Tectonic Reconstructions Research Articles

Gondwana breakup: no evidence for a Davie Fracture Zone offshore northern Mozambique, Tanzania and Kenya

AbstractPlate tectonic reconstructions assume a major inactive transform fault, the Davie Fracture Zone, in the West Somali Basin, along which Madagascar is thought to have migrated southwards following Gondwana breakup in the Mesozoic. Based on the interpretation of reflection seismic data, we show that the Walu Ridge offshore Kenya and the Kerimbas Basin offshore northern Mozambique are tectonically unrelated to the southward motion of Madagascar and correlate with Late Cretaceous volcanism and inversion in Kenya and the evolution of the East African Rift System respectively. Offshore Tanzania, geophysical data do not show basement structures indicating the presence of a major transform fault. These results challenge the commonly supported transform margin concept and imply a more southerly pre‐breakup position of Madagascar within Gondwana. Opening of the West Somali Basin by SW‐propagating oblique rifting and seafloor spreading is proposed.

The Mount Hay block, central Australia: Another puzzle piece for Paleo-Mesoproterozoic tectonic history

The 100km2 Mount Hay block (Arunta Region, central Australia) is a >15km thick crustal cross-section comprised of granulite facies tectonites containing a tectonothermal record from ca. 1803 to ca. 1552Ma, as demonstrated by the combination of prior work and new monazite geochronology and thermobarometry. Igneous and sedimentary protoliths formed ca. 1803–1798Ma during 1810–1790Ma Stafford–Tanami time. Between ca. 1790 and 1740Ma, nearly continuous magmatism in the Aileron Province, and possibly ages of recrystallized zircon and monazite in the Mount Hay block, record subduction along the southern margin of the Proterozoic Australia-Mawson continent. Geologic mapping and zircon and monazite geochronology demonstrate that the Mount Hay block was penetratively deformed between ca. 1720Ma and 1700Ma during 1735–1690Ma Strangways time. This includes the >8km thick Mount Hay sheath fold, which records NE-SW subhorizontal shear, once Paleozoic tilting of the Mount Hay block is removed. While still in the deeper crust (>798±33°C; >7.6±0.7kbar), fabrics along the northern edge of the Mount Hay block were transposed by the cross-cutting >7km thick Capricorn ridge shear zone at ca. 1551.7±5.5Ma, during Chewings time. Once restored, the Capricorn ridge shear zone records NE-SW extension. A jump in strain rate while at high temperatures (∼725°C) initiated severe localization accommodated initially by pseudotachylite formation and cataclasis then mylonitization during Fe-rich fluid flux. Shearing may have continued to pressure–temperature conditions as low as <630±25°C and ∼3–5±1.2kbar indicating ∼7–14km uplift. Fluid flow in the Capricorn ridge shear zone corresponds well with growing evidence for regional Fe±K±Si metasomatism with similar timing. In published tectonic reconstructions, Chewings aged deformation, including the Capricorn Ridge shear zone, may be related to subduction to the south, or re-convergence between the Proterozoic Australia-Mawson continent and Laurentia. Robust links between the kinematics of deformation and geochronologic constraints, and the ability to restore major structures to their original orientations, makes the Mount Hay block a valuable additional puzzle piece for Proterozoic tectonic reconstructions for Australia, and possibly the supercontinent Nuna.

First North American fossil monkey and early Miocene tropical biotic interchange.

