The Elat/Timna area in Southern Israel provides an unparalleled opportunity for geological field studies due to its unique geology, spanning from the Neoproterozoic to the Holocene. The well-exposed rocks document the variability and evolution of three major processes: the creation of the Arabian-Nubian Shield during the Neoproterozoic, the accumulation of the Cambrian to Eocene sedimentary sequence, and the Miocene to Recent evolution of the Dead Sea Transform, an active plate boundary. The area's geological diversity and extensive documentation of its geology have made it a particularly important study site for geoscience students. Recently the Geological Survey of Israel published new 1:50,000 scale geological maps of the area, updated by additional fieldwork and presented in a series of reports. This paper presents a brief geological overview and a description of six key locations, complete with maps and photos that are a showcase document to the area's geological uniqueness as an excellently-exposed window into 800 million years of Neoproterozoic to Holocene evolution at the NE African plate.

The Geological Survey of Israel (GSI) was founded in 1948 with the establishment of the State of Israel. Over the years, changes of the research directions were dictated by national needs as the population grew from less than 1 million to more than 9 million in 2020 in a small country of only 22,000 km(2) with highly diverse geological features. This was associated with a change in the structure of the survey and establishing it as a key player in sustainable development and effective utilization of natural resources. It became possible by the upgrade of the staff levels and the research facilities after the survey was recognized as an independent research institute by the government. The achievement of the GSI as an applied science organization in response to the country's ever-developing challenges is going hand in hand with becoming an international geo-scientific recognized organization.

The sinistral displacement along the Dead Sea Transform (DST), the plate boundary between the African and the Arabian plates, south of the Dead Sea basin, was previously attributed to two main fault zones: the Arava/Araba or Dead Sea fault and the Feinan or Al Quwayra fault zone. This was based on similarities of features on either side of the Araba Valley. In particular, the Timna and the Feinan copper mines, located north of the Themed and Dana faults, and the onlap of the Cambrian formations southward onto the Amram rhyolite and Ahyamir volcanics. To these we add a more accurate offset indicator in the form of an offset Early Cambrian (532 Ma) dolerite dyke previously mapped in Mount Amram (Israel) on the African plate and recently discovered across the Araba Valley in Jabal Sumr al Tayyiba (southwest Jordan) on the Arabian plate. This dolerite dyke is ~ 20 m thick, strikes N50°E and is the only dyke intruding the Jabal Sumr al Tayyiba pink rhyolite flows of the Ahyamir Volcanics. Geochemical and geochronological correlations between the Jabal Sumr al Tayyiba dolerite dyke and the Mount Amram dolerite dyke demonstrate 85 km of sinistral offset across the Arava/Araba fault. Our results also suggest approximately 109 km of combined sinistral displacement across the Arava/Araba and Feinan faults based on petrological correlations between the Timna and Jabal Hanna igneous complexes on the African and Arabian plates, respectively. This constrains the total sinistral displacement of the Feinan fault and its accessory faults to be 24 km.

The Mt Amram igneous complex (AIC) represents northern tip of the Neoproterozoic Arabian Nubian Shield (ANS). For the first time the AIC deep structure was studied using the gravity, aero and ground magnetic, magnetic susceptibility and density measurements and geological data. Analysing all available data at the Amram area we concluded what only monzonite body can be reason for gravity high and coinciding reduced to pole (RTP) maximum. Geological knowledge allowed suggesting its intrusive character and compact body form. Cluster of inverse solutions (Werner deconvolution) localized this body as initial model for forward modelling. Further iterations (23/4-D forward modelling) clarified the monzonite geometry and properties; the modelling allowed also to investigate the non-uniqueness and estimate also the confident intervals for final solution. The research consists three interconnected stages. At the detailed scale, ground magnetic data suggested three magmatic blocks of few hundred meters shifted dextral about 100 m along the Zefunut fault. Estimated accuracy for geometry of the magnetic bodies is a few tens metres. At the middle scale, quantitative gravity and magnetic interpretations provide model of the monzonite body, which is an order of magnitude more than the volume of the felsic rhyolites and granite rocks. Boundary of the whole monzonite body was estimated with accuracy as a hundred meters. As a result we suggest that the parent magma for the AIC is the monzonite, similar to the model suggested for the Timna Igneous Complex 12 km north of the AIC. The model developed can be applied to evaluate the subsurface volumes of the mafic magmatic rocks in adjacent locations. At the regional scale for exposed the Sinai and Arab Saudi Precambrian crystalline shield our approach allows to understand the apparent contradiction between geological predominantly granite composition (low magnetic rocks) and magnetic data. The aeromagnetic data show number strong magnetic anomalies suggesting the presence large volume of high magnetic (mainly basic) rocks at the depth. This problem is proposed for future research.

