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"name": "Age and mantle sources of Quaternary basalts associated with \u201cleaky\u201d transform faults of the migrating Anatolia-Arabia-Africa triple junction",
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"value": "10.1130/GES02266.1",
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"@type": "Periodical",
"name": "Geosphere",
"volumeNumber": "17",
"issueNumber": "1"
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"datePublished": "2021",
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"abstract": "The Anatolia (Eurasia), Arabia, and Africa tec\u00adtonic plates intersect in southeast Turkey, near the Gulf of \u0130skenderun, forming a tectonically active and unstable triple junction (the A3\u00a0triple junction). The plate boundaries are marked by broad zones of major, dominantly left-lateral transform faults including the East Anatolian fault zone (the Anato\u00adlia-Arabia boundary) and the Dead Sea fault zone (the Arabia-Africa boundary). Quaternary basalts occur locally within these \u201cleaky\u201d transform fault zones (similar to those observed within oceanic transform faults), providing evidence that mantle melting, basalt genesis, and eruption are linked to crustal deformation and faulting that extends into the upper mantle. We investigated samples of alkaline basalt (including basanite) from the Toprakkale and Karasu volcanic fields within a broad zone of transtension associated with these plate-boundary faults near the \u0130skenderun and Amik Basins, respectively.Toprakkale basalts and basanites have\u00a040Ar/39Ar plateau ages ranging from 810 \u00b1 60 ka to 46 \u00b1 13 ka, and Karasu volcanic field basalts have\u00a040Ar/39Ar plateau ages ranging from 2.63 \u00b1 0.17 Ma to 52 \u00b1 16 ka. Two basanite samples within the Toprak\u00adkale volcanic field have isotopic characteristics of a depleted mantle source, with\u00a087Sr/86Sr of 0.703070 and 0.703136,\u00a0143Nd/144Nd of 0.512931 and 0.512893,\u00a0176Hf/177Hf of 0.283019 and 0.282995,\u00a0206Pb/204Pb of 19.087 and 19.155, and\u00a0208Pb/204Pb of 38.861 and 38.915. The\u00a0176Hf/177Hf ratios of Toprakkale basalts (0.282966\u20130.283019) are more radiogenic than Karasu basalts (0.282837\u20130.282965), with some overlap in\u00a0143Nd/144Nd ratios (0.512781\u20130.512866 vs. 0.512648\u20130.512806). Toprakkale\u00a0206Pb/204Pb ratios (19.025 \u00b1 0.001) exhibit less variation than that observed for Karasu basalts (18.800\u201319.324), and\u00a0208Pb/204Pb values for Toprakkale basalts (38.978\u2013 39.103) are slightly lower than values for Karasu basalts (39.100\u201339.219). Melting depths estimated for the basalts from both volcanic fields gener\u00adally cluster between 60 and 70 km, whereas the basanites record melting depths of ~90 km. Depth estimates for the basalts largely correspond to the base of a thin lithosphere (~60 km) observed by seismic imaging. We interpret the combined radio\u00adgenic isotope data (Sr, Nd, Hf, Pb) from all alkaline basalts to reflect partial melting at the base of the lithospheric mantle. In contrast, seismic imaging indicates a much thicker (>100 km) lithosphere beneath southern Anatolia, a substantial part of which is likely subducted African lithosphere. This thicker lithosphere is adjacent to the surface loca\u00adtions of the basanites. Thus, the greater melting depths inferred for the basanites may include par\u00adtial melt contributions either from the lithospheric mantle of the attached and subducting African (Cyprean) slab, or from partial melting of detached blocks that foundered due to convective removal of the Anatolian lithosphere and that subsequently melted at ~90 km depth within the asthenosphere.The Quaternary basalts studied here are restricted to a broad zone of transtension formed in response to the development of the A3\u00a0triple junction, with an earliest erupted age of 2.63 Ma. This indicates that the triple junction was well established by this time. While the current posi\u00adtion of the A3\u00a0triple junction is near the Amik Basin, faults and topographic expressions indicate that inception of the triple junction began as early as 5 Ma in a position farther to the northeast of the erupted basalts. Therefore, the position of the A3\u00a0triple junction appears to have migrated to the southwest since the beginning of the Pliocene as the Anatolia-Africa plate boundary has adjusted to extrusion (tectonic escape) of the Anatolia plate. Establishment of the triple junction over the past 5 m.y. was synchronous with rollback of the Afri\u00adcan slab beneath Anatolia and associated trench retreat, consistent with Pliocene uplift in Cyprus and with the current positions of plate boundaries. The A3\u00a0triple junction is considered to be unstable and likely to continue migrating to the southwest for the foreseeable geologic future.",
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