New World monkeys (platyrrhines) are a diverse part of modern tropical ecosystems in North and South America, yet their early evolutionary history in the tropics is largely unknown. Molecular divergence estimates suggest that primates arrived in tropical Central America, the southern-most extent of the North American landmass, with several dispersals from South America starting with the emergence of the Isthmus of Panama 3-4 million years ago (Ma). The complete absence of primate fossils from Central America has, however, limited our understanding of their history in the New World. Here we present the first description of a fossil monkey recovered from the North American landmass, the oldest known crown platyrrhine, from a precisely dated 20.9-Ma layer in the Las Cascadas Formation in the Panama Canal Basin, Panama. This discovery suggests that family-level diversification of extant New World monkeys occurred in the tropics, with new divergence estimates for Cebidae between 22 and 25 Ma, and provides the oldest fossil evidence for mammalian interchange between South and North America. The timing is consistent with recent tectonic reconstructions of a relatively narrow Central American Seaway in the early Miocene epoch, coincident with over-water dispersals inferred for many other groups of animals and plants. Discovery of an early Miocene primate in Panama provides evidence for a circum-Caribbean tropical distribution of New World monkeys by this time, with ocean barriers not wholly restricting their northward movements, requiring a complex set of ecological factors to explain their absence in well-sampled similarly aged localities at higher latitudes of North America.

Tectonic evolution of the North Patagonian Andes (41°–44° S) through recognition of syntectonic strata

The North Patagonian fold-thrust belt (41°–44° S) is characterized by a low topography, reduced crustal thickness and a broad lateral development determined by a broken foreland system in the retroarc zone. This particular structural system has not been fully addressed in terms of the age and mechanisms that built this orogenic segment. Here, new field and seismic evidence of syntectonic strata constrain the timing of the main deformational stages, evaluating the prevailing crustal regime for the different mountain domains through time. Growth strata and progressive unconformities, controlled by extensional or compressive structures, were recognized in volcanic and sedimentary rocks from the cordilleran to the extra-Andean domain. These data were used to construct a balanced cross section, whose deep structure was investigated through a thermomechanical model that characterizes the upper plate rheology. Our results indicate two main compressive stages, interrupted by an extensional relaxation period. The first contractional stage in the mid-Cretaceous inverted Jurassic–Lower Cretaceous half graben systems, reactivating the western Cañadón Asfalto rift border ~500km away from the trench, at a time of arc foreland expansion. For this stage, available thermochronological data reveal forearc cooling episodes, and global tectonic reconstructions indicate mid-ocean ridge collisions against the western edge of an upper plate with rapid trenchward displacement. Widespread synextensional volcanism is recognized throughout the Paleogene during plate reorganization; retroarc Paleocene-–Eocene flare up activity is interpreted as product of a slab rollback, and fore-to-retroarc Oligocene slab/asthenospheric derived products as an expression of enhanced extension. The second stage of mountain growth occurred in Miocene time associated with Nazca Plate subduction, reaching nearly the same amplitude than the first compressive stage. Extensional weakening of the upper plate predating the described contractional stages appears as a necessary condition for abnormal lateral propagation of deformation.

Transpressional deformation, strain partitioning and fold superimposition in the southern Chinese Altai, Central Asian Orogenic Belt

Transpressional deformation has played an important role in the late Paleozoic evolution of the western Central Asian Orogenic Belt (CAOB), and understanding the structural evolution of such transpressional zones is crucial for tectonic reconstructions. Here we focus on the transpressional Irtysh Shear Zone with an aim at understanding amalgamation processes between the Chinese Altai and the West/East Junggar. We mapped macroscopic fold structures in the southern Chinese Altai and analyzed their relationships with the development of the adjacent Irtysh Shear Zone. Structural observations from these macroscopic folds show evidence for four generations of folding and associated fabrics. The earlier fabric (S1), is locally recognized in low strain areas, and is commonly isoclinally folded by F2 folds that have an axial plane orientation parallel to the dominant fabric (S2). S2 is associated with a shallowly plunging stretching lineation (L2), and defines ∼NW-SE tight-close upright macroscopic folds (F3) with the doubly plunging geometry. F3 folds are superimposed by ∼NNW-SSE gentle F4 folds. The F3 and F4 folds are kinematically compatible with sinistral transpressional deformation along the Irtysh Shear Zone and may represent strain partitioning during deformation. The sub-parallelism of F3 fold axis with the Irtysh Shear Zone may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear-dominant deformation (F3) in fold zones. The strain partitioning may have become less efficient in the later stage of transpressional deformation, so that a fraction of transcurrent components was partitioned into F4 folds.

