Mineralized fault zone parallel to the Oman ophiolite spreading axis

Smewing, J. D.; Simonian, K. O.; Elboushi, Ismail M.; Gass, I. G.

doi:10.1130/0091-7613(1977)5<534:mfzptt>2.0.co;2

Cited by 30 publications

(22 citation statements)

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“…The upper portion of the crustal section displays excellent preservation and exposures in the northern half of the ophiolite, and the largest massive sulphide deposits are also in the northern half of the ophiolite in the Lasail mining district ( Fig. 1): the Lasail, Bayda and Aarja deposits are all hosted within a NE-trending fault-bounded structure referred to as the 'Alley' by Smewing et al (1977). The ore deposits are confined to the boundary between the lowermost lavas (referred to as Geotimes, V1 or M1 by Alabaster et al (1982), Ernewein et al (1988) and Beurrier et al (1989), respectively) and the overlying lavas (referred to as Lasail, V2 or M2).…”

Section: Regional Settingmentioning

confidence: 98%

Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits

Stakes

Taylor

2003

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The extraordinarily well-preserved and well-exposed Semail ophiolite of northern Oman hosts several large plagiogranite intrusions in proximity to economic copper sulphide deposits of the Lasail mining district. A progression of isotopic, chemical and mineralogical transformations observed within the plagiogranites and high-level gabbros (HLG), and a comparison of these effects with those in the lowermost dykes of the immediately overlying sheeted dyke complex (SDC) tracks the evolution of hydrothermal fluids and the alteration of overlying dykes and pillow lavas during discharge of these fluids on the sea floor. The largest hydrothermal alteration aureoles, and the greatest extent of metamorphic veins and metasomatic replacement features, are found adjacent to the largest high-level plagiogranite bodies, beneath and adjacent to the major ore bodies in northern Oman. The ubiquitous presence of metamorphic actinolitic hornblende, sodic plagioclase, epidote and titanite in metabasalts within the high-temperature alteration zones points to the most likely mineralogical and structural controls on the development and evolution of the hydrothermal fluids. Depleted Cu contents of the adjacent crustal rocks and Cu enrichments above the plagiogranite intrusions demonstrate the redistribution of heavy metals adjacent to the complexes. Field relationships implicate the formation of both the epidosites and plagiogranites in the genesis of the ore deposits. An important process inferred from the field and geochemical data is the assimilation of previously hydrothermally altered basaltic and gabbroic country rocks by stoping into the magma chambers developed near the SDC-gabbro horizon in the ophiolite. We suggest that this process of combined assimilation-fractional crystallization, together with replenishment and recharge by injection and quenching of basaltic magma 'pillows' into these plagiogranite magma chambers (i.e. RAFC), plays a major role in the development of these composite intrusions.

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Section: Regional Settingmentioning

confidence: 98%

Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits

Stakes

Taylor

2003

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“…A genetic association between late dyke swarms, normal faulting, volcaniclastic breccias, boninitic volcanism, and VMS deposits has previously been noted for the "Bowling Alley" fault zone between Wadi Bani Umar and Wadi Kabiyat (Fizh block) and the nearby Aarja and Bayda VMS deposits (Gilgen et al, 2014;Haymon et al, 1989;Smewing et al, 1977). Early mapping viewed the fault zone as an eastfacing half graben that along its southern reach swings SW into Wadi Jizi (Smewing et al, 1977).…”