Recently, a detailed (1:50,000) geological map of the Elat area, southern Israel was published. Attached to this map is a stratigraphic table of the Neoproterozoic metamorphic magmatic complex of the study area. The Neoproterozoic basement in the Elat area encapsulates the Arabian Nubian Shield (ANS) geologic evolution. Uranium Lead and Lead Lead zircon ages, included in previous studies and referred to in this paper, reveal that these rocks were formed during more than 300 million years of Neoproterozoic time. The major process controlling the formation of the ANS as part of the East African Orogen is the closure of the Mozambique Ocean. The first orogenic phase in the Elat area, represented by the metamorphic rocks, includes the development of an island arc, erosion of the islands and deposition, and metamorphism. This event took place between similar to 950 Ma and 780-790 Ma. Elat Schist, the oldest metamorphic rock in the area, was deformed and then intruded by quartz dioritic and granitic plutons that were later deformed and metamorphosed. The amphibolite metamorphic rock fades indicate metamorphic conditions of up to 650 degrees C and between 4 and 5 kbar. The peak of the metamorphic event was most probably before 750 Ma. A gradual change from compressional to extensional stress regime is evidenced by emplacement andesitic magnesium-rich dykes dated to 705 Ma that were later metamorphosed to schistose dykes at a greenschist metamorphic facies. The second orogenic phase (terrane amalgamation, main shaping of crust) was associated with the emplacement of large volumes (>50% of area) of calc-alkaline intrusions in a post-collision setting. These very last stages of metamorphism and deformation are characterized by intrusion of similar to 630 Ma granitoids exhibiting some foliation. Pluton emplacement continued also after the end of deformation. Exhumation and transition to an extensional regime is recorded by the intrusion of shallow alkaline granites in similar to 608 Ma which were accompanied in similar to 609 Ma by rhyolite, andesite and composite dykes. The last magmatic event in the Elat area is represented by the volcano-conglomeratic series comprising rhyolites, basalts, andesites, hypabyssal intrusions of monzonite and syenite and conglomerates. The conglomerates, dated to about 590 Ma, are the products of a major erosion phase in which about 12,000 m of the section were removed. These conglomerates were intruded by 585 Ma rhyolite, andesite and composite dykes. The Neoproterozoic basement is truncated by a peneplain whose age, post 532 Ma, is constrained by the age of the youngest eroded dolerite dykes. This Early Cambrian peneplain was associated with erosion of 2000 m of the section and by chemical weathering. Three major breaks in Neoproterozoic magmatic activity are recognized: the first, occurred in Cryogenian time, lasted similar to 60 million years after the amphibolite facies metamorphism and before emplacement of the calc alkaline plutons, separating the first and the second orogenic phases; the second break between the orogenic and the extensional phases occurred in early Ediacaran time, encompassed similar to 20 million years between the emplacement of the calc-alkaline and alkaline plutonic rocks and rhyolite, andesite and the composite dykes; and the third, 50 Ma break, occurred between the emplacement of the last felsic intrusions at similar to 585 Ma and intrusion of the dolerite dykes in 532 Ma, before the Early Cambrian peneplain developed.The great lateral extension of the Cambrian to Eocene sedimentary rocks and their slow facies and thickness changes suggest a stable flat platform area at the northern tip of the ANS. Early Cambrian sedimentation began with fluviatile subarkoses of the Amudei Shlomo Formation. It was overlain by an Early to Middle Cambrian transgressive regressive lagoonal cycle of dolostones, sandstones, and siltstones of the Timna Formation. Then Middle Cambrian subarkoses and siltstones of the Shehoret Formation and the quartz arenite of the Netafim Formation were deposited in a coastal, intertidal environment representing the southern transgression of a Cambrian ocean. (C) 2014 Elsevier Ltd. All rights reserved.