Estimation and propagation of uncertainties associated with paleomagnetic directions

AbstractPrincipal component analysis (PCA) is a well‐established technique in paleomagnetism and provides a means to estimate magnetic remanence directions from univectorial segments of stepwise demagnetization data. Derived directions constrain past geomagnetic field behavior and form the foundation of chronological and tectonic reconstructions. PCA of isolated remanence segments relies on estimates of the segment mean and covariance matrix, which can carry large uncertainties given the relatively small number of demagnetization data points used to characterize individual specimens. Traditional PCA does not, however, lend itself to quantification of these uncertainties, and inferences drawn from paleomagnetic reconstructions suffer from an inability to propagate uncertainties from individual specimens to higher levels, such as in calculations of paleomagnetic site mean directions and pole positions. In this study, we employ a probabilistic reformulation of PCA that represents the unknowns involved in the data fitting process as probability density functions. Such probability density functions represent our state of knowledge about the unknowns in the fitting process and provide a tractable framework with which to rigorously quantify uncertainties associated with remanence directions estimated from demagnetization data. These uncertainties can be propagated readily through each step of a paleomagnetic reconstruction to enable quantification of uncertainties for all stages of the data interpretation sequence, removing the need for arbitrary selection/rejection criteria at the specimen level. Rigorous uncertainty determination helps to protect against spurious inferences being drawn from uncertain data.

Source and age of upper Transvaal Supergroup, South Africa: Age-Hf isotope record of zircons in Magaliesberg quartzite and Dullstroom lava, and implications for Paleoproterozoic (2.5–2.0 Ga) continent reconstruction

The Magaliesberg Formation quartzite of the upper Transvaal Supergroup in north-central South Africa represents the biggest Paleoproterozoic arenite deposit on Earth, with a present-day lateral extent of more than 600km. It therefore has a great potential to provide detailed information about Archean to early Paleoproterozoic crust–mantle evolution in the hinterland of the Kaapvaal Craton and for global plate tectonic reconstruction. Detrital zircons in Magaliesberg Formation quartzites provide evidence for magmatic activities in the source region at 2080–2130Ma (11%), 2220Ma (35%), 2350–2450Ma (8%) and, following an age gap of ca. 200millionyear, at 2650–2780Ma (11%), 2820–2910Ma (25%), and at 3060–3100Ma (6%). Minor zircon formation took place during Bushveld Complex contact metamorphism at 2055Ma, and less than 3% underwent a post-Bushveld age reset. Detrital zircons in a sediment-rich Dullstroom lava yield similar ages between 2120±12Ma and 2865.2±1.7Ma, indicating that Magaliesberg and post-Magaliesberg/Dullstroom sediments were derived from the same sources, and deposited between 2080 and 2055Ma. Distinct age spectra among the investigated quartzites indicate that the sandstone detritus was derived from different sources and rapidly deposited without complete homogenization, in a regressive shore line, braid-delta environment.Combined Hf isotope-age data reveal two distinct groups of zircon. Zircons of group I have Archean ages (>2.65Ga), and define a crustal array that points to protracted crust reworking in the hinterland between 3.10 and 2.65Ga. Likely sources for these zircons are granitoids of the Pietersburg Block, which is located at the northern edge of the Transvaal basin. Zircons of group II have Paleoproterozoic ages between 2.45 and 2.08Ga. They are mostly subchondritic, and show highly variable εHft between +4 and −19. These large variations hint to their formation in a magmatic arc and/or collisional setting. As granitoids with ages between 2.65 and 2.06Ga are absent on the Kaapvaal Craton, detrital zircons of such ages must have been derived from sources outside of the present-day craton. One potential source could be the Ophthalmia orogenic belt, which became amalgamated to the joined Kaapvaal–Pilbara and perhaps Zimbabwe cratons (Zim)vaalbara at 2.22–2.14Ga, whereas coeval magmatic rocks in southern America (e.g., Minero Belt of the Sao Francisco Craton) or West Africa can be excluded, as they were mostly derived from depleted mantle sources in oceanic environments. Abundant occurrence of detrital zircons with ages of 2.5Ga in the lower Pretoria Group (Duitschland Formation), but their complete absence in the upper Pretoria Group (Magaliesberg Formation), hint that (Zim)vaalbara was attached to an early Paleoproterozoic orogenic belt, which disappeared completely between 2.3 and 2.08Ga, most likely by cratonic break up.

