Paul F. Hoffman

Paul F. Hoffman
University of Victoria | UVIC · School of Earth and Ocean Sciences

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110
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Publications

Publications (110)
Article
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The Trezona carbon isotope excursion is recorded on five different continents in platform carbonates deposited prior to the end-Cryogenian Marinoan glaciation (>635 Ma) and represents a change in carbon isotope values of 16-18‰. Based on the spatial and temporal reproducibility, the excursion previously has been interpreted as tracking the carbon i...
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Otavi Group is a 1.5−3.5-km-thick epicontinental marine carbonate succession of Neoproterozoic age, exposed in an 800-km-long Ediacaran−Cambrian fold belt that rims the SW cape of Congo craton in northern Namibia. Along its southern margin, a contiguous distally tapered foreslope carbonate wedge of the same age is called Swakop Group. Swakop Group...
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Estimated at ~58 Myr in duration, the Sturtian snowball Earth (ca. 717‐659 Ma) is one of the longest‐known glaciations in Earth history. Surprisingly few uncontroversial lines of evidence for glacial incisions associated with such a protracted event exist. We report here multiple lines of geologic field evidence for deep but variable glacial erosio...
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The oxygenation of Earth’s surface environment dramatically altered key biological and geochemical cycles and ultimately ushered in the rise of an ecologically diverse biosphere. However, atmospheric oxygen partial pressures (pO2) estimates for large swaths of the Precambrian remain intensely debated. Here we evaluate and explore the use of carbona...
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A central prediction of the Snowball Earth hypothesis is that glacial onset should be synchronous at low latitudes, and its termination should be rapid and synchronous globally. Synchronous onset of the Sturtian (ca. 716 to ca. 660 Ma) has been robustly shown on multiple continents through the application of high precision U-Pb zircon dating. Succe...
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A geometrically quantitative plate-kinematic model, based on paleomagnetism, for the initial assembly of Laurentia has taken form in the past few decades. Within this framework, there remains but one problematic interval of data predominantly from the Slave craton, which is the 1.96–1.87Ga Coronation apparent polar wander path (APWP). The Coronatio...
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Geological evidence indicates that grounded ice sheets reached sea level at all latitudes during two long-lived Cryogenian (58 and ≥5 My) glaciations. Combined uranium-lead and rhenium-osmium dating suggests that the older (Sturtian) glacial onset and both terminations were globally synchronous. Geochemical data imply that CO 2 was 10 2 PAL (presen...
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Cryogenian synglacial deposits are regionally thin but locally thick, considering glacial duration, but the reasons for local thickening are poorly known. We studied three local thickenings of the Sturtian Chuos Formation in northern Namibia by measuring closely spaced columnar sections, not only of the synglacial deposits but also of the bounding...
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Historians often remark on scientists’ selective memories concerning their work. Nevertheless, scientists leave excellent contemporary records. Most scientists publish frequently throughout their careers, and it is safe to assume that what they submit for peer review represents their best scientific judgment at that time.
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Tuzo Wilson’s well-known pre-1961 opposition to continental drift stemmed from his early experience as a geologist in the Appalachians and the Canadian Shield, which convinced him that orogenesis did not change drastically over geologic time. Conversely, Taylor (in 1910) and Wegener (in 1912) hypothesized that continental drift began in Cenozoic or...
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Neoproterozoic successions in NE Svalbard and East Greenland host a pair of glacigenic formations, the younger of which are correlated with the terminal Cryogenian (Marinoan) glaciation based on their lithologically and isotopically diagnostic cap dolostones. A deep negative carbon isotope excursion (CIE) occurs stratigraphically beneath the older...
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Interpretations of major climatic and biological events in Earth history are, in large part, derived from the stable carbon isotope records of carbonate rocks and sedimentary organic matter. Neoproterozoic carbonate records contain unusual and large negative isotopic anomalies within long periods (10-100 million years) characterized by δ(13)C in ca...
