Harmon D. Maher

Manifestations of the Cretaceous High Arctic Large Igneous Province in Svalbard

Abstract Major Cretaceous Large Igneous Provinces (LIPs, e.g., Kerguelen and Ontong Java) show Aptian magmatic peaks and are linked to global mantle overturning and anomalous surface conditions. Widespread Cretaceous igneous activity in the High Arctic has recently been identified as a LIP. Exposed components on Svalbard, Franz Josef Island, adjacent shelf areas, Axel Heiberg and Ellesmere Islands, and perhaps North Greenland, cover several hundred thousand square kilometers and were peripheral to a LIP center at the Alpha Ridge. Manifestations of LIP development on Svalbard include (1) extensive sills, rare dikes, and extrusives in the east, (2) slow regression within the upper part of thick, black shales punctuated by locally abrupt uplift, with overlying coastal plain sandstones, (3) development of a regional, Late Cretaceous, low‐angle unconformity associated with a second regression, and (4) a widespread Early Aptian transition from quartz arenites to lithic arenites and feldspathic sandstones reflec...Major Cretaceous Large Igneous Provinces (LIPs, e.g., Kerguelen and Ontong Java) show Aptian magmatic peaks and are linked to global mantle overturning and anomalous surface conditions. Widespread Cretaceous igneous activity in the High Arctic has recently been identified as a LIP. Exposed components on Svalbard, Franz Josef Island, adjacent shelf areas, Axel Heiberg and Ellesmere Islands, and perhaps North Greenland, cover several hundred thousand square kilometers and were peripheral to a LIP center at the Alpha Ridge. Manifestations of LIP development on Svalbard include (1) extensive sills, rare dikes, and extrusives in the east, (2) slow regression within the upper part of thick, black shales punctuated by locally abrupt uplift, with overlying coastal plain sandstones, (3) development of a regional, Late Cretaceous, low‐angle unconformity associated with a second regression, and (4) a widespread Early Aptian transition from quartz arenites to lithic arenites and feldspathic sandstones reflecting new northern volcanic source terranes. The unconformity likely reflects LIP thermal doming with >1 km of erosion. The sedimentologic record provides important insight into this LIP since much of it is inaccessible or eroded. Analysis of published geochronology indicates magmatism within a 135–90 Ma window, with more detailed interpretations being problematic. Two regressions suggest two pulses of igneous activity (Barremian and Albian). Multiple pulses have been documented for other LIPs and may result from a deep and large plume. Present evidence that magmatism was coeval in Svalbard and Franz Josef Land is inconsistent with a hotspot track hypothesis and suggestive of a large initial plume head.

Application of a critical wedge taper model to the tertiary transpressional fold-thrust belt on Spitsbergen, Svalbard

The Tertiary opening of the North Atlantic Ocean involved major and long-lived overall dextral transpression between the Svalbard and Greenland plates. On Spitsbergen, this tectonic event is manifest as a 100–200-km-wide contractional fold-thrust belt in the form of an east-pinching prism. This belt can be subdivided into (1) a western, basement-involved hinterland province that reveals more complex deformation, including thrust, transcurrent, and normal faulting, and (2) an eastern thin-skinned fold-thrust belt with structures oriented subparallel (north-northwest–south-southeast) to the transform plate boundary. The time-space distribution and interaction of different structural styles of Tertiary deformation evident on Spitsbergen support a model with linked, long-term and short-term (episodic) dynamic growth of a composite contractional and transcurrent fold-thrust wedge. The growth of a narrow, high-taper (critical-supercritical) contractional wedge occurred during northward-directed crustal shortening (stage 1) in an oblique, dextral transcurrent setting. Crustal thickening in the form of thrust uplift and basin inversion and strike-slip duplexing during the main contractional event (stages 2 and 3) created an unstable, supercritical wedge of basement and cover rocks in the hinterland. At the same time, a broader and more homogeneous frontal part of the wedge developed eastward by in-sequence imbrication in order to reduce the taper angle. Local erosion and lateral wedge extrusion (stages 3 and 4) modified the oversteepened hinterland wedge to a critical taper angle. Continued tectonic activity in the hinterland caused renewed internal imbrication of the frontal wedge, where deformation was accommodated by tear faulting and out-of-sequence thrusting (stage 4). Adjustment toward a stable taper geometry included local extension (stage 5) and erosion and sedimentation. In a transpressional fold-thrust belt, as on Spitsbergen, out-of-plane (orogen oblique to parallel) transport in the hinterland may cause local and lateral supercritical and subcritical wedge tapers. Hinterland geometries could trigger adjustments in a frontal thrust wedge in a decoupled situation, and/or orogen oblique or parallel motions in a coupled situation. Changing kinematics may thus be expected along strike in such an orogen.