Tectonic and stratigraphic evolution of the Western Alboran Sea Basin in the last 25 Myrs

The Western Alboran Basin (WAB) formation has always been the subject of debate and considered either as a back-arc or a forearc basin. Stratigraphic analyses of high-resolution 2D seismic profiles mostly located offshore Morocco, enabled us to clarify the tectonic and stratigraphic history of the WAB. The thick pre-rift sequence located beneath the Miocene basin is interpreted as the topmost Malaguide/Ghomaride complex composing the Alboran domain. The structural position of this unit compared with the HP–LT exhumed Alpujarride/Sebtide metamorphic basement, leads us to link the Early Miocene subsidence of the basin with an extensional detachment. Above the Early Miocene, a thick Serravallian sequence marked by siliciclastic deposits is nearly devoid of extensional structures. Its overall landward to basinward onlap geometry indicates that the WAB has behaved as a sag basin during most of its evolution from the Serravallian to the late Tortonian. Tectonic reconstructions in map view and in cross section further suggest that the basin has always represented a strongly subsiding topographic low without internal deformation that migrated westward together with the retreating slab. We propose that the subsidence of the WAB was controlled by the pull of the dipping subducting lithosphere hence explaining the considerable thickness (10km) of the mostly undeformed sedimentary infill.

The GPlates Portal: Cloud-Based Interactive 3D Visualization of Global Geophysical and Geological Data in a Web Browser.

The pace of scientific discovery is being transformed by the availability of ‘big data’ and open access, open source software tools. These innovations open up new avenues for how scientists communicate and share data and ideas with each other and with the general public. Here, we describe our efforts to bring to life our studies of the Earth system, both at present day and through deep geological time. The GPlates Portal (portal.gplates.org) is a gateway to a series of virtual globes based on the Cesium Javascript library. The portal allows fast interactive visualization of global geophysical and geological data sets, draped over digital terrain models. The globes use WebGL for hardware-accelerated graphics and are cross-platform and cross-browser compatible with complete camera control. The globes include a visualization of a high-resolution global digital elevation model and the vertical gradient of the global gravity field, highlighting small-scale seafloor fabric such as abyssal hills, fracture zones and seamounts in unprecedented detail. The portal also features globes portraying seafloor geology and a global data set of marine magnetic anomaly identifications. The portal is specifically designed to visualize models of the Earth through geological time. These space-time globes include tectonic reconstructions of the Earth’s gravity and magnetic fields, and several models of long-wavelength surface dynamic topography through time, including the interactive plotting of vertical motion histories at selected locations. The globes put the on-the-fly visualization of massive data sets at the fingertips of end-users to stimulate teaching and learning and novel avenues of inquiry.

