ABSTRACT

The SE segment of the Urumieh-Dokhtar Magmatic Belt (UDMB), known as Dehaj-Sarduieh Magmatic Belt, includes a huge pile of Palaeogene volcano-sedimentary rocks and Eocene to Miocene mafic to felsic intrusions. In the middle of this belt (in Raviz-Shanabad, W Rafsanjan) mafic-intermediate intrusions (as stocks and/or dikes-sills) are abundant and have intruded into the volcano-sedimentary rocks of Dehaj-Sarduieh. The thickness of dikes range from 0.5 to >5 metres and the minimum diameter of the intrusions is ~10 m. These rocks are highly porphyritic and have gabbroic to dioritic composition. Petrographic data indicate that the main rock-forming minerals include plagioclase (labradorite to anorthite based on the new electron microprobe data), pyroxene (augite), and opaque (magnetite and titanomagnetite) minerals, set in a granular groundmass of the same minerals. New zircon U-Pb data show that the age of these rocks is 34.39 ± 0.31 Ma (Late Eocene). These rocks show calc-alkaline characteristics and their geochemical signatures are compatible with arcs with a derivation from subduction zones. Estimated temperature and pressure from Clinopyroxene of these rocks suggest a temperature in the range of 1050° to 1150°C and a pressure of >2 kbar. These data show the formation depth of these intrusions should be ~18 km. Initial ⁸⁷Sr/⁸⁶Sr ratio for these rocks varies from 0.70403 to 0.70409, whereas ¹⁴³Nd/¹⁴⁴Nd isotope ratio changes between 0.5128 and 0.5129, corresponding to εNd(i) values of +3.5 to +6.6. These geochemical and isotopic evidences show that the melts originated by 5% partial melting of amphibole spinel peridotite mantle source. Petrographic observations as well as mineral chemistry and isotopic studies indicate that assimilation-fractional crystallization (AFC) has probably played a dominant role in the evolution of the Raviz-Shanabad intrusions. We suggest these intrusions formed as a part of the Late Eocene high-flux magmatism in SE segment of the UDMB in an active continental margin, which was related to the subduction of Neo-Tethys oceanic lithosphere beneath the Central Iranian microcontinent.

摘要

Urumieh-Dokhtar岩浆带（UDMB）的SE段，称为Dehaj-Sarduieh岩浆带，包括一大堆古近纪火山沉积岩和始新世至中新世镁铁质至长英质侵入。在该带的中部（位于拉夫桑詹的拉维兹-沙纳巴德），镁铁质中间侵入体（作为种群和/或堤坝基岩）丰富并且侵入了Dehaj-Sarduieh的火山沉积岩中。堤防的厚度范围从0.5到> 5米，侵入体的最小直径为〜10 m。这些岩石是高度斑状的，具有辉长岩至闪长岩的成分。岩石学数据表明，主要的成岩矿物包括斜长石（根据新的电子探针数据，拉长石到钙长石），辉石（辉石）和不透明（磁铁矿和钛磁铁矿）矿物，设置在相同矿物质的颗粒状地面中。新的锆石U-Pb数据显示这些岩石的年龄为34.39±0.31 Ma（晚始新世）。这些岩石表现出钙碱性特征，其地球化学特征与由俯冲带推导的弧线相容。这些岩石的斜辉石估计的温度和压力表明温度在1050°至1150°C的范围内，压力大于2 kbar。这些数据表明，这些侵入的形成深度应为〜18 km。最初的 这些岩石的斜辉石估计的温度和压力表明温度在1050°至1150°C的范围内，压力大于2 kbar。这些数据表明，这些侵入的地层深度应为〜18 km。最初的 这些岩石的斜辉石估计的温度和压力表明温度在1050°至1150°C的范围内，压力大于2 kbar。这些数据表明，这些侵入的形成深度应为〜18 km。最初的这些岩石的⁸⁷ Sr / ⁸⁶ Sr比从0.70403到0.70409，而¹⁴³ Nd / ¹⁴⁴Nd同位素比在0.5128至0.5129之间变化，对应于+3.5至+6.6的εNd（i）值。这些地球化学和同位素证据表明，这些熔体是由闪石尖晶石橄榄岩地幔源的5％局部融化引起的。岩石学观察以及矿物化学和同位素研究表明，同化-分形结晶（AFC）可能在Raviz-Shanabad侵入体的演化中起了主导作用。我们建议这些侵入是在活动大陆边缘UDMB SE段的晚始新世高通量岩浆作用的一部分，这与新特提斯海洋岩石圈在伊朗中部微大陆下方的俯冲有关。