Abstract A silica undersaturated alkali-olivine basanitic magma intruded the late Paleocene/early Eocene Jafnayn Formation near Muscat. Geochemical analyses indicate that a significant amount of host rock (limestone) was assimilated into the magma. We dated the basanite as 42.7 ± 1.0 Ma (2 sigma error; late Lutetian), using the whole rock 40Ar/39Ar step-wise heating technique. Intrusion occurred in the hanging wall of a major regional extensional shear zone (Frontal Range Fault, FRF) bounding the northern margin of two domes within the Oman Mountains (Jabal Akhdar and Saih Hatat domes). Two shear intervals along the FRF have been documented. The first interval lasted immediately after emplacement of the Semail Ophiolite (latest Cretaceous-early Eocene) while the second and poorly constrained interval was assumed to have occurred during the Oligocene. The proximity of the basanite to the FRF suggests that magma used extensional faults for the upper part of its ascent path. Reactivated Permian rift faults of the Pangaea rift or other preexisting faults may have been used for the lower ascent part. We conclude that the basanite intrusion coincided with the onset of the second deformation interval along the FRF, because (1) the position of the basanite is near a dextral releasing bend, associated with the second shear interval, (2) the overlap of our 40Ar/39Ar age with the cooling curves for rocks from the nearby Jabal Akhdar Dome, and (3) the basanite postdates the first FRF deformation episode by > 10 Ma. Thus, the second interval along the FRF had started already during the late Lutetian and probably lasted into the Miocene.

中文翻译：

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晚鹭田（始新世）基性侵入阿曼山脉（Rusayl Embayment）以北浅海台地沉积及其构造意义

摘要 一种二氧化硅不饱和碱橄榄石玄武岩岩浆侵入马斯喀特附近的晚古新世/早始新世Jafnayn组。地球化学分析表明，大量的主岩（石灰石）被同化到岩浆中。我们使用全岩 40Ar/39Ar 逐步加热技术将巴桑石定年为 42.7 ± 1.0 Ma（2 sigma 误差；Lutetian 晚期）。侵入发生在阿曼山脉内两个圆顶（Jabal Akhdar 和 Saih Hatat 圆顶）北缘的主要区域拉伸剪切带（Frontal Range Fault，FRF）的悬壁上。已经记录了沿 FRF 的两个剪切区间。第一个间隔在Semail蛇绿岩（最新的白垩纪-早始新世）就位后立即持续，而第二个和约束较差的间隔被认为发生在渐新世期间。巴桑岩与 FRF 的接近表明岩浆在其上升路径的上部使用了伸展断层。盘古裂谷重新活动的二叠纪裂谷断层或其他先前存在的断层可能已被用于较低的上升部分。我们得出结论，巴桑石侵入与沿 FRF 的第二变形区间的开始一致，因为（1）巴桑石的位置靠近与第二个剪切区间相关的右向释放弯曲，（2）我们的 40Ar /39Ar 年龄与附近 Jabal Akhdar Dome 岩石的冷却曲线，(3) 巴桑石比第一次 FRF 变形事件晚了 > 10 Ma。因此，沿 FRF 的第二个区间已经在卢特世晚期开始，并且可能持续到中新世。