A synthesis of Jurassic and Early Cretaceous crustal evolution along the southern margin of the Arctic Alaska–Chukotka microplate and implications for defining tectonic boundaries active during opening of Arctic Ocean basins

A synthesis of Late Jurassic and Early Cretaceous collision-related metamorphic events in the Arctic Alaska–Chukotka microplate clarifies its likely movement history during opening of the Amerasian and Canada basins. Comprehensive tectonic reconstructions of basin opening have been problematic, in part, because of the large size of the microplate, uncertainties in the location and kinematics of structures bounding the microplate, and lack of information on its internal deformation history. Many reconstructions have treated Arctic Alaska and Chukotka as a single crustal entity largely on the basis of similarities in their Mesozoic structural trends and similar late Proterozoic and early Paleozoic histories. Others have located Chukotka near Siberia during the Triassic and Jurassic, on the basis of detrital zircon age populations, and suggested that it was Arctic Alaska alone that rotated. The Mesozoic metamorphic histories of Arctic Alaska and Chukotka can be used to test the validity of these two approaches. A synthesis of the distribution, character, and timing of metamorphic events reveals substantial differences in the histories of the southern margin of the microplate in Chukotka in comparison to Arctic Alaska and places specific limitations on tectonic reconstructions. During the Late Jurassic and earliest Cretaceous, the Arctic Alaska margin was subducted to the south, while the Chukotka margin was the upper plate of a north-dipping subduction zone or a zone of transpression. An early Aptian blueschist- and greenschist-facies belt records the most profound crustal thickening event in the evolution of the orogen. It may have resulted in thicknesses of 50–60 km and was likely the cause of flexural subsidence in the foredeep of the Brooks Range. This event involved northern Alaska and northeasternmost Chukotka; it did not involve central and western Chukotka. Arctic Alaska and Chukotka evolved separately until the Aptian thickening event, which was likely a result of the rotation of Arctic Alaska into central and western Chukotka. In northeastern Chukotka, the thickened rocks are separated from the relatively little thickened continental crust of the remainder of Chukotka by the oceanic rocks of the Kolyuchin-Mechigmen zone. The zone is a candidate for an Early Cretaceous suture that separated most of Chukotka from northeast Chukotka and Alaska. Albian patterns of magmatism, metamorphism, and deformation in Chukotka and the Seward Peninsula may represent an example of escape tectonics that developed in response to final amalgamation of Chukotka with Eurasia.

Exhumation history of the Tatry Mountains, Western Carpathians, constrained by low‐temperature thermochronology

AbstractThis study tests alternative models for the growth of the Tatry Mountains (Central Western Carpathians) by the application of low‐temperature thermochronology. Zircon (U + Th)/He ages from the north of the range are mostly between 48 and 37 Ma and indicate cooling prior to the onset of fore‐arc sedimentation in the region (42–39 Ma). In contrast, zircon (U + Th)/He ages in the south of the range are around 22 Ma. Apatite fission track ages across the sampled sites range from 20 to 15 Ma. Apatite (U + Th)/He ages range from 18 to 14 Ma with little variation with elevation or horizontal location. Based on thermal modeling and tectonic reconstructions, these Miocene ages are interpreted as cooling in the hanging wall of a northward dipping thrust ramp in the current location of the sub‐Tatric fault with cooling rates of ~20°C/Myr at ~22–14 Ma. Modeled cooling histories require an abrupt deceleration in cooling after ~14 Ma to &lt;5°C/Myr. This is associated with termination of deformation in the Outer Carpathians and is synchronous with the transition of the Pannonian Basin from a syn‐rift to a postrift stage and with termination of N‐S compression in the northern part of the Central Western Carpathians. Overall, the timing of shortening and exhumation is synchronous with the formation of the Outer Carpathian orogen and so the Miocene exhumation of the Tatry records retrovergent thrusting at the northern margin of the Alcapa microplate.