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Tanja Bosak, Nicolas Dauphas, Arlene M. Fiore, Adam C. Maloof, and Christian Schoof were awarded the 2011 James B. Macelwane Medal at the AGU Fall Meeting Honors Ceremony, held on 7 December 2011 in San Francisco, Calif. The medal is for “significant contributions to the geophysical sciences by an outstanding young scientist.”
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Orthochemical sediments associated with Neoproterozoic glaciation have prominence beyond their volumetric proportions because of the insights they provide on the nature of glaciation and the records they hold of the environment in which they were precipitated. Synglacial Fe formations are mineralogically simple (haematite jaspilite), and their trac...
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Neoproterozoic glacial records have been discovered on 23 palaeocontinents, their rate of discovery changing little since 1871. Yet, half of all the resulting publications appeared since 2000. The history of research before 1998 is described in five stages defined by publication spikes; subsequent work is not covered because historical perspective...
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We have measured the iron isotope compositions and trace element concentrations of a suite of iron formation (IF) samples from the Neoproterozoic Rapitan Group, which was deposited during the older of two glacial episodes recorded in the Windermere Supergroup of the northern Canadian Cordillera. Like most other Neoproterozoic examples, iron in the...
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Our detailed examination of the Ghaub Formation (possibly 635 Ma) on the distal foreslope of the Otavi carbonate platform is part of a regional study of the Congo paleocontinental margin in northwestern Namibia. Detrital carbonates of the Ghaub Formation disconformably overlie the Franni-aus Member of the Ombaatjie Formation, a coarsening-upward st...
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Athapuscow aulacogen is an Early Proterozoic intracratonic basin located in the East Arm of Great Slave Lake between the Slave and northwest Churchill provinces. Athapuscow aulacogen comprises three stratigraphic sequences, the Wilson Island Group, the Great Slave Supergroup, and the Et-Then Group. New U–Pb zircon ages provide constraints on the de...
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The Cape Smith Belt is one of the most interesting and controversial of the proposed geosutures in the Canadian Shield. A new tectonic model is presented in which the mafic–ultramafic thrust sheets of the belt constitute a klippe, 20 000 km2 in area, separated from underlying basement of Superior Province and its thin autochthonous cover by a conti...
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Nearly 40 000 ft (~12 190 m) of unmetamorphosed Aphebian (and possibly lowermost Helikian) sedimentary and volcanic rocks are exposed in the East Arm of Great Slave Lake. This sequence is an erosional remnant of an Appalachian-type geosynclinal complex with a NNW depositional strike. Integrated paleocurrent, stratigraphic, and sedimentological anal...
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The 1.9 Ga Coronation "geosyncline'' to the west of Slave craton was among the first Precambrian continental margins to be identified, but its duration as a passive margin has long been uncertain. We report a new U-Pb (isotope dilution - thermal ionization mass spectrometry (ID-TIMS)) (207)Pb/(206)Pb date of 2014.32 +/- 0.89 Ma for zircons from a f...
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Paul F. Hoffman was awarded the 2010 Walter H. Bucher Medal at the AGU Fall Meeting Honors Ceremony, held on 15 December 2010 in San Francisco, Calif. The medal is for ``original contributions to the basic knowledge of the crust and lithosphere.''
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Tectonic fold tests conducted in Namibia demonstrate that the inclination with respect to bedding of geoplumb (palaeovertical) tubular structures in the Marinoan (635 Ma) syndeglacial cap dolostone is mainly the result of tectonic strain. Therefore, tubestone inclination data cannot be used to estimate the gradient of the sea floor on the foreslope...
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There is now irrefutable geological evidence that tropical ice sheets flowed directly into Earth's oceans at 716 Ma (Sturtian glaciation) and again at 635 Ma (Marinoan glaciation). Yet, the sparse fossil record suggests that the ocean was never entirely shuttered by a limitless ice shelf (`sea glacier'). This dilemma has encouraged numerical simula...