Structural outline of a Tertiary Basement-cored uplift/inversion structure in western Spitsbergen, Svalbard: Kinematics and controlling factors

The Tertiary fold-and-thrust belt of Spitsbergen can be divided into a western basement-involved fold-thrust stack and a central-eastern foreland fold-and-thrust belt. In western Nordenskiold Land the first-order structure is an ENE-verging basement-cored fold and fault complex involving Paleozoic to Tertiary strata. The northern part reveals an upright, monocline geometry of east tilted sedimentary cover units with associated layer parallel to low-angle thrusts and folds. These structures consist of two populations oriented both parallel to (NNW–SSE) and oblique to (WNW–ESE) the general structural trend of the fold complex. In the central and southern parts of west Nordenskiold Land the fold complex involves tilted basement cut by steep, transverse faults and late normal faults. The east limb of the fold complex displays repeated basement and Paleozoic strata (Orustdalen formation) in its core and Mesozoic (Triassic) strata influenced by map-scale chevron folds and two decollement levels, all located above an eastward rotated, major detachment fault, the Kleivdalen Thrust. Establishing fold-fault relations includes a three-stage structural history in the fold complex as follows: (1) a phase of early NNE–SSW shortening associated with WNW–ESE folds and thrusts and (2) a dominant ENE–WSW, basement-involved shortening leading to the first-order, NNW–SSE-striking fold complex, followed by (3) approximately E–W extension. The resulting structures and structural variability along strike as well as across strike appear to have been controlled by basement and Carboniferous basin structures underlying the Permian-Cretaceous platform strata. Restored stratigraphic sections based on thrust-repetition of basement and cover (e.g., within a type section of the Carboniferous Orustdalen formation) support such an interpretation. A tentative inversion tectonic model reproduces the position(s) of local and major thrust ramps and associated folds, as a result of inheritance from Carboniferous basin structures.

Svartfjella, Eidembukta, and Daudmannsodden lineament: Tertiary orogen-parallel motion in the crystalline hinterland of Spitsbergen's fold-thrust belt

Within metamorphic basement rocks of the hinterland of Spitsbergens Tertiary fold-thrust belt, a 35-km-long zone of notably deformed Carboniferous strata and Cretaceous intrusives forms a major orogen-parallel lineament from Svartfjella to Eidembukta to Daudmannsodden (SEDL). Orientations and geometries of map-scale fault duplexes and associated fault plane-striae populations, of folds and associated cleavage, and of tension gashes all indicate orogen-parallel motion occurred along the SEDL. Structural analyses indicates three phases: 1) ENE-directed overthrusting, 2) sinistral motion with a backthrust component, and 3) dextral strike-slip motion. This history indicates a change from orogen-perpendicular to orogen-parallel movements. Orogen-parallel movement was likely coeval with orogen-perpendicular fold-thrust transport to the ENE in the foreland. A model where dextral transpressive motion between Greenland and Svalbard was decoupled explains the hinterland-foreland difference. Basement fabric aligned with Carboniferous carbonates on the steep foreland face of an antiformal stack provided a through-going weak surface, a prerequisite for decoupling. Sinistral orogen parallel motion is explicable by short-lived episode of sinistral plate motion or by local wedge extrusion during dextral transpression. The evolution of decoupling patterns has significant implications for deducing plate motions from local kinematic and paleostress studies.

