Provenance and magmatic-tectonic setting of Campanian-aged volcaniclastic sandstones of the Kannaviou Formation in western Cyprus: Evidence for a South-Neotethyan continental margin volcanic arc

Abstract

Regionally developed late Cretaceous subduction-related magmatism in the eastern Mediterranean records progressive closure of the Southern Neotethys. In western Cyprus the late Cretaceous (c. 90 Ma) Troodos ophiolite is depositionally overlain by volcaniclastic sandstones (up to 750 m thick) that are dominated by redeposited pyroclastic fallout, interbedded with both noncalcareous and calcareous radiolarian-bearing mudstones. The sands were mainly deposited by channelised mass flow processes and to a lesser extent by turbidity currents in a deep-water forearc basin. The succession was folded and locally thrust-deformed related to latest Cretaceous emplacement of adjacent Mesozoic continental margin and oceanic units (Mamonia Complex). SIMS U-Pb analysis of euhedral to subhedral magmatic zircon crystals yielded a weighted mean 206 Pb/ 238 U age of 80.1±1.1 Ma (Campanian). Sandstone petrography including compositional framework (Q12F21L67) suggests sediment supply from a volcanic arc. Subordinate continentally derived detritus suggests 2 a continental margin arc setting for the mafic to felsic fallout ash. SIMS analysis of little-altered volcanic glass indicates high Th/Nb and Th/La ratios that suggest the involvement of continental crust and/or subducted terrigenous sediments in magma genesis. Whole-rock chondrite-normalised REE patterns have comparable trends to modern and ancient forearc basin volcaniclastic sands and sandstones (e.g., northwest Pacific region). Trace element chemistry, although scattered towards the continental island arc fields on some geochemical diagrams (e.g., Th-Sc-Zr), mainly suggests an oceanic island arc source for the Kannaviou Formation sandstones, with variable enrichments in VCr -Ni-Sc, depletion in Nb-Ta, and relatively low trace element ratios (e.g., La/Co, Th/Co, La/Sc, Th/Sc). An explanation for this apparent discrepancy is that the volcaniclastic sandstones were derived from a relatively primitive arc constructed on previously depleted, rifted (thinned) Neotethyan continental crust. The inferred continental margin arc developed during early-stage northward subduction of Southern Neotethys beneath a Tauride microcontinent to the north. Large volumes of volcanic ash were derived from continental margin arc volcanism, probably in the vicinity of the Kyrenia Range in northern Cyprus.

Geochemistry of Vein Calcites Hosted in the Troodos Pillow Lavas and Their Implications for the Timing and Physicochemical Environment of Fracturing, Fluid Circulation, and Vein Mineral Growth

“…This secondary mineralization was dominated by low-T (<50°C) blocky and syntaxial vein calcites, which precipitated from pristine to slightly modified seawater under predominantly oxidizing redox conditions (Figure 9b). Together with Late Cretaceous sediment deposition on the seafloor (e.g., Chen & Robertson, 2019;Robertson, 1975Robertson, , 1977, these veins reduced the permeability of the oceanic crust within 10-20 Myr (~92-72 Ma) as indicated by intersections of 87 Sr/ 86 Sr ratios of samples with the Sr isotope seawater curve. These results are in accordance with and complement previously published studies that focused on the northern Troodos flank (Coogan et al, 2019;Gillis et al, 2015, and references therein;Gillis & Robinson, 1985Weinzierl et al, 2018).…”

“…Sedimentation of the Troodos pillow lavas initiated in the Turonian with the deposition of hydrothermal umbers (Bragina, 2008;Robertson, 1975). These are locally overlain by radiolarian mudstones, volcaniclastic sandstones, and claystones (Chen & Robertson, 2019;Robertson & Hudson, 1974). Area-wide deep-sea calcareous sediment deposition began in Maastrichtian (Robertson, 1977).…”

Identification of Forearc Sediments in the Milin-Zedong Region and Their Constraints on Tectonomagmatic Evolution of the Gangdese Arc, Southern Tibet

“…Therefore, the sediments collected from Milin-Zedong are probably dismembered blocks (e.g., [49]) derived/recycled from these units, that is, forearc sediments and passive margin sediment from the Himalayas or the Lhasa terrane. The characteristic zircon U-Pb-Hf features of these units in the Himalayan-Tibetan orogenic belt can undoubtedly shed light on the evolution of the Gangdese arc (e.g., [18,28]) and can provide information for the paleogeographic reconstruction of the Lhasa terrane [50] and for sedimentary provenancerelated studies of the surrounding basins [4,5,51].…”

“…However, only restricted exposures of the forearc sediments have been documented along the huge Gangdese plutonic belt (>1500 km long) [8], that is, mainly outcropping near and to the west of Xigaze. In contrast, no forearc sediments have been reported in the eastern part of the Gangdese arc (e.g., [4,5]). There are two possible explanations for this: either forearc sediments did not develop along this section of the arc or they developed but were destroyed during later orogenesis.…”

“…Forearc basins develop along convergent plate margins and receive detritus from the adjacent magmatic arc, and thus, they are important for studying the evolution of arcs [1][2][3][4][5]. The Xigaze forearc basin, located in the southern margin of the Lhasa terrane, southern Tibet, is one of the best exposed forearc basins in the world (e.g., [4,6]).…”