Facies architecture, geochemistry and petrogenesis of Middle Triassic volcaniclastic deposits of Mt. Ivanščica (NW Croatia): evidence of bimodal volcanism in the Alpine-Dinaridic transitional zone

IF 1.8 2区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Duje Smirčić, Matija Vukovski, Damir Slovenec, Duje Kukoč, Branimir Šegvić, Marija Horvat, Mirko Belak, Tonći Grgasović, Luka Badurina
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引用次数: 0

Abstract

During the Middle Triassic, intensive volcanic activity took place along the eastern margin of Pangea, including the Greater Adria promontory, due to the Neotethyan oceanization. This resulted in the formation of various volcanic and volcaniclastic rock types. The region of NW Croatia, acting as a transition zone between the Southern Alps and the Dinarides, showcases the outcrops of these rocks. The present study investigates the facies of volcaniclastic rocks, the distribution of those facies, formation processes, as well as the genesis of the primary magma to gain a better understanding of the complex geodynamics of this region during the Middle Triassic. Six profiles across the Vudelja quarry front were surveyed using drone imaging and samples were collected for detailed petrographic and geochemical analyses. Two groups of volcaniclastic rocks were identified—mafic and intermediate/felsic. The former is represented by (I) autoclastic effusive facies and (II) resedimented autoclastic facies, while the latter is represented by (III) secondary pyroclastic facies. Mafic volcaniclastics were generated through basaltic effusions in marine environments, fragmentation in contact with seawater, mixing with shallow marine carbonate clasts, and subsequent redeposition in deeper marine areas. The secondary pyroclastic facies (III) consists of a regionally distributed felsic Pietra Verde tuff whose deposits may be related to pyroclastic density currents and syn-eruptive resedimentation by turbidite-like currents. Geochemical data indicate that parental magmas responsible for generating the mafic volcaniclastics had a calc-alkaline composition and originated in ensialic and mature arc settings of an active continental margin. The observed chemical composition is likely inherited from older, arc-related lithologies, associated with the subduction of the Paleotethys Ocean. Parental magmas are thought to have formed during continental rifting of the passive Middle Triassic margins of the Greater Adria through (i) partial melting of the heterogeneous lithospheric mantle, which had been metasomatized during an earlier Hercynian subduction, and (ii) subordinate processes related to the melting of the upper continental crust and subsequent fractionation. Ar/Ar dating on plagioclase separates yielded an age of 244.5 ± 2.8 Ma for mafic volcaniclastics. This aligns well with biostratigraphic ages of felsic tuffs which crop out on a broader regional scale of the Dinarides, the Southern Alps, and the Transdanubian Range. The overlapping ages obtained from radiometric dating of mafic volcaniclastics and biostratigraphic ages of the felsic Pietra Verde tuffs strongly suggest that the Greater Adria region experienced concurrent bimodal volcanism during the Middle Triassic.
伊万希察山(克罗地亚西北部)中三叠纪火山碎屑沉积物的面貌结构、地球化学和岩石成因:阿尔卑斯-第纳尔过渡带双峰火山活动的证据
在中三叠世,由于新近纪的大洋化,潘加大陆东缘(包括大阿德里亚海角)发生了密集的火山活动。这导致了各种火山岩和火山碎屑岩的形成。克罗地亚西北部地区是南阿尔卑斯山和迪纳利山脉之间的过渡地带,展示了这些岩石的露头。本研究调查了火山碎屑岩的岩相、这些岩相的分布、形成过程以及原生岩浆的成因,以便更好地了解该地区中三叠世期间复杂的地球动力学。利用无人机成像技术对 Vudelja 采石场前沿的六个剖面进行了勘测,并采集了样品进行详细的岩石学和地球化学分析。确定了两组火山碎屑岩--黑云母岩和中长岩。前者以(I)自爆喷出面和(II)再沉积自爆面为代表,后者以(III)次生火成岩面为代表。黑云母火山碎屑岩是在海洋环境中通过玄武岩喷出、与海水接触碎裂、与浅海碳酸盐碎屑混合,然后在深海区域重新沉积而形成的。次生火成岩面(III)由区域分布的长英质 Pietra Verde 凝灰岩组成,其沉积可能与火成岩密度流和浊积岩样流的同步爆发再沉积有关。地球化学数据表明,产生黑云母火山碎屑的母岩浆具有钙碱性成分,起源于活跃大陆边缘的英仙岩和成熟弧环境。所观察到的化学成分很可能是从较古老的、与弧有关的岩性中继承下来的,与古特提斯洋的俯冲有关。原生岩浆被认为是在大阿德里亚被动中三叠世边缘的大陆裂解过程中通过(i)异质岩石圈地幔的部分熔化和(ii)与上部大陆地壳熔化及随后的分馏有关的附属过程形成的。通过对斜长石分离物进行 Ar/Ar 测定,得出黑云母火山碎屑岩的年龄为 244.5 ± 2.8 Ma。这与在迪纳利山脉、南阿尔卑斯山脉和外多瑙河山脉等更大区域范围内出现的长岩凝灰岩的生物地层年龄十分吻合。通过对黑云母火山碎屑的放射性测年和对长石凝灰岩的生物地层学测年得出的重叠年龄有力地表明,大阿德里亚地区在中三叠世期间同时经历了双峰火山活动。
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来源期刊
Swiss Journal of Geosciences
Swiss Journal of Geosciences 地学-地质学
CiteScore
4.50
自引率
12.90%
发文量
21
审稿时长
>12 weeks
期刊介绍: The Swiss Journal of Geosciences publishes original research and review articles, with a particular focus on the evolution of the Tethys realm and the Alpine/Himalayan orogen. By consolidating the former Eclogae Geologicae Helvetiae and Swiss Bulletin of Mineralogy and Petrology, this international journal covers all disciplines of the solid Earth Sciences, including their practical applications. The journal gives preference to articles that are of wide interest to the international research community, while at the same time recognising the importance of documenting high-quality geoscientific data in a regional context, including the occasional publication of maps.
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