East Greenland 72-74° N Inland to Coast Thermo-tectonic Evolution Jensen, Peter K.; Hansen, Kirsten Publication date: 2018 Document version Publisher's PDF, also known as Version of record Document license: Unspecified Citation for published version (APA): Jensen, P. K., & Hansen, K. (2018). East Greenland 72-74° N Inland to Coast Thermo-tectonic Evolution. 130. Download date: 27. sep.. 2021 1. Igneous rocks and processes 1.1 Hotspots and intraplate signatures close to those of lithospheric wallrock materials. We suggest that, with the possible magmas: mantle sources, exception of very strongly enriched magma types, magmatic processes and the continental lithosphere has in many cases metasomatism. acted as a ‘pepper mill’, only spicing up CFB magmas otherwise predominantly generated in the sublithospheric mantle. ORAL The role of sublithospheric mantle ORAL sources in continental flood basalt magmatism: lessons learned from the Magmatism associated with Karoo LIP Gondwanaland rifting: Evidence from Iraq Zagros Suture Zone Jussi S. Heinonen1, Arto V. Luttinen2, Teal R. Riley3 and Sanni Turunen2 Sabah Ismail1 and Shaleer Burhan2 1Department of Geosciences and Geography, University 1Education college for pure sciences/Kirkuk of Helsinki, 2Finnish Museum of Natural History, University/Iraq, 2Applied Geology Department/Kirkuk University of Helsinki, 3British Antarctic Survey University/Iraq The role of sublithospheric mantle sources is The opening of the southern basin of the Neo- elusive in continental flood basalt (CFB) Tethys as a result of the breakup of Gondwana provinces. This is because on their way to the during Late Triassic was accompanied by the surface of the Earth, the parental magmas of CFBs eruption of flood basalts. This process led to the interact with thick continental lithosphere and fragmentation of continental lithosphere and may lose their primary geochemical rifting of these fragments from the northern characteristics. Several studies have also margin of Gondwana and created deep trench suggested that the predominant mantle sources grabens which were subsequently filled by of continental flood basalts are within the radiolarite deposits. Such events are well continental lithosphere. Our studies in the documented in southern Turkey, northwestern Antarctic and, more recently, African parts of the Syria and southwestern Cyprus. Fragments Early Jurassic Karoo LIP over the past 25 years related to these activities also exist as thrust have revealed the existence of several nappes in the Iraqi Zagros Suture Zone(Avroman sublithospheric mantle-derived magma types. platform limestone and Qulqula radiolarite)Such Their sources range from depleted upper mantle nappes also occur systematically beneath the (DM) to different kinds of enriched mantle (EM), obducted ophiolites from Greece to Oman. In the and possibly even to ancient primordial plume Iraqi Zagros Suture Zone the Late Triassic sources originating from the core-mantle Avroman nappe was thrusted over the Early boundary. Whereas the recognized EM sources Cretaceous Qulqula radiolarite and both were seem to be anomalous and had minor thrusted over the Late Cretaceous ophiolites. The contributions to Karoo magmatism, the DM and Avroman volcanics are lava flows consisting of primordial-like sources may have been very olivine-basalts, diabases, trachytes and tuffs. important in the generation of voluminous Karoo Previous K-Ar dating of a diabase rock gave an magmas. Energy-constrained assimilation‒ age of 220 Ma ± 20. Geochemical analysis of these fractional crystallization modeling has revealed rocks indicates that the alkali olivine basalts are that only a few percent of assimilation can shift strongly enriched in light rare earth elements the CFB trace element and radiogenic isotope without Eu anomalies. Trace element data for the 1 most primitive mafic igneous rock samples end-members: Two have Nb-depleted suggest that the tholeiitic basalts are derived compositions relative to primitive mantle, but from an enriched mantle source with OIB markedly different depleted and enriched signature formed within plate activity. This isotopic compositions. The third end-member is alkaline magmatism may have taken place as Nb-undepleted and shows isotopic affinity to continental flood basalts erupted during rifting of bulk silicate Earth. Three Karoo picrite suites can Gondwana at Norian with evidences of mantle be associated with these end-members, whereas plume interaction in the early rifting phase other picrites probably represent subordinate related to the opening of the Neo-Tethys. mantle components. In the Karoo province, the delta-Nb tracers pave the way for: (1) provincial scale mapping of ORAL mantle heterogeneity using variably contaminated flood