![]() 2016) and minimizes the influence of an Afar plume although, several authors have argued for Afar plume importance for western Arabia volcanism based on geochemical constraints (e.g., Murcia et al. ![]() The petrology of volcanism along the SRS, the NRS and in the vicinity of the MMTZ supports the model of passive rifting for the Red Sea (Konrad et al. 2014) it began along the SRS at ~ 28 Ma with activity continuing until 15 Ma (Bosworth and Stockli 2016). Volcanism began along the Sirhan rift at 28 Ma and continued until 22 Ma (Segev et al. Pre-rift volcanism in the vicinity of the Afar commenced at ~ 40 Ma, with maximum eruption rates at 30 Ma when rifting initiated (Wolfenden et al. Here we describe the evidence supporting this model of plate boundary evolution, test the process numerically using finite element methods, and discuss some of the insights into early-stage plate boundary formation provided by the MMTZ. Its tectonic activity since abandonment provides additional insight into the nature of an early stage lithospheric-scale plate boundary structure. Because of this abandonment, the MMTZ has preserved many of the characteristics of an early-stage rift-to-rift continental transform. The MMTZ and Sirhan were abandoned contemporaneously (23 Ma) with a major dike-intrusion event (Boone et al. This lithospheric-scale structure, across western Arabia, appears to have been initiated at ~ 30–28 Ma based on the volcanic activities along two active rifting margins, the southern Red Sea (SRS) and the Sirhan rift. In this paper, we call the structure bounding this extensional region on the south the Makkah–Madinah Transform Zone (MMTZ). ![]() This region of diffuse extension predates the MMN volcanic line, since the region includes older diffuse grabens and dike intrusions (Roobol and Stewart 2009). It should be noted that the extension rates today in this broad zone, outside the main NRS rift, are low (Aldaajani et al. 2008), and to the south by a localized volcanic activities along a lineament termed the Makkah–Madinah–Nafud (MMN) volcanic line (Camp and Roobol 1992). The NRS extensional zone is bounded to the east by the Sirhan Rift (Roobol and Stewart 2009), to the west by the Egyptian western dessert (Stockli and Bosworth 2019), to the north by the Mediterranean oceanic lithosphere (Erduran et al. The region of northern Red Sea (NRS) diffuse extension extends beyond the Red Sea itself, and is seen in the form of dikes, grabens, and ongoing volcanism outside the rift zone. 1), with the northern diffuse extension considered to involve relatively symmetrical crustal stretching (Hosny and Nyblade 2016). 2015) and northern diffuse extensional styles (Roobol and Stewart 2009) (Fig. The early Red Sea rift is characterized by differing southern localized (Almalki et al. Over time, with continued seafloor spreading, the two sides of the continental lithosphere bounding this initial transform become displaced from each other, complicating attempts to document the processes associated with formation and initial motion along the transform (e.g., Swanson 1982). In some cases, the specific rift segments that evolve into the successful localized spreading centers may be significantly offset from each other, producing a continental rift–transform–rift structure that, with continued extension, may evolve into a large-offset ridge–transform–ridge structure such as the Romanche transform (e.g., Bonatti et al. The transition to the present tectonic setting suggests an ephemeral rift–rift–transform triple junction within the central Red Sea connecting the localized southern Red Sea rift, a developing northern Red Sea rift, and the MMTZ transform.ĭuring the early stages of continental breakup, prior to the development of a fully formed mid-ocean ridge, a broad zone of extension may form (e.g., Wilson and Guiraud 1992). The Sirhan Rift and the MMTZ connection to the Red Sea spreading center was mostly abandoned with the development of the Dead Sea fault, and localization of extension in the present-day northern Red Sea. During this time, the MMTZ served as a primary lithospheric-scale boundary between the Arabia and Nubia plates. It connected the more evolved southern Red Sea mid-ocean ridge to the initially dominant Sirhan Rift. We find that the Makkah–Madinah Transform Zone (MMTZ) represents a rift-to-rift continental transform fault that served as a primary component of the initial plate boundary between Arabia and Nubia. The recent occurrence of this rifting and the multi-stage evolution of the plate boundary has preserved of key components of the early-stage plate boundary development. The continental-rifting of Arabia from Nubia, and the initial evolution of the Red Sea spreading center includes many of the continental-rifting to ocean-spreading processes, in particular transform formation, and the eventual development of a mid-ocean ridge.
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