The Dead Sea is a hypersaline terminal lake formed about 14,000 years ago along the central part of the Dead Sea Rift after the desiccation of its precursor Lake Lisan. The Dead Sea drains an area of approximately 40,000 km2 with the Jordan River as its main source of inflow (Fig. 12.1). While in the past the Dead Sea level changes were caused by climate changes, in recent years its level is controlled primarily by anthropogenic activity. At present the Dead Sea level is approximately 425 m below sea level (BSL) while the lake’s deepest point at 730 m BSL is the deepest terrestrial spot on Earth. This chapter summarizes the principal technical and environmental findings of the Red Sea-Dead Sea Conveyance Project. This is the main solution that is being currently discussed that can potentially resolve some of the issues the Dead Sea is facing.

Due to the increasing development of image spectroscopy techniques, airborne and spaceborne hyperspectral images have in recent years become readily available for use in geological applications. One of the prominent advantages of imaging spectroscopy is its high spectral resolution, producing detailed spectral information in each pixel. The current study aims at exploring the feasibility of the Earth-Observing-1 Hyperion imaging spectrometer to map the geology arena over the Dana Geology National Park, Jordan. After overcoming the common preprocessing difficulties (e.g., smile effect), a classification scheme of two levels was applied. The first level resulted in a stratigraphic classification product of eleven classes and the second level in a lithologic classification product of six classes. The overall accuracy of the stratigraphic product was 57%, while that of the lithologic product was 79%. Mismatches in classification were mostly related to terrestrial cover of the lower topography formation by rock and sand debris. In addition, low accuracy values can be attributed to Hyperion's high sensitivity, leading to recognition of different mineral compositions as different classes within a rock formation, while the conventional geology-stratigraphic map generalizes these different classes into one formation. The methods practiced in the current research can advance the Hyperion's classification capabilities and therefore can be applied in different geological settings and additional disciplines such as penology, agriculture, ecology, forestry, urban, and other environmental studies.

Abstract The Tambien Group of northern Ethiopia (Tigre), with probable correlatives in Eritrea, is a 2–3-km-thick siliciclastic–carbonate succession that was deposited in an intra-oceanic arc platform setting within the southern Arabian–Nubian Shield (ANS) area (southern extension of the Nakfa Terrane) of the Mozambique Ocean. Its deposition occurred prior to ocean closure between converging fragments of East and West Gondwana and concomitant structural emergence of the East African Orogen (EAO). The Tambien Group is well exposed and best studied in the Mai Kenetal and Negash synclinoria, where litho- and chemostratigraphy (including δ13Ccarb, 87Sr/86Sr) provide the basis for a composite reference section. Two glaciogenic intervals have been suggested from exposures within the Didikama and Matheos Formation in the Negash Synclinorium. No reliable palaeomagnetic data exist to constrain the palaeolatitude of Tambien Group deposition and the southern ANS, but palaeogeographic reconstructions and evaporite pseudomorphs in lower carbonate units (Didikama Formation) imply low to intermediate latitudes (<45°). Integration of available geochronological information (regional magmatism and detrital zircon) suggests c. 775–660 Ma as a plausible window constraining deposition of the prospective glacial intervals. The Tambien Group appears to preserve a coherent chemostratigraphic framework that can be effectively subdivided according to shifts in δ13Ccarb polarity [polarity intervals A (+), B (–), C (+), D (–)]. Slates underlying and interstratified with polarity interval A carbonate preserve evidence of extreme chemical weathering that lessened prior to deposition of polarity interval B carbonate. Tambien Group carbonate units have sedimentological characteristics consistent with both shallow and deeper marine depositional settings. The lower prospective glacial interval lacks diagnostic sedimentological evidence of synglacial deposition, but is overlain by negative δ13C carbonate (polarity interval B) with sedimentological characteristics consistent with well-documented cap-carbonate successions. The upper prospective glacial interval in the Negash Synclinorium (Matheos Diamictite) best exhibits characteristics consistent with glaciogenic deposition (matrix-supported polymictic clasts, possible dropstones, possible bullet-nosed and striated clasts). In contrast to pericratonic rift margin settings that are common for Cryogenian glaciogenic deposits, palaeogeographic reconstructions for the 775–660 Ma timeframe place northern Ethiopia within an intra-oceanic setting that was likely far removed from cratonic hinterlands. More work on Tambien Group sedimentology, geochronology and palaeogeography is required to better evaluate the extent and timing of glacial conditions associated with the prospective glaciogenic intervals. Supplementary material: Supplementary Table 21.1 of Tambien Group geochronological age constraints is available at http://www.geolsoc.org.uk/SUP18462.

