Abstract:Dykes or small stocks of plagiogranitic rocL· occur below the extrusive sequence and in mutually interpenetrating association with the sheeted dyke complex of the Evros Ophiolite, NE Greece. They are classified as tonalités, low silica trondhjemites (LST) and high silica trondhjemites (HST
“…Plagiogranite samples fall in the ORG field (Fig. 8c), overlapping the field of supra-subduction type Troodos plagiogranites, and plot close to Guevgueli trondhjemites and plagiogranite samples reported by Magganas (2007). Figure 8.Trace element discrimination diagrams for the plutonic rocks and mafic dykes.…”
“…Similarly, the petrology of analogous arc-related extrusive rocks in the Eastern Bulgarian Rhodope further supported their origin and tectono-magmatic setting (Bonev & Stampfli, 2008). In contrast, the only data available on the age, petrology and geochemistry of the intrusive section of the Evros ophiolites refer to the Middle Jurassic Petrota gabbros and associated leucocratic dykes (Biggazzi et al 1989;Frass et al 1990) or have been recently communicated (Bonev & Stampfli, 2005;Koglin et al 2007;Magganas, 2007). The lack of data on the intrusive rocks makes it difficult to establish the extent of the tectono-magmatic section and thus the significance of these ophiolites.…”
Section: Introductionmentioning
confidence: 89%
“…1990) or have been recently communicated (Bonev & Stampfli, 2005; Koglin et al . 2007; Magganas, 2007). The lack of data on the intrusive rocks makes it difficult to establish the extent of the tectono-magmatic section and thus the significance of these ophiolites.…”
-The incomplete Evros ophiolites in NE Greece form a NE−SW-oriented discontinuous belt in the Alpine orogen of the north Aegean. Field data, petrology and geochemistry are presented here for the intrusive section and associated mafic dykes of these ophiolites. Bodies of high-level isotropic gabbro and plagiogranite in the ophiolite suite are cross-cut by NE-SW-trending boninitic and tholeiitic-boninitic affinity dykes, respectively. The dykes fill tensile fractures or faults, which implies dyke emplacement in an extensional tectonic regime. The tholeiitic-transitional boninitic gabbro is REE-and HFS-depleted relative to N-MORB, indicating derivation from melting of a refractory mantle peridotite source. Associated boninitic dykes are slightly LREE-enriched, showing mineral and wholerock geochemistry similar to the gabbro. The plagiogranite is a strongly REE-enriched high-silica trondhjemite, with textures and composition typical for an oceanic crust differentiate. Plagiogranitehosted tholeiitic and transitional boninitic dykes are variably REE-enriched. Geochemical modelling indicates origin of the plagiogranite by up to 75 % fractional crystallization of basaltic magma similar to that producing the associated tholeiitic dykes. All mafic rocks have high LILE/HFSE ratios and negative Ta-Nb-Ti and Ce anomalies, typical for subduction zone-related settings. The mafic rocks show a similar trace-element character to the mafic lavas of an extrusive section in Bulgaria, suggesting they both form genetically related intrusive and extrusive suites of the Evros ophiolites. The field occurrence, the structural context, the petrology and geochemical signature of the studied magmatic assemblage provide evidence for its origin in a proto-arc (fore-arc) tectonic setting, thus tracing the early stages of the tectono-magmatic evolution of Jurassic arc-marginal basin system that has generated the supra-subduction type Evros ophiolites.
“…Plagiogranite samples fall in the ORG field (Fig. 8c), overlapping the field of supra-subduction type Troodos plagiogranites, and plot close to Guevgueli trondhjemites and plagiogranite samples reported by Magganas (2007). Figure 8.Trace element discrimination diagrams for the plutonic rocks and mafic dykes.…”
“…Similarly, the petrology of analogous arc-related extrusive rocks in the Eastern Bulgarian Rhodope further supported their origin and tectono-magmatic setting (Bonev & Stampfli, 2008). In contrast, the only data available on the age, petrology and geochemistry of the intrusive section of the Evros ophiolites refer to the Middle Jurassic Petrota gabbros and associated leucocratic dykes (Biggazzi et al 1989;Frass et al 1990) or have been recently communicated (Bonev & Stampfli, 2005;Koglin et al 2007;Magganas, 2007). The lack of data on the intrusive rocks makes it difficult to establish the extent of the tectono-magmatic section and thus the significance of these ophiolites.…”
Section: Introductionmentioning
confidence: 89%
“…1990) or have been recently communicated (Bonev & Stampfli, 2005; Koglin et al . 2007; Magganas, 2007). The lack of data on the intrusive rocks makes it difficult to establish the extent of the tectono-magmatic section and thus the significance of these ophiolites.…”
-The incomplete Evros ophiolites in NE Greece form a NE−SW-oriented discontinuous belt in the Alpine orogen of the north Aegean. Field data, petrology and geochemistry are presented here for the intrusive section and associated mafic dykes of these ophiolites. Bodies of high-level isotropic gabbro and plagiogranite in the ophiolite suite are cross-cut by NE-SW-trending boninitic and tholeiitic-boninitic affinity dykes, respectively. The dykes fill tensile fractures or faults, which implies dyke emplacement in an extensional tectonic regime. The tholeiitic-transitional boninitic gabbro is REE-and HFS-depleted relative to N-MORB, indicating derivation from melting of a refractory mantle peridotite source. Associated boninitic dykes are slightly LREE-enriched, showing mineral and wholerock geochemistry similar to the gabbro. The plagiogranite is a strongly REE-enriched high-silica trondhjemite, with textures and composition typical for an oceanic crust differentiate. Plagiogranitehosted tholeiitic and transitional boninitic dykes are variably REE-enriched. Geochemical modelling indicates origin of the plagiogranite by up to 75 % fractional crystallization of basaltic magma similar to that producing the associated tholeiitic dykes. All mafic rocks have high LILE/HFSE ratios and negative Ta-Nb-Ti and Ce anomalies, typical for subduction zone-related settings. The mafic rocks show a similar trace-element character to the mafic lavas of an extrusive section in Bulgaria, suggesting they both form genetically related intrusive and extrusive suites of the Evros ophiolites. The field occurrence, the structural context, the petrology and geochemical signature of the studied magmatic assemblage provide evidence for its origin in a proto-arc (fore-arc) tectonic setting, thus tracing the early stages of the tectono-magmatic evolution of Jurassic arc-marginal basin system that has generated the supra-subduction type Evros ophiolites.
