南喀尔巴阡山脉(罗马尼亚)西Getic基底具有阿达基期特征的华力西前花岗质岩石:基于全岩和锆石地球化学的成因和时间限制

IF 1.3 4区 地球科学 Q2 GEOLOGY Geologica Acta Pub Date : 2021-04-14 DOI:10.1344/GEOLOGICAACTA2021.19.4
A. Dobrescu
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引用次数: 0

摘要

通过对南喀尔巴阡山脉(Semenic Mountains)西域Slatina-Timis (STG)和Buchin (BG)两个类地层侵入岩的研究,发现了大陆碰撞环境下具有埃达质特征的花岗岩类。高Na 2o、Al 2o3和Sr、贫Y(40)、(La/Yb) N (bbb10)比值、无Eu异常的全岩地球化学组成与高硅埃达奇岩(HSA)的主要特征重合,但存在Mg#较低、重金属含量较低、87 Sr/ 86 Sr比值略高的差异。玄武岩源实验表明,与HSA相比,tonalite - trondhjemite - grano闪长岩(TTG)岩石和熔体在超过125 gpa的压力和800-900℃的温度下(经ti -锆石计算温度证实)部分熔融是主要的成因过程,残留石榴石角闪岩、石榴石麻粒岩或榴辉岩类型。在STG-BG岩石中观测到的阿达质特征和地球化学变化表明,洋源熔体受到地幔影响增加和地壳输入减少的影响,这可能将构造背景限制在低角度俯冲条件下的板块熔化。另一种模式认为,STG-BG岩浆的成因与60-50km地壳深度的榴辉岩和石榴石角闪岩的部分熔融有关,这是在同步俯冲发掘榴辉岩化的板块碎片和地幔堆积过程中发生的。花岗岩类在碰撞过程中被卷入浮力混杂岩,并随机放置在两个大陆单元之间。LA-ICP-MS得到的U-Pb锆石年龄被解释为奥陶系火成岩结晶时间和瓦里斯坎再结晶印记,并通过锆石测年带的微量元素特征加以证实,将STG-BG岩浆活动与瓦里斯坎前俯冲碰撞事件联系起来。丰富的锆石继承揭示了新元古代幼锆石和以新太古代至古元古代锆石为代表的较古老的地壳成分。
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Pre-Variscan granitoids with adakitic signature at west Getic basement of the South Carpathians (Romania): constraints on genesis and timing based on whole-rock and zircon geochemistry
Research on two strata-like intrusions from Slatina-Timis (STG) and Buchin (BG) at West Getic Domain of the South Carpathians (Semenic Mountains) identified granitoids with adakitic signature in a continental collision environment. Whole-rock geochemical composition with high Na 2 O, Al 2 O 3 and Sr, depleted Y ( 40), (La/Yb) N (>10) ratios and no Eu anomalies overlaps the High-Silica Adakites (HSA) main characteristics, though there are differences related to lower Mg#, heavy metal contents and slightly increased 87 Sr/ 86 Sr ratios. Comparison with HSA, Tonalite-Trondhjemite-Granodiorite (TTG) rocks and melts from experiments on basaltic sources suggests partial melting at pressures exceeding 1.25GPa and temperatures of 800-900oC (confirmed by calculated Ti-in zircon temperatures) as the main genetic process, leaving residues of garnet amphibolite, garnet granulite or eclogite type. The adakitic signature along with geochemical variations observed in the STG-BG rocks indicate oceanic source melts affected by increasing mantle influence and decreasing crustal input that may restrict the tectonic setting to slab melting during a subduction at low angle conditions. An alternative model relates the STG-BG magma genesis to garnet-amphibolite and eclogite partial melting due to decompression and heating at crustal depth of 60-50km during syn-subduction exhumation of eclogitized slab fragments and mantle cumulates. The granitoids were entrained into a buoyant melange during collision and placed randomly between two continental units. U-Pb zircon ages obtained by LA-ICP-MS and interpreted as Ordovician igneous crystallization time and Variscan recrystallization imprint are confirmed by trace-element characteristics of the dated zircon zones, connecting the STG-BG magmatism to a pre-Variscan subduction-collision event. The rich zircon inheritance reveals Neoproterozoic juvenile source and older crustal components represented by Neoarchean to Paleoproterozoic zircons.
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来源期刊
Geologica Acta
Geologica Acta 地学-地质学
CiteScore
2.50
自引率
6.70%
发文量
13
审稿时长
>12 weeks
期刊介绍: - Relevant conceptual developments in any area of the Earth Sciences. - Studies presenting regional synthesis. - Thematic issues or monographic volumes presenting the results from one or more research groups. - Short papers reflecting interesting results or works in progress. - Contributions and results from Research Projects, Workshops, Symposiums, Congresses and any relevant scientific activity related to Earth Sciences. - Geologica Acta aims to stimulate rapid diffusion of results and efficient exchange of ideas between the widespread communities of Earth Science researchers (with special emphasis on Latinamerica, the Caribbean, Europe, the Mediterranean
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