Section: Relationships Between Faulting Dyke Swarms Boninites and mentioning

confidence: 81%

Reply to referee Y. Kusano's comment

Belgrano¹

2019

Preprint

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Numerous studies have revealed genetic similarities between Tethyan ophiolites and oceanic "proto-arc" sequences formed above nascent subduction zones. The Semail ophiolite (Oman-U.A.E.) in particular can be viewed as an analogue for this proto-arc crust. Though proto-arc magmatism and the mechanisms of subduction initiation are of great interest, insight is difficult to gain from drilling and limited surface outcrops in marine settings. In contrast, the 3-5 km thick upper-crustal succession of the Semail ophiolite, which is exposed in an oblique cross section, presents an opportunity to assess the architecture and volumes of different volcanic rocks that form during the proto-arc stage. To determine the distribution of the volcanic rocks and to aid exploration for the volcanogenic massive sulfide (VMS) deposits that they host, we have remapped the volcanic units of the Semail ophiolite by integrating new field observations, geochemical analyses, and geophysical interpretations with preexisting geological maps. By linking the major-element compositions of the volcanic units to rock magnetic properties, we were able to use aeromagnetic data to infer the extension of each outcropping unit below sedimentary cover, resulting in a new map showing 2100 km 2 of upper-crustal bedrock.Whereas earlier maps distinguished two main volcanostratigraphic units, we have distinguished four, recording the progression from early spreading-axis basalts (Geotimes), through axial to off-axial depleted basalts (Lasail), to post-axial tholeiites (Tholeiitic Alley), and finally boninites (Boninitic Alley). Geotimes ("Phase 1") axial dykes and lavas make up ⇠ 55 vol % of the Semail upper crust, whereas post-axial ("Phase 2") lavas constitute the remaining ⇠ 45 vol % and ubiquitously cover the underlying axial crust. Highly depleted boninitic members of the Lasail unit locally occur within and directly atop the axial sequence, marking an earlier onset of boninitic magmatism than previously known for the ophiolite. The vast majority of the Semail boninites, however, belong to the Boninitic Alley unit and occur as discontinuous accumulations up to 2 km thick at the top of the ophiolite sequence and constitute ⇠ 15 vol % of the upper crust. The new map provides a basis for targeted exploration of the gold-bearing VMS deposits hosted by these boninites. The thickest boninite accumulations occur in the Fizh block, where magma ascent occurred along crustal-scale faults that are connected to shear zones in the underlying mantle rocks, which in turn are associated with economic chromitite deposits. Locating major boninite feeder zones may thus be an indirect means to explore for chromitites in the underlying mantle.

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“…The application of such a model to the Dalradian would imply that a northward-directed slip-zone existed and was active beneath the Dalradian basin in Lower Cambrian times similar to, or possibly a forerunner of, that which produced a subduction margin within the Southern Uplands in Lower Ordovician times, for which evidence is well documented (e.g. Similar deposits commonly occur at the base of the pillow lava unit in ophiolites (see Strong, 1974 a) in which deep-seated faults may have controlled the locus of upwelling of metal-bearing hydrothermal solutions during volcanism (Smewing et al 1977). While Harris et al (1978) noted the absence in the Dalradian of calc-alkaline volcanics and derived sediments which might be expected to be associated with such inferred subduction, several models could account for this absence.…”

Section: Basaltic Igneous Activity In the Scottish Dalradian 33mentioning

confidence: 95%

“…Phillips et al 1976;McKerrow, Leggett & Eales, 1977). The mass flow deposits and pillow-derived sediments which form from complex patterns of escarpments and basins in such fault zones (Smewing et al 1977) might be compared with the pillow lava turbidites, clastic and carbonate slump breccias and hyaloclastites recognized in the Loch Tay Limestone sequence above the Farragon Beds and below the Tayvallich Volcanics (Gower, 1977). We are not able to offer further evidence at this stage to discriminate between the above Atlantic-type and marginal basin models for the Dalradian igneous activity and sedimentation.…”

Section: Basaltic Igneous Activity In the Scottish Dalradian 33mentioning

confidence: 99%

Cambrian and late Precambrian basaltic igneous activity in the Scottish Dalradian: a review

Graham

Bradbury

1981

Geol. Mag.

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In the evolution of the Scottish Dalradian basin, the climax of widespread tholeiitic magmatism pie-dated or coincided with major basement faulting and the onset of deep marine sedimentation in Lower Cambrian times. Earlier basin-deepening and precursory igneous activity had already occurred. Major and trace element chemistry of low-grade metabasites indicates their affinity with basalts from ocean-spreading centres, or transition to ' within-plate' types. Geological evidence favours a tectonic setting for this igneous suite and the Highland Border Series on the NW margin of an actively evolving Lower Cambrian ocean basin, possibly a marginal basin to the Iapetus Ocean System.

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Mineralized fault zone parallel to the Oman ophiolite spreading axis

Cited by 30 publications

References 0 publications

Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits

Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits

Reply to referee Y. Kusano's comment

Cambrian and late Precambrian basaltic igneous activity in the Scottish Dalradian: a review

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