Ethiopia's youngest Neoproterozoic sedimentary outcrops are "Sturtian" diamictites that cap the Tambien Group (Tigre, N. Ethiopia), a modestly thick (1–3 km) slate and carbonate succession that records early Cryogenian evolution of the Mozambique Ocean within the southern Arabian–Nubian Shield. Tambien carbonate deposition occurred over an island arc accretion complex, during or after the waning phase of arc magmatism (Tsaliet Group; ∼775–740 Ma) and ended prior to the structural and magmatic emergence of the East African Orogen (EAO; c. ≥630–610). Closure of the Mozambique Ocean to form the EAO, sometime after the deposition of "Sturtian" (∼715–685 Ma) diamictite and before the onset of EAO magmatism, destroyed accommodation space capable of preserving younger Cryogenian episodes. Litho- and chemostratigraphic variations of the Tambien Group, compiled from investigations of four areas of Tigre, demonstrate that integrated δ13Ccarb and 87Sr/86Sr stratigraphies are effective for regional correlation and form the basis for a composite reference section (introduced here, but evaluated in the context of evolving Cryogenian Earth systems in a companion manuscript). Sediments in the Negash synclinorium span the depositional histories of all other localities but may contain a significant unconformity, suggesting at least local structural relief differentiation during deposition of the early Tambien Group carbonate platform. Mai Kenetal synclinorium sediments may preserve this missing interval. The regional Tambien record has two consecutive positive-to-negative carbon isotope excursions, the first associated with an abrupt transition to carbonates with cap carbonate-like features (basal Assem Limestone - Mai Kenetal) and the second associated with the transition from relatively organic-rich black limestone to "Sturtian" diamictite (Negash). Sr isotope compositions rise from <0.7055 in dolomites near the base of the carbonate sequence to a stratigraphic plateau near 0.7068 in upper black limestones, before declining to 0.7064 (or lower) in the transition to diamictite deposition. Sr contents of limestones increase (9x) systematically above the lower negative δ13Ccarb interval. Textural and chemical properties of the Assem Limestone and its depositional context, suggest a transgressive cap-carbonate sequence. Although conformably underlain by laminated slate without definitive evidence of glaciation, its lithostratigraphic position as the lowest significant carbonate unit correlates regionally above polymict volcaniclastic agglomerates and greywackes (Negash and Samre synclinoria) previously interpreted to have a possible glacigenic origin. Chemical weathering indices (PIA: 92–99) in thick (0.5–1.1 km) slate comprising the lower Tambien Group indicate the Tsaliet arc accretion complex underwent protracted and intensive silicate weathering prior to carbonate deposition. These findings raise the possibility that the initial negative δ13Ccarb interval of the Tambien Group corresponds to recovery from an earlier pre-"Sturtian" cooling event, perhaps related to the Kaigas glacial interval. If so, the Assem Limestone is the first and oldest cap carbonate sequence in the Arabian–Nubian Shield. The chemostratigraphic framework for the Tambien Group contributes to empirical observations that integrated C and Sr isotope stratigraphies are effective for Cryogenian (pre-"Sturtian") chemostratigraphic correlations. However, more work is required to understand how δ13Ccarb specifically relates to marine δ13CDIC.

The similar to 450 million years of Neoproterozoic time (1000-542 Ma) was a remarkable episode of change in the Earth system and the biosphere. Here we develop and explore the hypothesis that explosive volcanism was at least partly responsible for Neoproterozoic climate change, synopsized as the "Volcanic winter to snowball Earth" (VW2SE) hypothesis. We review how climate cools as a result of sulfuric acid aerosols injected into the stratosphere by violent volcanic eruptions. A protracted increase in explosive volcanism could disrupt Earth's radiative balance by continuously injecting sulfur aerosols into the stratosphere, causing cooling that could lead to glaciation. This mechanism would be especially effective when acting in concert with other agents for cooling. We show that the global Neoproterozoic magmatic flux was intense, so that explosive volcanism episodicly had a major effect on climate. Neoproterozoic volcanism and glacial activity happened about the same times in the Cryogenian and Ediacaran periods with no glaciation and reduced igneous activity in the Tonian Period. Glaciation followed soon after igneous activity increased as the Supercontinent Rodinia broke apart, suggesting a causal relationship. The tectonic setting of climate-controlling explosive volcanism changed systematically over the Neoproterozoic supercontinent cycle, from extension-related early to arc-related late. Marinoan (similar to 635 Ma) glaciation in particular corresponds to a peak time of subduction-related igneous activity in the Arabian-Nubian Shield and the East African Orogen. Isotopic chemostratigraphies are generally consistent with VW2SE hypothesis. These observations cumulatively support the VW2SE hypothesis as a viable explanation for what solid Earth processes caused Neoproterozoic climate oscillations.

