60 wt.%）、钙碱性和同位素演化（− 13 至− 5 锆石 ε Hf (t)）南帕米尔岩基就位，这是体积上最重要的帕米尔高原的岩浆杂岩，包括约 105 Ma 的高通量岩浆事件。南帕米尔岩基被解释为白垩纪喀喇昆仑岩基的北部（内侧）等效物和西藏拉萨地体北部早白垩世岩浆带的沿走向等效物。拉萨地体北部的特征是在约 110 Ma 处发生了类似的高通量事件。白垩纪中期大陆弧岩浆活动向南帕米尔地体的迁移被解释为反映了新特提斯大洋岩石圈向北的低角度至平板俯冲。帕米尔地区晚白垩世岩浆活动（80-70 Ma）很少，但集中在南帕米尔地体中部和北部，其镁铁质（SiO 2 < 60 wt.%）、碱性和同位素幼体（− 2 至+ 2 锆石εHf (t)）比南帕米尔岩基相对较多。帕米尔高原的晚白垩世岩浆作用在这里被解释为与新特提斯洋板回滚相关的伸展作用的结果，这与喀喇昆仑地体和科希斯坦地区类似年龄的伸展相关的岩浆作用是一致的。帕米尔高原在 42-36 Ma 处还有一个额外的岩浆脉冲，该脉冲受地理限制（约 150 公里直径的椭圆体区域），被称为 Vanj 岩浆杂岩。 Vanj 杂岩由准铝质、高 K 钙碱性到钾长岩二长岩、正长岩和埃达克质花岗岩（La/Yb N= 13 至 57）和低 Mg#(35–41) 组成。 Vanj 复合体显示出一系列 SiO 2 (54–75 wt.%) 和同位素组成（− 7 至− 3 εNd (i)、0.706 至 0.710 87 Sr/86 Sr (i)、− 3 至+ 1 锆石 εHf (i)、6.0 至 7.6‰ 锆石 δ 18 O VSMOW），这反映了一些幼年地幔输入以及随后与中/南帕米尔地体下地壳的同化或混合。据推测，Vanj 杂岩是印度-亚洲碰撞引发的地幔滴流或小型分层事件的结果。 Vanj岩浆杂岩的年龄、地球化学、露头格局和构造位置表明，它是横跨帕米尔高原和西藏羌塘地体北部的一系列岩浆杂岩的一部分，绵延超过2500公里。所有这些杂岩都位于塔尼马斯-金沙缝合带的正南，这是印度-亚洲碰撞后重要的岩石圈和流变边界，集中了地幔岩石圈变形。帕米尔高原的中新世岩浆作用（20-10Ma）包括：1）同位素演化的混合岩和淡色花岗岩，与伸展片麻岩穹顶内的地壳锐斜和减压熔融有关； 2）邓凯尔迪克/塔克斯库尔干复合体的局部大陆内岩浆作用。
New geochronologic, geochemical, and isotopic data for Mesozoic to Cenozoic igneous rocks and detrital minerals from the Pamir Mountains help to distinguish major regional magmatic episodes and constrain the tectonic evolution of the Pamir orogenic system. After final accretion of the Central and South Pamir terranes during the Late Triassic to Early Jurassic, the Pamir was largely amagmatic until the emplacement of the intermediate (SiO 2> 60 wt.%), calc-alkaline, and isotopically evolved (− 13 to− 5 zircon εHf (t)) South Pamir batholith between 120–100 Ma, which is the most volumetrically significant magmatic complex in the Pamir and includes a high flux magmatic event at∼ 105 Ma. The South Pamir batholith is interpreted as the northern (inboard) equivalent of the Cretaceous Karakoram batholith and the along-strike equivalent of an Early Cretaceous magmatic belt in the northern Lhasa terrane in Tibet. The northern Lhasa terrane is characterized by a similar high-flux event at∼ 110 Ma. Migration of continental arc magmatism into the South Pamir terrane during the mid-Cretaceous is interpreted to reflect northward directed, low-angle to flat-slab subduction of the Neo-Tethyan oceanic lithosphere. Late Cretaceous magmatism (80–70 Ma) in the Pamir is scarce, but concentrated in the Central and northern South Pamir terranes where it is comparatively more mafic (SiO 2< 60 wt.%), alkaline, and isotopically juvenile (− 2 to+ 2 zircon εHf (t)) than the South Pamir batholith. Late Cretaceous magmatism in the Pamir is interpreted here to be the result of extension associated with roll-back of the Neotethyan oceanic slab, which is consistent with similarly aged extension-related magmatism in the Karakoram terrane and Kohistan. There is an additional pulse of magmatism in the Pamir at 42–36 Ma that is geographically restricted (∼ 150 km diameter ellipsoidal area) and referred to as the Vanj magmatic complex. The Vanj complex comprises metaluminous, high-K calc-alkaline to shoshonitic monzonite, syenite, and granite that is adakitic (La/Yb N= 13 to 57) with low Mg#(35–41). The Vanj complex displays a range of SiO 2 (54–75 wt.%) and isotopic compositions (− 7 to− 3 εNd (i), 0.706 to 0.710 87 Sr/86 Sr (i),− 3 to+ 1 zircon εHf (i), 6.0 to 7.6‰ zircon δ 18 O VSMOW), which reflects some juvenile mantle input and subsequent assimilation or mixing with the Central/South Pamir terrane lower crust. The Vanj complex is speculatively interpreted to be the consequence of a mantle drip or small delamination event that was induced by India–Asia collision. The age, geochemistry, outcrop pattern, and tectonic position of the Vanj magmatic complex suggest that it is part of a series of magmatic complexes that extend for> 2500 km across the Pamir and northern Qiangtang terrane in Tibet. All of these complexes are located directly south of the Tanymas–Jinsha suture zone, an important lithospheric and rheological boundary that focused mantle lithosphere deformation after India–Asia collision. Miocene magmatism (20–10 Ma) in the Pamir includes: 1) isotopically evolved migmatite and leucogranite related to crustal anataxis and decompression melting within extensional gneiss domes, and; 2) localized intra-continental magmatism in the Dunkeldik/Taxkorgan complex.