The Timing of Magmatism and Ore Formation in the El Abra Porphyry Copper Deposit, Northern Chile: Implications for Long-Lived Multiple-Event Magmatic-Hydrothermal Porphyry Systems

Zircon LA-ICP-MS and CA-TIMS and molybdenite Re-Os geochronology for the El Abra porphyry copper deposit (Chile) document a ~8.6 Ma protracted magmatic-hydrothermal history. Initial magmatic events occurred at ~45 Ma, and continued to ~36 Ma. An ~1.8 m.y. magmatic lull is recorded in the early stages of magmatism, which is characterized by equigranular rocks from the Pajonal suite. Magmatism from ~41 to ~36 Ma, corresponding to the El Abra Granodiorite Complex, is more recurrent, ending in a ~1.4 m.y. period of porphyritic intrusions, which are coeval with Cu-Mo mineralization. Late porphyritic units reveal subtle zircon inheritance likely associated with early magmatic pulses. The young stages of magmatism indicate system rejuvenation based on plagioclase phenocryst compositions, suggesting that the porphyry system is ultimately linked to a less evolved magma. Although there are multiple porphyry and veining events, molybdenite Re-Os ages define a focused mineralization episode from 36.34 to 36.18 Ma. Molybdenite Re-Os ages from nearby related prospects belonging to the El Abra cluster expand the mineralization period in the district up to ~1.0 m.y., suggesting a multistage, long-lived hydrothermal system. Integration of the molybdenite Re-Os dates and those from previous works at the El Abra and Toki clusters, accompanied by available tectonic reconstruction along the Domeyko fault system suggest the development, by late Eocene times, of a single, large (~30 km across) porphyry copper cluster, which was subsequently separated by an offset of ~35 km along the West fault.

Crystallization depth beneath an oceanic detachment fault (ODP Hole 923A, Mid‐Atlantic Ridge)

AbstractOceanic detachment faults are increasingly recognized as playing an integral role in the seafloor spreading process at slow and ultraslow spreading mid‐ocean ridges, with significant consequences for the architecture of the oceanic lithosphere. Although melt supply is considered to play a critical control on the formation and evolution of oceanic detachments, much less well understood is how melts and faults interact and influence each other. Few direct constraints on the locus and depth of melt emplacement in the vicinity of detachments are available. Gabbros drilled in ODP Hole 923A near the intersection of the Mid‐Atlantic Ridge and the Kane transform fault (23°N; the MARK area) represent magmas emplaced into the footwall of such a detachment fault and unroofed by it. We here present U‐Pb zircon dates for these gabbros and associated diorite veins which, when combined with a tectonic reconstruction of the area, allow us to calculate the depths at which the melts crystallized. Th‐corrected single zircon U‐Pb dates from three samples range from 1.138 ± 0.062 to 1.213 ± 0.021 Ma. We find a crystallization depth of 6.4 +1.7/−1.3 km, and estimate that the melts parental to the gabbros were initially emplaced up to 1.5 km deeper, at &lt;8 km below the seafloor. The tectonic reconstruction implies that the detachment fault responsible for the exposure of the sampled sequence likely crossed the ridge axis at depth, suggesting that melt emplacement into the footwall of oceanic detachment faults is an important process. The deep emplacement depth we find associated with “detachment mode” spreading at ∼1.2 Ma appears to be significantly greater than the depth of magma reservoirs during the current “magmatic mode” of spreading in the area, suggesting that the northern MARK segment preserves a recent switch between two temporally distinct modes of spreading with fundamentally different lithospheric architecture.

A sequential data assimilation approach for the joint reconstruction of mantle convection and surface tectonics

With the progress of mantle convection modelling over the last decade, it now becomes possible to solve for the dynamics of the interior flow and the surface tectonics to first order. We show here that tectonic data (like surface kinematics and seafloor age distribution) and mantle convection models with plate-like behaviour can in principle be combined to reconstruct mantle convection. We present a sequential data assimilation method, based on suboptimal schemes derived from the Kalman filter, where surface velocities and seafloor age maps are not used as boundary conditions for the flow, but as data to assimilate. Two stages (a forecast followed by an analysis) are repeated sequentially to take into account data observed at different times. Whenever observations are available, an analysis infers the most probable state of the mantle at this time, considering a prior guess (supplied by the forecast) and the new observations at hand, using the classical best linear unbiased estimate. Between two observation times, the evolution of the mantle is governed by the forward model of mantle convection. This method is applied to synthetic 2-D spherical annulus mantle cases to evaluate its efficiency. We compare the reference evolutions to the estimations obtained by data assimilation. Two parameters control the behaviour of the scheme: the time between two analyses, and the amplitude of noise in the synthetic observations. Our technique proves to be efficient in retrieving temperature field evolutions provided the time between two analyses is 10 Myr. If the amplitude of the a priori error on the observations is large (30 per cent), our method provides a better estimate of surface tectonics than the observations, taking advantage of the information within the physics of convection.

