Late Ediacaran syn‐rift/post‐rift transition and related fault‐driven hydrothermal systems in the Anti‐Atlas Mountains, Morocco

Abstract

The syn-rift/post-rift transition of the late Ediacaran-mid Cambrian Atlas rift is characterized by the interplay of several processes, such as a widespread episode of fracturing and tilting, associated with encasement of fault-controlled vein metallic ore deposits of economic importance, and carbonate production and phosphogenesis (Taguedit Bed, Tabia Member) bordering rift-flank uplifts. A correlatable unconformity marks the end of these processes and the beginning of a thermal subsidence-dominated regime with development of a more stable, carbonate, peritidal-dominated platform (Tifnout Member). Late Ediacaran microbial carbonate production and phosphogenesis extended in discontinuous belts around the periphery of uplifted rift shoulders and flanks. Karst development is interpreted to have formed along synsedimentary faults and fractures during abrupt tectonic uplift associated with emplacement of polymetallic hydrothermal dikes (rich in Cu, Fe and subsidiary Pb, Zn). Isotopic analysis indicates that speleothem precipitation in karstic palaeocaves displays significantly lighter d 13 C and d 18 O values as compared to the host dolomite, implying calcite precipitation by terrestrial fluids rich in decomposing organic matter and/or microbial activity in the cave system.

Geology and Metallogenesis of the Sediment-Hosted Cu-Ag Deposit of Tizert (Igherm Inlier, Anti-Atlas Copperbelt, Morocco)

“…In contrast, circulation of hydrothermal fluids during diagenesis would allow replacement of framboidal pyrite by Cu-sulphides and result in ore zone envelopes transgressive on lithologies. This is supported by the evolution from an environment dominated by regional block faulting during deposition of the Basal Series to an environment characterized by a thermal subsidence-dominated regime during deposition of the overlying Lower Limestone [43,59]. Accordingly the Lower Limestone of the Adoudou Formation was deposited on both the paleohighs and the depressions already filled by the Basal Series.…”

“…The normal faults, which affect the Basal Series, do not offset the Tamjout Dolomite and the overlying layered limestone, confirming that such extensional activity was contemporaneous with deposition of the Adoudou Formation. The transition from the clasticdominated formations of the Basal Series to the dolostonedominated formations of the Lower Limestone reflects the end of an environment with abundant regional block faulting and the beginning of an environment with a thermal subsidence-dominated regime [43,59].…”

“…Microbial carbonate production, phosphogenesis, and karst development were described a few kilometers to the west of Tizert in the Basal Series onlapping the Ouaoufenga and Igherm inliers [59] and in the Basal Series of the southwestern High Atlas [71]. C and O isotopic analysis of calcite speleothems of the karst cavities are characterized by lighter 18 O PDB and 13 C PDB composition (−6.9 < 18 O PDB < −8.1 and −8.2 < 13 C PDB < −8.5) than the host-rock dolomite (−4.2 < 18 O PDB < −8.1 and −3.7 < 13 C PDB < −0.2) indicating involvement of terrestrial fluids rich in decomposing organic matter and/or microbial activity [59].…”

The Jbel Saghro Au(–Ag, Cu) and Ag–Hg Metallogenetic Province: Product of a Long-Lived Ediacaran Tectono-Magmatic Evolution in the Moroccan Anti-Atlas

“…The first step occurs during the Cambrian, from the Terreneuvian to the Miaolingian. It corresponds to a rifting episode [84,86,97,98]. The Adoudou formation and related alkaline volcanic rocks mentioned above belong to this step.…”

Cambrian syn‐rift tectonic pulses at unconformity‐bounded carbonates in the Avalon Zone of Newfoundland, Canada

“…Pulses of rifting generated both accommodation space and networks of narrow, interconnected rifting branches bounded by disconnected shoulders that were locally tilted and uplifted. These led to sharp changes in lithology and facies thickness, episodic deposition of conglomerates and breccias along rift flanks, local tilting and uplift along rift shoulders associated with subaerial exposure, development of hydrothermally induced metal ore deposits and local stratigraphic gaps and deposition of deeper water facies along the axes of rift branches (Álvaro, 2013Álvaro & Clausen, 2007Álvaro & Clausen, , 2008Álvaro et al, 2015;Álvaro & Subías, 2011).…”