Kinematics of Tertiary structures in upper Paleozoic and Mesozoic strata on Midterhuken, west Spitsbergen

A belt of folded and faulted Carboniferous-Cretaceous platform cover strata lies parallel to and inland of much of Spitsbergen9s west coast. Uplifted older basement rocks along the coast have been thrust eastward into and over these younger platform cover strata. This deformation occurred in early Tertiary time and was related to dextral movement of the Barents Shelf past northeastern Greenland during the opening of the Norwegian-Greenland Sea. On Midterhuken, a peninsula in Bellsund, an uplifted, tilted, and faulted sequence of the cover strata forms a 3.3-km-thick, 12-km-wide margin on the eastern side of the basement crustal welt. A series of closely spaced detachment horizons within Triassic strata occurs at the boundary between a lower unit of mainly sandstones and an upper unit of mainly thin-bedded shales and siltstones. The lower unit is tilted 60°–70° to the northeast but unfolded, whereas the upper unit is tightly and disharmonically folded. Hanging-wall–down movements on these and other detachment surfaces are indicated by offset of a dike and by fold-and-fault patterns. These foreland-dipping faults might be southwest-dipping thrusts later rotated, but more likely these faults and associated folds represent detachment structures formed close to their present position in response to the uplift and tilting of these strata.

Tertiary or Cretaceous age for Spitsbergen's fold‐thrust belt on the Barents Shelf

Several publications propose that main-phase fold-thrust development on Spitsbergen was Late Cretaceous and not Tertiary as previously thought. The question of timing is crucial to models for crustal response to transpressive plate motions. Involvement of Tertiary strata in fold-thrust structures, the sedimentology of the Tertiary basin strata, and studies of paleo-stress field evolution all indicate Paleocene to Eocene fold-thrust development during opening of the Norwegian-Greenland oceanic basin. A regional angular unconformity of < 1° between Paleocene and Early Cretaceous strata is consistently disconformable to the eye and precludes any significant older deformation in the immediate area. Pre-unconformity deformation was likely strike slip in character and concentrated in the west. The proposal for Late Cretaceous fold-thrust belt formation is inconsistent with the geology.

Tectonic evolution of the west Spitsbergen fold belt

Abstract The west Spitsbergen fold belt has a complex tectonic history which is recorded in a thick, nearly complete upper Proterozoic-Phanerozoic layered sequence. Work since 1977 near Bellsund allows recognition of the main deformational events in that segment of the fold belt. The strata are grouped informally into the metamorphosed Hecla Hoek (HH) sequence (Proterozoic) and the Van Keulenfjorden (VK) sequence (Carboniferous-Cretaceous), separated by a pronounced unconformity. The HH is divided into the Antoniabreen succession, the Chamberlindalen succession, and the Kapp Lyell tillite; the first two consist of diverse clastic and carbonate rocks, along with some volcanic rocks. The VK is a platform sequence of shallow marine and terrestrial sedimentary rocks. These layered rocks are intruded by a few Mesozoic dolerite sills and dikes. Subhorizontal Paleogene sedimentary rocks are preserved in a small graben. Both layered sequences have undergone strong deformation. Structures (mainly Caledonian age) in the HH can be grouped as phase 1 (small isoclinal folds, subhorizontal axial planar foliation, ridge-groove lineation in the foliation, and large recumbent folds), phase 2 (tight to isoclinal folds, axial planar foliation), and younger (weak folds and foliations, kink bands, crinkles). Structures (mainly Tertiary age) in the VK include faults (thrust, reverse, down-to-the-east bedding-plane normal, other normal); folds (symmetric, asymmetric, overturned, recumbent, isoclinal); and foliation (in some tightly folded Triassic shales). Six deformational events can be identified here, each described below in terms of age, intensity, and kinematic pattern: • D1 - Vendian or early Paleozoic; very strong; NNW-SSE shortening?, NNW transport? • D2 - Early Paleozoic (pre-Carboniferous); strong; NE-SW shortening, NE vergence. • D3 - Middle (?) Carboniferous; moderate; unclear (limited exposure). • D4 - Early Cretaceous (?); weak; extension, direction unclear. • D5 - Early (?) Tertiary; very strong locally; uplift in W, ENE-WSW shortening, ENE translation. • D6 - Middle (?) Tertiary; moderate; NE-SW extension.