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Sheet-crack cements and coextensive intrastratal folds and breccias occur in a stratigraphically controlled, meter-thick zone, near the base of Marinoan (635 Ma) cap dolostones in slope settings. We demonstrate that sheet-crack cements on the margins of the Congo and Kalahari cratons are localized at a turbidite-to-grainstone transition, which reco...
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The shapes of plutons and their emplacement mechanisms, the connection between the volcanic and plutonic realms, and the development of batholiths have been of interest to geologists since they realized that plutons were once low viscosity magma. These issues have proven difficult to resolve because there are few places that have enough relief to e...
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Microbial structures in Neoproterozoic cap carbonates record the environmental processes present in the aftermath of global glaciation. The Rasthof Formation of northern Namibia is a unique carbonate depositional sequence that formed during post-glacial transgression and highstand following the Chuos glaciation. Carbon isotope profiles from four ex...
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The Coronation loop is a 110° arcuate sweep of 15 paleomagnetic poles with ages of ca. 1950–1850 Ma, derived from contemporaneous basins on the western (Coronation), southern (Great Slave) and eastern (Kilohigok) margins of the Slave craton in the northwestern Canadian shield. Although the paleomagnetic results are either demonstrated as primary or...
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The Wopmay orogen is a Paleoproterozoic orogenic belt formed in part by the accretion of Hottah terrane, an east-facing continental magmatic arc, to the western margin of the Archean Slave craton at ca. 1.88 Ga. The arc-continent collision was responsible for the Calderian orogeny. Just prior to the collision, arc volcanism of the Hottah terrane ha...
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The Cottons Breccia of King Island, Tasmania, is a 100-m-thick carbonate-clast diamictite traditionally interpreted as the product of a Cryogenian or Ediacaran glaciation. It was recently reinterpreted as a mass-flow deposit, unrelated to glaciation, within an active rift basin. We reaffirm the glacial–periglacial interpretation on the basis of sed...
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The distributions of 77 Neoproterozoic glacigenic formations are shown on global palaeogeographic maps for 715 Ma (Sturtian), 635 Ma (Marinoan) and 580 Ma (Ediacaran), constructed on grounds independent of palaeoclimatic indicators. The meridional distribution of Sturtian and Marinoan deposits is biased in favour of low palaeolatitudes, whereas Edi...
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Radiative energy-balance models reveal that Earth could exist in any one of three discrete climate states—‘non-glacial’ (no continental ice-sheets), ‘glacial-interglacial’ (high-latitude ice-sheets) or ‘pan-glacial’ (ice-sheets at all latitudes)—yet only the first two were represented in Phanerozoic time. There is mounting evidence that pan-glacial...
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The 'snowball Earth' hypothesis interprets geological evidence as indicating multi-million-year episodes of global glaciation near the beginning and end of the Proterozoic eon. On the basis of a coupled carbon cycle-climate model, Peltier et al. propose that temperature-dependent remineralization of organic carbon in a Neoproterozoic ocean with 100...
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The pan-glacial episode ending in 635 Ma occurred while the Otavi Group in northern Namibia was a flat- topped carbonate platform with a well-defined, south-facing, submarine foreslope undergoing thermal subsidence. Glacial erosion produced 5 km seaward of the platform edge, bears a laterally-continuous prism of structureless diamictites and well-s...
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In the Otavi Group of Namibia, 900 m of platform carbonate strata above the 635-Ma post-glacial cap dolostone are consistently lighter in delta13C by up to 2.5 per mil than the adjacent 180-320 m of correlative, >0.6-km-deep, foreslope strat. Assuming the foreslope carbonate was equilibrated with deeper water, the normal isotopic gradient dynamical...
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In Climate Through the Ages (1926), C.E.P. Brooks distinguished two discrete climate states in the Phanerozoic, non-glacial (no continental ice sheets) and glacial-interglacial (1-4 continental ice sheets). It now appears that pan-glacial climate states (ice sheets on all continents) existed near the beginning and end of the Proterozoic eon, around...
