Magmatism associated with Gondwanaland rifting and Neo-Tethyan oceanic basin development: evidence from the Mamonia Complex, SW Cyprus

Volcanic and intrusive rocks of the Dhiarizos Group, occurring within the Mamonia Complex of SW Cyprus, comprise mainly tholeiitic basalts, ocean island tholeiites (OIT) and other alkalic varieties, with minor alkaline lamprophyre intrusive rocks. These rocks were highly tectonized and dismembered during the collision with the Troodos oceanic lithosphere. Trace element data for the most primitive mafic igneous rock samples suggest that the tholeiitic basalts are derived from a depleted mantle source whereas the OIT and the alkalic basalts originated from variable degrees of partial melting of a spinel peridotite mantle. Alkaline lamprophyres are products of a small degree of partial melting of a deep-seated garnet lherzolite. The bulk of the tholeiites and alkalic varieties are Late Triassic in age and are interpreted as having formed during Neo-Tethyan sea-floor spreading and associated seamount volcanism. Amphibole separates from a lamprophyre intrusion have ⁴⁰Ar–³⁹Ar ages of 140.7 ± 0.4 Ma. In this paper, we report for the first time an Early Cretaceous alkaline lamprophyric magmatism, which is probably associated with a renewed episode of Gondwanaland rifting. These results show that the development of the Neo-Tethyan oceanic basin in the Eastern Mediterranean was largely controlled by a two-phase rifting–drifting process.

出露于塞浦路斯西南部马莫尼亚杂岩（Mamonia Complex）内的迪亚里佐斯组（Dhiarizos Group）火山岩与侵入岩，主体由拉斑玄武岩（tholeiitic basalts）、洋岛拉斑玄武岩（ocean island tholeiites，OIT）及其他碱性岩类组成，伴生少量碱性煌斑岩侵入体。这些岩石在与特罗多斯海洋岩石圈（Troodos oceanic lithosphere）碰撞过程中发生强烈构造变形并被构造肢解。对最原始的镁铁质火成岩样品的微量元素数据研究表明，拉斑玄武岩源自亏损地幔源，而洋岛拉斑玄武岩与碱性玄武岩则形成于尖晶石橄榄岩地幔的不同程度部分熔融。碱性煌斑岩是深部石榴石二辉橄榄岩（garnet lherzolite）低度部分熔融的产物。绝大多数拉斑玄武岩与碱性岩类形成于晚三叠世，被认为是新特提斯洋海底扩张及伴随的海山火山作用的产物。对一处煌斑岩侵入体的角闪石单矿物分离相开展的⁴⁰Ar–³⁹Ar年龄测试结果为140.7 ± 0.4 Ma。本文首次报道了早白垩世碱性煌斑岩岩浆作用，该作用可能与冈瓦纳大陆新一轮裂谷事件相关。上述研究结果显示，东地中海地区新特提斯洋盆的演化主要受控于两阶段裂谷-漂移过程。