Application of detrital zircon U-Pb geochronology to surface and subsurface correlations of provenance, paleodrainage, and tectonics of the Middle Magdalena Valley Basin of Colombia

Detrital zircon U-Pb geochronology has been used extensively to develop provenance histories for surface outcrops of key stratigraphic localities within sedimentary basins. However, many basins lack sufficiently continuous and widespread exposures of complete successions to evaluate proposed long-term tectonic histories, stratigraphic correlations, and paleodrainage patterns within individual basins. Here, we demonstrate the utility of subsurface detrital zircon U-Pb analysis by integrating ages from three key wells (21 subsurface samples) with previously reported data from six exposed intervals (90 surface samples) within a single basin. Samples from the 5-10-km-thick clastic successions span several structural blocks over an similar to 300 x 50 km swath of the Middle Magdalena Valley Basin, a north-trending intermontane basin in the northern Andes of Colombia. Available U-Pb age distributions for modern rivers highlight the distinctive signatures of several competing sediment sources, including two major contiguous ranges (Central Cordillera and Eastern Cordillera) and two localized block uplifts (Santander Massif and San Lucas range). U-Pb results from Jurassic through Neogene stratigraphic units spanning the nine surface and subsurface sites, including several type localities, enable comparisons of provenance shifts at specific sites and spatial variations among key stratigraphic intervals across multiple sites. Distinctive age populations for the Andean magmatic arc, retroarc fold-thrust belt, and South American craton facilitate correlation of stratigraphic units and reconstruction of the long-term provenance and tectonic evolution of the Middle Magdalena Valley Basin. Nearly all surface and subsurface localities show up-section changes in age spectra consistent with (1) Jurassic growth of extensional subbasins fed by local igneous sources, (2) Cretaceous deposition in an extensive postrift setting, and (3) protracted Cenozoic growth of basin-bounding ranges during Andean crustal shortening. Subsurface samples augment surface samples, highlighting their utility in developing regional source-to-sink relationships, the timing of paleodrainage integration, and tectonic reconstructions. Provenance shifts of mid-Paleocene and latest Eocene-earliest Oligocene age are consistent with incipient uplift of the flanking Central Cordillera and Eastern Cordillera, respectively. However, a well-documented phase of latest Paleocene-middle Eocene beveling of basement uplifts in the Middle Magdalena Valley Basin appears to be largely aliased in the detrital record. Moreover, despite the proximity of the magmatic arc, there is insufficient syndepositional evidence for a proposed Paleogene pulse of magmatism and, in this case, limited utility of U-Pb ages in pinpointing precise depositional (stratigraphic) ages. U-Pb age spectra for Oligocene through Pliocene basin fill underscore complex along-strike (north-south) and cross-strike (east-west) variations reflective of compartmentalized transverse deposystems demarcated by point-source contributions from the Central Cordillera and Eastern Cordillera. The late Miocene appearance of 100-0 Ma grains and a regional switch to broad, multimodal age distributions suggest the initial integration of the longitudinal proto-Magdalena River, linking the Middle Magdalena Valley Basin with southern headwaters in the Upper Magdalena Valley and likely driving increased sedimentation rates farther north in the offshore Magdalena submarine fan of the southern Caribbean margin.

