Abstract Triassic rift-related volcanic rocks outcrop over all mainland Greece, comprising of trachybasalts and basaltic trachyandesites. Relatively immobile to the effects of alteration processes major and trace element abundances classify the volcanics into OIB and E-MORB lavas. They have mainly been distinguished based upon their: i) LREE contents, ii) silica-saturation index (S·I.), iii) Zr/Nb and Nb/Y ratio values; iv) Th, U, and Ta contents v) geotectonic discrimination diagrams. Their geochemistry indicates that most rocks were affected by moderate to extensive differentiation processes, mostly expressed by clinopyroxene fractionation. Some of the OIB and E-MORB volcanics are considered as primitive undersaturated, displaying low SiO2, Zr/Nb and S·I. values and also high Mg# and CaO/Al2O3 and La/Nb ratios. Calculated average mantle potential temperatures are comparable (1410 °C OIB; 1370 °C E-MORB), with melt fractions estimated at 3–5% for primary OIB magmas and 6–8% for primary E-MORB magmas. An asthenospheric origin is inferred for the OIB lavas, with melting in the garnet stability field (75–95 km; 2.5–3.0 GPa), whereas E-MORB parent magmas were formed with melting in the garnet/spinel (transitional) stability field (55–70 km; 1.8–2.2 GPa). The Hellenic Triassic rift-related lavas were most likely generated and erupted after lithospheric attenuation and extension, followed by subsequent asthenospheric upwelling of the mantle. The high calculated partial melting degrees and the observed thick and voluminous lava formations account for fast-spreading of the Tethys ridge during the Triassic. Temperature results indicate that the Hellenic Triassic rift-related magmas were generated from mantle at ambient temperature, precluding a mantle plume-based scenario or of significant thermal anomalies.

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与希腊三叠纪裂谷相关的熔岩起源和形成的岩石成因限制

摘要 三叠纪裂谷相关火山岩在整个希腊大陆上露头，包括粗面玄武岩和玄武质粗面岩。相对不受蚀变过程影响的主要和微量元素丰度将火山岩分为 OIB 和 E-MORB 熔岩。它们的区别主要基于它们的：i) LREE 含量，ii) 二氧化硅饱和指数 (S·I.)，iii) Zr/Nb 和 Nb/Y 比值；iv) Th、U 和 Ta 含量 v) 大地构造区分图。它们的地球化学表明，大多数岩石受到中度到广泛的分异过程的影响，主要表现为单斜辉石分馏。一些 OIB 和 E-MORB 火山岩被认为是原始欠饱和的，显示出低 SiO2、Zr/Nb 和 S·I。值以及高 Mg# 和 CaO/Al2O3 和 La/Nb 比率。计算出的平均地幔位温相当（1410 °C OIB；1370 °C E-MORB），估计原生 OIB 岩浆的熔体分数为 3-5%，估计原生 E-MORB 岩浆的熔体分数为 6-8%。推断 OIB 熔岩为软流圈起源，在石榴石稳定场（75-95 公里；2.5-3.0 GPa）中熔化，而 E-MORB 母岩浆是在石榴石/尖晶石（过渡）稳定场中熔化形成的（ 55–70 公里；1.8–2.2 GPa）。与希腊三叠纪裂谷相关的熔岩很可能是在岩石圈衰减和伸展之后产生和喷发的，随后是地幔软流圈上涌。计算出的高部分熔融度和观察到的厚而庞大的熔岩地层是三叠纪期间特提斯洋脊快速扩张的原因。