Late Devonian transpressional tectonics in Spitsbergen, Svalbard, and implications for basement uplift of the Sørkapp-Hornsund High

Abstract: The Late Devonian Svalbardian event relates to the final activity in the Caledonian Orogen, and affected Devonian strata in Spitsbergen by major folding, oblique thrusting and basement uplift. In southern Spitsbergen, the Devonian deformation and the complementary, presumed Mid-Carboniferous Adriabukta event deformation caused uplift of the Sørkapp–Hornsund basement high or horst. This high is fault-bounded by Devonian sandstones and a questionably aged Early or Mid-Carboniferous mudstone unit (Adriabukta Formation). The Adriabukta Formation at Hornsund occurs in the core of a major syncline, with underlying Devonian strata in the west limb, all truncated in the footwall by a steep, east-side-up oblique-reverse fault. Mid- to Late Carboniferous rifting reversed the motion and produced rift-fill deposits, and these strata overlie the deformed Devonian rocks and the Adriabukta Formation with an angular unconformity. A similar basin architecture and major syncline bounded by a reverse fault with lateral movement characterize the Svalbardian deformation in the Mimerdalen–Pyramiden area at Billefjorden farther north. Similarity also exists between a Late Devonian unit (Plantekløfta Formation) at Mimerdalen and the Adriabukta Formation at Hornsund, and we question the previous interpretation of the Adriabukta Formation as Carboniferous. Rather, we suggest that the Adriabukta and Svalbardian deformation events may have been part of the same event.

Tertiary divergent thrust directions from partitioned transpression, Brøggerhalvøya, Spitsbergen

Broggerhalvoya, located at the northwestern terminus of Spitsbergens Tertiary fold-thrust belt, is underlain by a basement-involved thrust stack defined by an anomalous WNW-ESE strike direction relative to the overall NNW-SSE strike further south. Three kinematically separable thrust nappes are identified: (i) a lower nappe is characterized by low-angle to bedding-parallel imbricates, (ii) a middle nappe comprises macroscopic anticlines and synclines, rotated imbricate fans and duplexes within Palaeozoic-Mesozoic cover strata, and (iii) an upper nappe consists of overthrust Caledonian basement rocks. In addition, steep N-S-striking oblique-normal faults offset the fold-thrust stack and can be traced southwards into parallelism with the Forlandsundet Graben and a major transcurrent fault, the Svartfjella-Eidembukta-Daudmannsodden Lineament. A three-phase kinematic development of the nappes and bounding thrust systems is invoked: (i) an early phase of basement-involved uplift and foreland thrusting of the ...

Caledonian thrusting on Bj rn ya: Implications for Palaeozoic and Mesozoic tectonism of the western Barents Shelf

The late Proterozoic to Ordovician rocks on Bjornoya, located on the western Barents Shelf, experienced significant contractional deformation during the Caledonian orogeny, contrary to some descriptions. Major thrust zones bound the various pre-Devonian basement units of the island, and the Upper Riphean-Vendian to Middle Ordovician rocks are stacked in a WNW-verging thrust pile. In detail, mesoscopic structures, such as ductile shear folds and fabrics, brittle faults with appropriate slip-lines, and stacked units, support a contractional nature of the deformation. An unconformity with overlying Upper Devonian sandstones truncates all the major basement thrusts, thereby indicating a Caledonian age for the major deformation of the basement units. Later, Palaeozoic normal faults dissect the basement units and upper Devonian to mid-Carboniferous cover rocks. During this faulting episode, all units were also folded into a monocline. A strong similarity in orientation of the basement- and cover-related fault p...