“…9b) reveals enrichment of Large Ion Lithophile Elements (LILE) over High Field Strength Elements (HFSE). The most striking feature of the diagram is the depletion of Nb, Ti and P. These negative anomalies are likely to be related Cocherie (1978) and Magganas (2007). ORG -ocean ridge granite, VAG -volcanic arc granite, WPG -within plate granite, syn-COLG -syn-collisional granite.…”
Abstract:The Eldivan Ophiolite, exposed around Ankara and Çanklrl cities, is located at the central part of the I · zmirAnkara-Erzincan Suture Zone (IAESZ). It represents fragments of the Neotethyan Oceanic Lithosphere emplaced towards the south over the Gondwanian continent during the Albian time. It forms nearly complete series by including tectonites (harzburgites and rare dunites), cumulates (dunites, wherlites, pyroxenites, gabbro and plagiogranites) and sheeted dykes from bottom to top. Imbricated slices of volcanic-sedimentary series and discontinuous tectonic slices of ophiolitic metamorphic rocks are located at the base of tectonites. Plagiogranitic rocks of the Eldivan Ophiolite are mainly exposed at upper levels of cumulates. They are in the form of conformable layers within layered diorites and also dikes with variable thicknesses. Plagiogranites have granular texture and are mainly composed of quartz and plagioclases. The occurrences of chlorite and epidote revealed that these rocks underwent a low grade metamorphism. Eldivan plagiogranites have high SiO 2 content (70-75 %) and low K 2 O content (0.5-1 %) and display flat patterns of REE with variable negative Eu anomalies. LREE/HREE ratio of these rocks varies between 0.2-0.99. All members of the Eldivan rocks have high LILE/HFSE ratios with depletion of Nb, Ti and P similar to subduction related tectonic settings. Geochemical modelling indicates that the Eldivan plagiogranites could have been generated by 50-90 % fractional crystallization and/or 5-25 % partial melting of a hydrous basaltic magma.
“…Gabbroic rocks of subduction zone having ophiolite affinity might be the result of their formation in arc/back arc setting where extensional tectonism caused fracturing and dyke activity. Tholeiitic and boninitic dykes are common in many of ophiolite complexes of arc setting where they are considered as supra-subduction assemblage in marginal basin volcanic arc setting (Frass et al 1990;Magganas et al 1991;Magganas 2002Magganas , 2007Stampfli 2005, 2008).…”
Paharpur gabbroic intrusive is an arcuate body running east-west paralleling the foliation of Chhotanagpur Granite Gneiss which acts as country rock. The main gabbroic body is intruded by a number of dolerite dykes running north-south. It is composed of clinopyroxene (Wo 48 En 40 Fs 12-Wo 51 En 40 Fs 09 , mg no. 72-82), plagioclase (An 52-An 90), hornblende (magnesian hornblende to ferro-tschermackite), orthopyroxene (En 76-En 79) and ilmenite. Hornblende occurs as large poikilitic grain and constitutes around 60% of the rock. Both gabbro and associated dolerite dykes, show relatively primitive character (mg no. 65-73). Primitive mantle-normalized and MORB-normalized spider diagrams indicate enrichment in Rb, Ba, Th, La, Sr and depletion in Nb, Zr, Y, Ti and Nd. The LILE enrichment and Nb, Ti, Zr, Y depletion suggest arc like geochemical signature for the gabbroic and doleritic rocks of Paharpur. Flat to slightly LREE fractionated pattern and variable degree of REE enrichment is observed. An early stage fractionation of clinopyroxene, plagioclase, orthopyroxene, ilmenite and late stage reaction of cumulate pile and evolved melt/hydrous fluid is suggested for magmatic evolution of gabbro. Associated dolerite dykes, which are geochemically similar to the gabbro, have tholeiitic with boninitic character. The mineralogical and chemical compositions of intrusive rocks also have some similarity with mafic rocks of ophiolite complex of subduction zone.
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