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Fe speciation and S-isotope of pyrite data from the terminal Proterozoic Sheepbed Formation in Canada and Doushantuo Formation in China reveal that ocean deep waters were anoxic after the global glaciations (snowball Earth) ending 635 million years ago, but that marine sulfate concentrations and inferentially atmospheric oxygen levels were higher t...
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A layer of shallow-water dolostone (“cap dolostone”) with idiosyncratic sedimentary structures was deposited across continental margins world-wide in the aftermath of the terminal Cryogenian snowball Earth. The dolostone has a global average thickness of 18.5 m and is interpreted stratigraphically in different ways in the current literature: as dia...
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In his report of the Snowball Earth 2006 conference in Ascona, Switzerland, coconvenor Philip A. Allen described the ‘original pillars’ of the hypothesis as having “been discarded” [Allen, 2006]. From my reading of the hypothesis [Kirschvink, 1992a, 1992b; J.L. Kirschvink, personal communication, 1989], the original pillars are the following. Each...
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We present new paleomagnetic data from three Middle Neoproterozoic carbonate units of East Svalbard, Norway. The paleomagnetic record is gleaned from 50 to 650 m of continuous, platformal carbonate sediment, is reproduced at three locations distributed over >100 km on a single craton, and scores a 5-6 (out of 7) on the Van der Voo (1990) reliabilit...
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We have analyzed δ34S (sulfate and pyrite), δ18Ocarbonate and δ13Ccarbonate, and major and trace elemental concentrations, including extractable Fe and Mn phases, in four sections of the Maieberg Formation, the cap-carbonate sequence to the Marinoan glaciation in northern Namibia. δ34Ssulfate profiles and other geochemical characteristics in the ba...
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In Neoproterozoic time, East Greenland and East Svalbard (EGES) occupied landward and seaward positions, respectively, on the southern subtropical margin of Laurentia. In both areas, thick clastic-to-carbonate successions are overlain by two discrete glacial and/or periglacial formations, separated by fine basinal clastics. In Svalbard, the younger...
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The snowball earth hypothesis is a unified theory accounting for the global distribution of Cryogenian (roughly 720 to 635 Ma) glacial and glacial marine deposits, their global synchroneity demonstrated by chemostratigraphy, and their close association with thick carbonate strata and sedimentary iron deposits (banded iron formation) in certain area...
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Glacial deposits of Sturtian and Marinoan age occur in the well-studied Neoproterozoic successions of northern Namibia, South Australia, and northwestern Canada. In all three regions, the Marinoan glaciation is presaged by a large negative δ13C anomaly, and the cap carbonates to both glacial units share a suite of unique sedimentological, stratigra...
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Jerolmack and Mohrig suggest that the wave- ripple structure we describe from cap carbonates deposited in the aftermath of the Marinoan glaciation was created under storms or hurricanes similar to those experienced today on certain oceanic coasts, citing a documentation of large wave ripples on the seabed off the coast of North Carolina. Side-scan...
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Urey’s carbonate oxygen isotope paleothermometer is a milestone of paleoclimate research but constrains temperature only if the oxygen isotope composition of water from which carbonate grew is known. Moreover, difficulty in recognizing diagenetic overprinting has confounded the interpretation of carbonate oxygen isotope compositions for much of the...
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The most severe excursions in the Earth's climatic history are thought to be associated with Proterozoic glaciations. According to the 'Snowball Earth' hypothesis, the Marinoan glaciation, which ended about 635 million years ago, involved global or nearly global ice cover. At the termination of this glacial period, rapid melting of continental ice...
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Two separate and distinct diamictite-rich units occur in the mixed carbonate-siliciclastic Polarisbreen Group, which comprises the top kilometer of >7 km of Neoproterozoic strata in the northeast of the Svalbard archipelago. The platformal succession accumulated on the windward, tropical to subtropical margin of Laurentia. The older Petrovbreen Mem...
