Role of magma mixing in generating of the Gheshlagh–Aftabrow intrusions, SW Buin Zahra, Iran: Evidence for a juvenile origin from geochemical and Sr–Nd isotopic data
Role of magma mixing in generating of the Gheshlagh–Aftabrow intrusions, SW Buin Zahra, Iran: Evidence for a juvenile origin from geochemical and Sr–Nd isotopic data
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DOI：
10.1002/gj.3384
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发表时间：
2018-12
影响因子：
1.8
通讯作者：
K. Kazemi;A. Kananian;Yilin Xiao;F. Sarjoughian
中科院分区：
文献类型：
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作者：
K. Kazemi;A. Kananian;Yilin Xiao;F. Sarjoughian
在本文中，我们研究了主花岗闪长岩和相关的镁铁质微粒包体（MME），包括来自中始新世 Gheshlagh-Aftabrow 花岗岩的辉长岩到石英闪长岩包体，以评估 Urumieh-Dokhtar 岩浆弧中的岩浆混合和壳幔相互作用。主体花岗闪长岩产生的锆石 U-Pb 年龄约为 100。 40马。地球化学和块体岩石 Nd-Sr 同位素模拟，以及广泛出现的具有椭圆形和球形形状和冷缘的镁铁质微粒包体，包体中存在钾长石和斜长石巨晶，以及具有振荡分带和吸收表面的针状磷灰石、眼状石英、斜长石的存在，表明镁铁质微粒包体是源自地幔的镁铁质岩浆球，被注入并与源自下地壳部分熔融的岩浆混合/混合。从地球化学角度看，花岗岩类岩石为高钾钙碱性和准铝质岩石（A/CNK=0.87~0.92），属于I型岩系。这些花岗岩类围岩的 SiO2 含量较高（65.4~67.3 wt%），而 Fe2O3（1.8~2.1 wt%）和 MgO（1~1.58 wt%）相对较低，因此与围岩相比，镁铁质微粒包体的 SiO2 含量要低得多（50.5~55 wt%），而 Fe2O3 含量要高得多（3.4~4.2 wt%）。 wt%）和 MgO（3.9–4.8 wt%）。相对于 HREE，宿主侵入体和飞地都富集了 LREE（LREE/HREE = 3.1–4.1；(La/Yb)N = 2.1–4.1），并显示出轻微的负 Eu 异常（δEu = 0.75–0.90）和几乎平坦的 HREE 模式（（Gd/Yb）N = 0.86–1.26）。对宿主花岗闪长岩和相关飞地中的 Sr-Nd 同位素分析显示，(87Sr/86Sr)i 宿主 = 0.705070–0.705174，εNd(t) 宿主 = 0.21–2.31，TDM1 宿主 = 782–983 Ma，(87Sr/86Sr)i 飞地 = 0.704997–0.705170，εNd(t) 包体 = 2.15–2.17，TDM1 包体 = 874–980 Ma，表明这些花岗岩具有幼年性质。这一特征与类似的微量元素成分一起表明了强烈的岩浆混合以及宿主花岗闪长岩与其包体之间的高度地球化学平衡。
In this paper, we investigate host granodiorites and associated mafic microgranular enclaves (MMEs), including gabbroic to quartz diorite enclaves from the Middle Eocene Gheshlagh–Aftabrow granitoid, to assess magma mixing and crust–mantle interaction in the Urumieh–Dokhtar magmatic arc. The host granodiorites yield zircon U–Pb ages of ca. 40 Ma. Geochemical and bulk rock Nd–Sr isotopic modelling, together with the widespread occurrence of mafic microgranular enclaves with ellipsoidal and spherical shapes and chilled margins, K‐feldspar and plagioclase megacrysts in the enclaves, and the presence of acicular apatite, ocellar quartz, plagioclase with oscillatory zoning and resorption surfaces, suggests that the mafic microgranular enclaves are globules of a more mafic magma derived from the mantle that was injected into and mixed/mingled with the magma derived from partial melting of a lower crust. Geochemically, the granitoid rocks are high‐K calc‐alkaline and metaluminous (A/CNK = 0.87–0.92) and belong to I‐type suite. These granitoid host rocks have much higher SiO2 (65.4–67.3 wt%) and relatively low Fe2O3 (1.8–2.1 wt%) and MgO (1–1.58 wt%), so compared with the host rocks, the mafic microgranular enclaves have much lower SiO2 contents (50.5–55 wt%), considerably higher Fe2O3 (3.4–4.2 wt%) and MgO (3.9–4.8 wt%). Both the host intrusion and enclaves are enriched in LREE relative to HREEs (LREE/HREE = 3.1–4.1; (La/Yb)N = 2.1–4.1) and show slightly negative Eu anomalies (δEu = 0.75–0.90) and nearly flat HREE patterns ((Gd/Yb)N = 0.86–1.26). Analyses of Sr–Nd isotopes in the host granodiorites and associated enclaves show (87Sr/86Sr)i host = 0.705070–0.705174, εNd(t) host = 0.21–2.31, TDM1 host = 782–983 Ma, (87Sr/86Sr)i enclave = 0.704997–0.705170, εNd(t) enclave = 2.15–2.17, and TDM1 enclave = 874–980 Ma, indicating of juvenile nature for these granites. This characteristic together with similar trace‐element compositions indicates intense magma mixing and a high degree of geochemical equilibration between the host granodiorites and their enclaves.