From ocean depths to mountain tops: Uplift of the Troodos ophiolite (Cyprus) constrained by low‐temperature thermochronology and geomorphic analysis

Abstract

The timing and mode of uplift of the Troodos ophiolite are constrained by low-temperature thermochronology combined with geomorphic analysis. Zircon (U-Th)/He and apatite fission track cooling ages in the Troodos plutonic sequence are all Cretaceous (83-106 Ma) and within error of published zircon U-Pb crystallization ages. This indicates early cooling of the oceanic crust and termination of spreading axis magmatism at~90 Ma. Apatite (U-Th)/He ages decrease with reconstructed crustal depths from~40 Ma near the top of the sheeted-dike complex to~4 Ma within the mantle sequence. A prominent inflection point in the age versus depth curve defines the bottom of the exhumed helium partial retention zone and records the onset of rapid exhumation of the main Troodos massif at 6 ± 2 Ma. Inverse thermal modeling supports this conclusion, indicating that the timing of uplift is earlier than previously estimated. The boundaries of the mantle sequence exposed in the core of the Troodos structure closely overlap the boundaries of a concentric zone delineated by high local relief and higher channel steepness indices, indicating differential exhumation and uplift of this area relative to its surroundings. This zone also overlaps with a prominent negative Bouguer gravity anomaly. The timing and pattern of the Troodos ophiolite uplift suggest that it is driven by serpentinite diapirism, possibly triggered by Miocene reactivation of subduction along the Cyprean Arc. The worldwide ubiquity of suprasubduction zone ophiolites may thus reflect the importance of extensive serpentinization at the overthrusting mantle wedge in obduction processes.

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

“…Pale red symbols and black dotted lines indicate multiple intersections of individual samples due to sigmoidal shape of the Sr isotope seawater curve. Different columns indicate the magmatic and postmagmatic evolution of the Troodos SSZ (Avigad et al, ; Blome & Irwin, ; Bragina, ; Clube et al, ; Kinnaird et al, ; Morris et al, ; Mukasa & Ludden, ; Morag et al, ; Robertson, , ; Robertson et al, ; Robertson & Hudson, ; Robertson et al, ). Furthermore, 87 Sr/ 86 Sr reference ratios are given for published upper pillow lava‐hosted secondary calcites (Coogan et al, ; Gillis et al, ; Gillis & Robinson, ; Staudigel & Gillis, ; Weinzierl et al, ), pillow lavas (Bickle & Teagle, ; Chapman & Spooner, ; Gillis et al, ; Kawahata & Scott, ; McCulloch & Cameron, ; Peterman et al, ; Rautenschlein et al, ; Rommel & Friedrichsen, ; Spooner et al, ; Woelki et al, ), and umbers (Ravizza et al, ).…”

“…Intersection ages (Figure ) interpreted as the time of vein calcite precipitation and relative ages are consistent for a ~23 Ma old low‐T seawater‐derived late‐stage calcite from an incompletely sealed syntaxial analcime vein that crosscuts an ~85 Ma old low‐T blocky calcite vein (Figure d). This Early Miocene age falls into the temporal framework of minor Troodos uplift to hemipelagic or shallow water depth (Figure ; Avigad et al, ; Kinnaird et al, ; Morag et al, ; Robertson et al, ; Robertson et al, ). In a previous study, the formation of palygorskite and gypsum veins were also related to ophiolite emplacement (Gillis & Robinson, ).…”

“…The reactivation of oceanic subduction delivered water into the mantle causing serpentine diapirism and initiated the collision with the Eratosthenes seamount (Robertson, 1977(Robertson, , 1998. As a consequence, minor uplift from Late Oligocene to Early/Middle Miocene focusing on southern Troodos and major uplift in Pleistocene times took place (Kinnaird et al, 2011;Main et al, 2016;Morag et al, 2016;Robertson, 1977Robertson, , 1998Robertson et al, 2012). This domal uplift resulted in an annular outcrop pattern in which pillow lavas and sheeted dykes envelope plutonic rocks involving plagiogranites and gabbros, as well as serpentinized harzburgites and dunites (Bagnall, 1960;Bear, 1960;Bear & Morel, 1960;Carr & Bear, 1960;Gass, 1960;Gass & Masson-Smith, 1963;Wilson & Ingham, 1959; Figure 1).…”

“…Several N-S striking 10.1029/2019GC008369 Geochemistry, Geophysics, Geosystems normal faults run through the Margi area but are older than the maximum ages of micrite and antitaxial vein calcites (Boyle & Robertson, 1984). Instead, Troodos microplate rotation from Campanian to Early Eocene (Clube et al, 1985;Morris et al, 1990) and/or subduction reactivation and minor uplift in Late Oligocene to Early/Middle Miocene (Kinnaird et al, 2011;Main et al, 2016;Morag et al, 2016;Robertson, 1977Robertson, , 1998Robertson et al, 2012) might have triggered fracturing of the pillow lavas and overlying sediments. The proposed temporal framework for the formation of antitaxial calcite veins and associated micrites overlaps with both phases.…”

“…Sr/ 86 Sr ratios of vein calcites range from 0.70608 to 0.70833 ( Figure 5; Quandt et al, 2019). Syntaxial and UPL-hosted blocky vein calcites including spatially associated micrites cluster around 0.70732 and 0.70751 (Avigad et al, 2016;Blome & Irwin, 1985;Bragina, 2008;Clube et al, 1985;Kinnaird et al, 2011;Morris et al, 1990;Mukasa & Ludden, 1987;Morag et al, 2016;Robertson, 1977Robertson, , 1998Robertson et al, 1991;Robertson & Hudson, 1974;Robertson et al, 2012). Furthermore, 87 Sr/ 86 Sr reference ratios are given for published upper pillow lava-hosted secondary calcites (Coogan et al, 2019;Gillis et al, 2015;Gillis & Robinson, 1990;Staudigel & Gillis, 1990;Weinzierl et al, 2018), pillow lavas (Bickle & Teagle, 1992;Gillis et al, 2015;Kawahata & Scott, 1990;Peterman et al, 1971;Rautenschlein et al, 1985;Rommel & Friedrichsen, 1987;Spooner et al, 1977;Woelki et al, 2018), and umbers (Ravizza et al, 1999).…”