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We sketch a conceptual model of the glacial history of a snowball Earth, based on new field studies of Marinoan (c640 Ma), Sturtian (c710 Ma) and Huronian (c2.4 Ga) syn-glacial deposits, and informed by sea-ice dynamics modeling. If the oceans froze over from pole to pole, sea ice would thicken and flow glacially towards the Equator, maintained in...
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Recent model experiments suggest that marine ice dynamics are important in the initiation and development of a snowball Earth. Ice-line advance is facilitated by the transport of latent heat and freshwater associated with Ekman forcing in the zone of westerlies (Lewis et al., 2002 this meeting) and with equatorward glacial flow of thick, multi-annu...
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The geological and geochronological data on the timing of Early Proterozoic orogenic belts in Laurentia (the North American craton) are discussed. Collisions in the northern and accretion in the southern part of the craton are examined in detail. The geological composition of the various parts of each region are described, and the ways that they ca...
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We propose that there were three Neoproterozoic glaciations. The critical event is the second, Marinoan, glaciation, the most widespread and most easily recognised. Marinoan glacial deposits are overlain by a distinctive transgressive, laminated cap-dolostone, which variably contains isopachous cements, accretionary oscillation megaripples, tubesto...
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Detailed lithostratigraphic studies on the transition from non diamictite to diamictite intervals within the Neoproterozoic are vital in evaluating the nature of presumed glacial events in the Snowball Earth hypothesis. To this goal we examined the fine-scale stratigraphic relationships of units above and below the Ghaub carbonate diamictite in the...
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The gradual discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum. Was the Earth's orbital obliquity > 60° (making the tropics colder than the poles) for 4.0 billion years following the lunar-forming impact, or did climate cool globally for some reason to the point at which runawa...
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1] A large (11–15%) negative shift in d 13 C is observed in shallow water carbonates directly beneath Neoproterozoic glacial deposits (or correlative disconformity) in northwest Namibia ascribed to a snowball Earth. Reproducibility and stratigraphic concordance of this anomaly in 16 sections across the ancient continental shelf support a primary or...
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1] The Snowball Earth hypothesis explains the development of glaciation at low latitudes in the Neoproterozoic, as well as the associated iron formations and cap carbonates, in terms of a runaway ice-albedo feedback leading to a global glaciation followed by an extreme greenhouse climate. The initiation of a snowball glaciation is linked to a varie...
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[Kennedy et al. (2001)][1] propose a creative scenario to explain the unique occurrence of 13C-depleted “cap” carbonates on top of Neoproterozoic glacial deposits. It is roughly as follows: Organic-rich marine sediments are subaerially exposed by sea-level fall during glaciation. Methane
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According to the 'snowball Earth' hypothesis, a series of global glaciations occurred 750-580 million years ago, each lasting for millions of years and ending in a scorching heat caused by an extreme enrichment of atmospheric greenhouse gases. Hyde et al. have used climate models to simulate this global glaciation, finding in one case an alternativ...
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Ten arguments were recently presented in The Australian Geologist (1) against the 'snowball Earth' scenario for equatorial glaciation, a scenario that explains many previously enigmatic features of Neoproterozoic Earth history such as post-glacial cap carbonates, large shifts in stable isotope ratios of seawater proxies, and extensive oxide-facies...
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Iceentombed our planet hundreds of millions ofyearsago, and complex animals evolved in the greenhouse heat wave that followed
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A major global plate reorganisation occurred between ∼750 and ∼550 Ma. Gondwana was assembled following the dispersal of Rodinia, a supercontinent centred on Laurentia in existence since ∼1050 Ma. The reorganisation began when tectonic elements, later composing East Gondwana, rotated piecemeal away from the Pacific margin of Laurentia. These elemen...
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The Ombonde detachment is a primary low-angle normal fault that developed in an undeformed Neoproterozoic carbonate shelf succession as it entered a west-dipping Pan-African subduction zone. The fault is mappable from the top of the shelf succession to the granitic basement surface at a paleodepth of 1.5 km, and the hanging wall has not been signif...