basalts and (2) identification Tracing of mantle heterogeneity in of picrites best suited for geochemical Karoo flood basalts using Nb-Zr-Ti-Y characterisation of the major mantle ratios components. Arto Luttinen1, Sanni Turunen1 and Jussi Heinonen2 1Finnish Museum of Natural History, P.O. Box 44, 00014 ORAL University of Helsinki, Finland, 2Department of Geosciences and Geography, P.O. Box 64, 00014 Assessing primary vs. secondary University of Helsinki, Finland geochemical fingerprints of Icelandic basalts using high-Fo# olivine The study of mantle sources of continental flood crystals basalt provinces is often compromised by crustal Maja B. Rasmussen1, Sæmundur A. Halldórsson1, contamination overprinting of the incompatible Martin J. Whitehouse2, Sally A. Gibson3 and David element and isotopic ratios of the predominant R. Hilton4 rock types. Geochemical tracers which are 1Nordic Volcanological Center, University of Iceland, unaffected by contamination help to: (1) identify Reykjavik, Iceland, 2Swedish Museum of Natural co-genetic types of flood basalts, (2) establish History, Stockholm, Sweden, 3University of Cambridge, parent-daughter relationships between flood Cambridge, UK, 4Scripps Institution of Oceanography, basalt types and rare uncontaminated picrites, UCSD, La Jolla, USA and (3) constrain mantle source heterogeneity even when picrite types are unknown. Identification of such tracers has turned out to be Oxygen isotope ratios (d18O) of Icelandic basalts difficult, however. are notably distinct from MORB-sourced basalts. Two prevailing hypotheses have been put We have examined variations of Nb/Y, Nb/Zr, and forward to account for this: interaction with low- Nb/Ti at given Zr/Y (quantified d18O crust or mantle heterogeneity [1]. High-Fo# using ΔNbY, ΔNbZr and ΔNbTi) in geochemically olivine crystals are widely used as a proxy for diverse Karoo flood basalts. Importantly, the primary melt composition prior to crustal delta-Nb values are only mildly affected by modification [2]. Therefore, their geochemical melting, crystallisation, and contamination characteristics can be useful to determine the processes and can be used as tracers of mantle source of low-d18O in Icelandic basalts. We couple source heterogeneity. in-situ d18O of high-Fo# (>80) olivine crystals from the neovolcanic rift- and flank zones as well In the Karoo province, the variations as older Tertiary units with major and trace in ΔNb , ΔNb , and ΔNb and initial Nd and Sr Y Zr Ti elements using SIMS, EMPA and LA ICPMS as isotopic ratios call for at least three mantle source tools to identify primary vs. secondary controls 2 on some notable geochemical characteristics of lavas in the Luenha river area, Central Icelandic basalts. Mozambique, reveal a third significant mantle source for Karoo basalts. The olivine crystals show limited intra-grain variability but, collectively, they display a The Luenha picrites differ from other Karoo 18 variation in d O(Ol) of >3 ‰ across Iceland, with picrites based on their high positive ΔNb values most values falling below the expected depleted (+0.5 to +0.6), low Ti contents, and low Zr/Y. mantle-value (~5.1 ±0.2‰ [3]). The lowest Variable initial 87Sr/86Sr and incompatible trace 18 d O(Ol) (+2.77 ‰), is measured in crystals from element ratios likely result from mild crustal central Iceland, close to the inferred plume head contamination. A single picrite sample lacks [4]. Trace element ratios of these olivine crystals indications of contamination and indicates a (e.g., Mn/Fe) suggest a peridotitic mantle source, mantle source with 87Sr/86Sr of 0.7041 and εNd of implying a shallow (likely crustal) origin of the +2 and an overall geochemical affinity to a 18 low d O(Ol). In contrast, crystals from the South primitive or mildly depleted mantle. We maintain Iceland Volcanic Zone display trace element that this magma source may represent the ratios indicative of greater amount of pyroxenite previously unknown mantle component which is 18 in their source region while their d O(Ol) vary required to explain the high abundance of Karoo significantly (from +3.45 to +4.98 ‰). These low-Ti basalts with positive ΔNb. Bearing in mind results, together with previously published that several large igneous provinces (e.g. Ontong 3He/4He values for these same samples [4], imply Java) have been recently associated with melting a regional shift in the dominating mantle of geochemically primitive mantle type plume lithology and plumbing conditions beneath heads, the Luenha picrites may provide a unique Iceland. geochemical insight into a major plume source previously inferred from geophysical studies of the Karoo province. ORAL Luenha picrites reveal a primitive ORAL mantle type plume source in the Karoo large igneous province?