An EO-1 Hyperion scene was used to identify and map hydrothermally altered rocks and a Precambrian metamorphic sequence at and around the Alid volcanic dome, at the northern Danakil Depression, Eritrea. Mapping was coupled with laboratory analyses, including reflectance measurements, X-ray diffraction, and petrographic examination of selected rock samples. Thematic maps were compiled from the dataset, which was carefully pre-processed to evaluate and to correct interferences in the data. Despite the difficulties, lithological mapping using narrow spectral bands proved possible. A spectral signature attributed to ammonium was detected in the laboratory measurements of hydrothermally altered rocks from Alid. This was expressed as spectral absorption clues in the atmospherically corrected cube, at the known hydrothermally altered areas. The existence of ammonium in hydrothermally altered rocks within the Alid dome has been confirmed by previous studies. Spectral information of endmember's mineralogy found in the area (e.g. dolomite) enables a surface mineral map to be produced that stands in good agreement with the known geology along the overpass. These maps are the first hyperspectral overview of the surface mineralogy in this arid terrain and may be used as a base for future studies of remote areas such as the Danakil.

As a mega-project which will affect the environment, the feasibility of this project must be very thoroughly studied, especially the changing limnology of the Dead Sea. The amount of the desalinated water produced by this project might be significant for the region. The saved external sources of energy to produce drinking water in these projects is between 20% to 30%, only comparing to operation along the sea taking into account the pumping of the desalinated water to Amman and Hebron. The stratification and dilution of the Dead Sea water mass with seawater may cause losses for the Dead Sea Works and the Arab Potash Company, precipitation of gypsum and change the biological environment of the upper water mass.

Formation of the Arabian-Nubian Shield (ANS) and the East African Orogen (EAO) occurred between 870 Ma and the end of the Precambrian (similar to 542 Ma). ANS crustal growth encompassed a time of dramatic climatic change, articulated as the Snowball Earth hypothesis (SEH). SEH identifies tremendous paleoclimatic oscillations during Neoproterozoic time. Earth's climate shifted wildly, from times when much of our planet's surface was frozen to unusually warm episodes and back again. There is evidence for four principal icehouse episodes: similar to 585-582 Ma (Gaskiers), similar to 660-635 Ma (Marinoan), similar to 680-715 Ma (Sturtian), and similar to 735-770 Ma (Kaigas). Evidence consistent with the SEH has been found at many locations around the globe but is rarely reported from the ANS, in spite of the fact that this may be the largest tract of Neoproterozoic juvenile crust on the planet, and in spite of the fact that Huqf Group sediments in Oman, flanking the ANS, record evidence for Sturtian and Marinoan low-latitude glaciations. This review identifies the most important evidence preserved in sedimentary rocks elsewhere for SEH: diamictites, dropstones, cap carbonates, and banded iron formation (13117). Expected manifestations of SEH are integrated into our understanding of ANS and EAO tectonic evolution. If Kaigas and Sturtian events were global, sedimentary evidence should be preserved in ANS sequences, because these occurred during an embryonic stage of ANS evolution, when crustal components (island arcs, back-arc basins, and sedimentary basins) were mostly below sea level. Previous SEH investigations have been largely reconnaissance in scope, but potentially diagnostic sedimentary units such as diamictites, marine carbonates with 613 C excursions and banded iron formations are reported from the ANS and are worthy of further investigation. Collision and uplift to form the EAO destroyed most marine sedimentary basins about 630 Ma ago, so evidence of Marinoan and Gaskiers glaciations will be more difficult to identify. Several post-accretionary Neoproterozoic sedimentary basins in Arabia may preserve sedimentary evidence but such evidence has not been documented yet. The Huqf Group of Oman contains sedimentary evidence for the Marinoan glaciation but no evidence that the Gaskiers glaciation was significant in this part of the world. Deep erosion at similar to 600 Ma throughout the northern ANS and EAO may be related to Marinoan continental glaciation,. which may have accomplished much of the cutting of the ANS peneplain, but final shaping of the peneplain took place over the next 60 million years.African geoscientists can contribute to our understanding of Neoproterozoic climate change through careful field studies. and the international geoscientific community interested in Neoproterozoic climate change should pay attention to evidence from the ANS. Future investigations should include knowledge of the SEH and its controversial aspects, in addition to the greater plate tectonic setting of the ANS. (c) 2005 Elsevier Ltd. All rights reserved.

