Cenozoic Lamprophyres From <scp>NE</scp> Türkiye: New Constraints on Post‐Collisional Metasomatism and Alkaline Magma Origin in the Juvenile Subcontinental Lithospheric Mantle

ABSTRACT The Middle Eocene (~43 Ma) and Late Miocene (~6 Ma) lamprophyres cropping out as sills from NE Türkiye can be classified as alkaline lamprophyres. These lamprophyres exhibit moderate contents of K 2 O (2.22–2.59 and 2.58–2.98 wt%), K 2 O/Na 2 O ratios (0.78–1.14 and 0.62–0.94) and Mg# (40.55–46.32 and 56.93–61.52), respectively, and low concentrations of mantle compatible elements. The lamprophyres also have a moderate to relatively high abundance of rare earth elements (ΣREEs = 140–159 and 547–604 ppm, respectively) with significantly fractionated REE patterns (La N /Yb N = 6.82–9.10 and 65.17–71.31, respectively), and are enriched in large‐ion lithophile and light REEs but depleted in high‐field‐strength and heavy REEs. The lamprophyres have homogeneous and moderately low ( 87 Sr/ 86 Sr) i of 0.705048–0.705474 and 0.705252–0.705401, and nearly uniform εNd (i) values varying from −0.47 to 0.20 and 0.54 to 0.79 and εHf (i) values varying from 4.51–6.71 and 5.83–6.18, respectively. They also have a narrow and moderately high Δ7/4Pb range of 6.19–15.41 and 10.62–10.88 and Δ8/4Pb range of 49.56–56.14 and 46.86–47.99, respectively. Petrological modelling suggests that the parental magmas of both the Eocene and Miocene lamprophyres were generated by the low‐degree partial melting of phlogopite‐bearing spinel‐garnet and amphibole‐bearing garnet lherzolite sources, respectively. By integrating whole‐rock trace elements and isotope compositions with regional geological observations, we propose that the post‐collisional Middle Eocene and Late Miocene lamprophyres in the Eastern Pontides Orogenic Belt originated from the juvenile subcontinental lithospheric mantle sources metasomatized initially by Neotethyan subduction‐related fluids during the Eocene, and subsequently overprinted by delaminated lithosphere‐derived carbonate components in the Miocene. The lamprophyres likely record a temporal magmatic response to lithospheric delamination and regional thermal upwelling associated with Eocene extensional tectonics, followed by lithospheric thinning during the Miocene in a post‐collisional tectonic setting.