Early Oligocene Continental Alkalibasalts of the Central Toveireh Area (Southwest of Jandaq, Isfahan Province, Iran)
Early Oligocene Continental Alkalibasalts of the Central Toveireh Area (Southwest of Jandaq, Isfahan Province, Iran)
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DOI：
10.1134/s001685212202011x
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发表时间：
2022-04
期刊：
影响因子：
1.1
通讯作者：
H. Salim;G. Torabi;N. Shirdashtzadeh;M. Sahlabadi;T. Morishita
中科院分区：
文献类型：
--
作者：
H. Salim;G. Torabi;N. Shirdashtzadeh;M. Sahlabadi;T. Morishita
早渐新世碱性玄武岩出露于伊朗伊斯法罕省扬达克市西南部、伊朗微大陆中东部西北部的托维雷中部地区。野外研究表明，这些碱性玄武岩横穿始新世钙碱性火山岩和花岗岩类，并被中新世沉积岩覆盖。玄武岩岩浆沿局部断裂上升到地表。根据岩相学分析，这些碱性玄武岩主要由橄榄石和斜长石等矿物组成，并有单斜辉石、辉石、铬尖晶石和磁铁矿等少量矿物。显微结构有斑状、微石斑状、粗面状、抗环斑状、冠状、筛状结构和斜长斑状结构。橄榄石的化学成分为镁橄榄石和镁橄榄石(FO0.90-0.75)，斜长石为拉斑岩-单斜长石(An63.1-20.7)，碱性长石为透辉石(50.3-61.5)，单斜辉石为透辉石和辉石(Mg#0.79-0.87)，铬尖晶石为斜方辉石(Cr#0.24-0.25)，尖晶石(Mg#0.72-0.76)在某些样品中以捕虏晶的形式存在。这些岩石中二氧化硅和二氧化钛的平均含量分别为48.96和1.54(wt%)。球粒陨石和原始地幔标准化图解的特征是轻稀土相对重稀土元素的相对富集，大分子稀土元素的富集，没有明显的Eu异常。霞石的标准含量高达14.6%。模式矿物学和规范矿物学以及矿物和全岩的地球化学数据表明，这些岩石是在俯冲停止后的板内大陆构造岩浆环境中形成的苏打-高苏打碱性玄武岩。全岩化学数据表明，中部Toveireh碱性玄武岩可能是由软流圈地幔中含有角闪石的石榴石二辉橄榄岩相对中等程度的部分熔融形成的，而软流圈地幔深度约105公里，以前曾因新特提亚板块的俯冲而富集。
The Early Oligocene alkalibasalts exposed in the Central Toveireh area located in the southwest of Jandaq city in Isfahan Province (Iran) and northwest of the Central-East Iranian Microcontinent (CEIM). Field studies reveal that these alkalibasalts crosscut the Eocene calc-alkaline volcanic rocks and granitoids and covered by the Miocene sedimentary rocks. The basaltic magma rose to the surface along the local faults. Based on the petrography, these alkalibasalts are composed of major minerals of olivine and plagioclase, and minor minerals of clinopyroxene, sanidine, Cr-spinel, and magnetite. The microscopic textures are porphyritic, microlithic porphyritic, trachytic, anti-rapakivi, corona, sieved texture, and poikilitic. Olivines are forsterite and chrysolite (Fo0.90–0.75), plagioclases are labradorite to oligoclase (An63.1–20.7), alkali-feldspars are sanidine (Or50.3–61.5), clinopyroxenes are diopside and augite (Mg# 0.79 to 0.87), and Cr-spinels are hercynite (Cr# 0.24 to 0.25) in chemical composition, spinels (Mg# 0.72 to 0.76) are present as xenocrysts in some samples. The average contents of SiO2and TiO2of these rocks are 48.96 and 1.54 (wt %), respectively. The chondrite and primitive mantle-normalized diagrams characterized by enriched LREE relative to HREE, LILE enrichment, and absence of evident Eu anomaly. The normative content of nepheline reaches up to 14.6%. Modal and normative mineralogy, as well as geochemical data of minerals and whole rocks revealed that these rocks are sodic to highly sodic alkalibasalts formed in a within-plate continental tectonomagmatic setting after the cessation of subduction. The whole-rock chemical data indicate that the Central Toveireh alkalibasalts probably formed by relatively medium degrees of partial melting of an amphibole-bearing garnet lherzolite from the asthenospheric mantle of about 105 km in depth, which was previously enriched by subduction of the Neo-Thetyan slab.