Detrital zircon geochronology of Neoproterozoic diamictites and Ordovician siliciclastics in northern Ethiopia reveals that the southern Arabian-Nubian Shield (ANS) formed in two major episodes. The earlier episode at 0.9-0.74 Ga represents island arc volcanism, whereas the later phase culminated at 0.62 Ga and comprised late to post orogenic granitoids related to crustal differentiation associated with thickening and orogeny accompanying Gondwana fusion. These magmatic episodes were separated by about similar to 100 my of reduced igneous activity (a magmatic lull is detected at about 0.69 Ga), during which subsidence and deposition of marine carbonates and mudrocks displaying Snowball-type C-isotope excursions (Tambien Group) occurred.Cryogenian diamictite interpreted as glacigenic (Negash synclinoria, Tigrai) and polymict conglomerates and arkose of possible peri-glacial origin (Shiraro area, west Tigrai), deformed and metamorphosed within the Ne oproterozoic orogenic edifice, occur at the top of the Tambien Group. They were formed well after the shutdown of island arc igneous activity in this region and are pierced by the post-collision granitoids. Negash diamictite and Shiraro sequence contain detrital zircons derived from underlying similar to 0.85-0.74 Ga volcanics, a small number of 1.1 Ga zircons (likely inherited within the underlying arc crust) were also detected. The youngest detrital zircons in these sequences are 0.75 and 0.74 Ga. A broadly Sturtian timing (i.e. similar to 0.70 Ga) is plausible, but we note this is a lower time limit. Our investigation shows that clasts in the diamictite have a proximal provenance and are derived from underlying igneous rocks and metasediments (including Tambien carbonates). Diamictites were formed when subsidence and basin sedimentation ceased and the Tambien and its underlying igneous complex (Tsaliet Group) were uplifted and eroded (incision exceeded 1500 m). Thus, although hearing the hallmark of a Snowball Earth, the properties of Tambien diamictites indicate relief differentiation and vertical motions may have played a significant role in shaping the glacial record of the southern ANS. (c) 2007 Elsevier B.V. All rights reserved.

The development of the Afar rift-rift-rift triple junction is analysed from the viewpoint of the Nubia, Arabia and Somali plate kinematics. A variety of constraints allow definition of a range of kinematic models that approximate well to the plate motions with a resolution of a couple to tens of kilometres. Rigid plate kinematics probably cannot resolve smaller motions. The size and location of the new area that opened between the major plates is inferred from plate kinematics and this provides a framework in which to assess the structural development that accommodates plate separation.The development of the Afar region was complicated by the presence of microplates - the Danakil and Aisha blocks - which results in a complex plate boundary geometry. This led to local deformation that does not directly reflect the divergence of the major plates, e.g. rotations of microplates and of minor blocks about vertical axes and strike-slip faulting. The opening of new area was accommodated by various crustal growth and accretion mechanisms, e.g. building of thick new igneous crust, normal seafloor spreading, and/or crustal stretching. Thus, plate motions by themselves do not determine the development of the plate boundaries, as this is strongly influenced by other factors such as lateral variations of the rates of magma supply (e.g. away from, and over, the Afar plume).The plate boundaries changed - e.g. the Gulf of Aden spreading centre propagated westward c. 2 Ma ago and normal seafloor spreading began along portions of the Red Sea axis since c. 5 Ma ago - while there were no resolvable changes in the plate motions. Such changes therefore signify a reorganization of the way in which plate divergence and addition of new area is accommodated: diffuse extension may give way to separation along a narrow spreading centre, or new plate boundaries may form at the expense of other boundaries that became inactive.