A sub-crustal piercing point for North Atlantic reconstructions and tectonic implications

Plate tectonic reconstructions are usually constrained by the correlation of lineaments of surface geology and crustal structures. This procedure is, however, largely dependent on and complicated by assumptions on crustal structure and thinning and the identification of the continent-ocean transition. We identify two geophysically and geometrically similar upper mantle structures in the North Atlantic and suggest that these represent remnants of the same Caledonian collision event. The identification of this structural lineament provides a sub-crustal piercing point and hence a novel opportunity to tie plate tectonic reconstructions. Further, this structure coincides with the location of some major tectonic events of the North Atlantic post-orogenic evolution such as the occurrence of the Iceland Melt Anomaly and the separation of the Jan Mayen microcontinent. We suggest that this inherited orogenic structure played a major role in the control of North Atlantic tectonic processes.

Playing jigsaw with Large Igneous Provinces—A plate tectonic reconstruction of Ontong Java Nui, West Pacific

AbstractThe three largest Large Igneous Provinces (LIP) of the western Pacific—Ontong Java, Manihiki, and Hikurangi Plateaus—were emplaced during the Cretaceous Normal Superchron and show strong similarities in their geochemistry and petrology. The plate tectonic relationship between those LIPs, herein referred to as Ontong Java Nui, is uncertain, but a joined emplacement was proposed by Taylor (2006). Since this hypothesis is still highly debated and struggles to explain features such as the strong differences in crustal thickness between the different plateaus, we revisited the joined emplacement of Ontong Java Nui in light of new data from the Manihiki Plateau. By evaluating seismic refraction/wide‐angle reflection data along with seismic reflection records of the margins of the proposed “Super”‐LIP, a detailed scenario for the emplacement and the initial phase of breakup has been developed. The LIP is a result of an interaction of the arriving plume head with the Phoenix‐Pacific spreading ridge in the Early Cretaceous. The breakup of the LIP shows a complicated interplay between multiple microplates and tectonic forces such as rifting, shearing, and rotation. Our plate kinematic model of the western Pacific incorporates new evidence from the breakup margins of the LIPs, the tectonic fabric of the seafloor, as well as previously published tectonic concepts such as the rotation of the LIPs. The updated rotation poles of the western Pacific allow a detailed plate tectonic reconstruction of the region during the Cretaceous Normal Superchron and highlight the important role of LIPs in the plate tectonic framework.

Neoproterozoic (ca. 820–830 Ma) mafic dykes at Olympic Dam, South Australia: Links with the Gairdner Large Igneous Province

A suite of basaltic to doleritic dykes (named the Olympic Dam dolerite) has been intersected in drill holes at the Olympic Dam iron oxide Cu–U–Au–Ag deposit in the Gawler Craton, South Australia. The dykes intrude the ca. 1600Ma Roxby Downs Granite as well as the Olympic Dam Breccia Complex, and range from several centimetres to over 100m in width, strike NW and dip subvertically. Clinopyroxene and plagioclase are the major minerals, together with accessory apatite and Ti-magnetite. Magmatic apatite crystals in medium-grained doleritic dykes have been dated by LA-ICPMS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry), and yielded a U–Pb age of 825±18Ma. The Olympic Dam dolerite has invariably been altered. Secondary apatite and titanite crystals from post-magmatic veinlets cutting the same dykes give similar results of 821±15Ma and 817±11Ma, respectively. All these results are, within error, coincident in age with the Gairdner Dyke Swarm, the longest dyke swarm (∼1000km in length) in Australia. The Olympic Dam dolerite shows similar compositional trends and variations to the Gairdner Dyke Swarm, especially in terms of the relatively immobile High Field Strength Elements (HFSE) and Rare Earth Element (REE). We conclude that the Olympic Dam dolerite belongs to the Gairdner Dyke Swarm, expanding its known extent and compositional range. The Gairdner Dyke Swarm is a major component of the ca. 820Ma Gairdner Large Igneous Province (LIP) generated during the break-up of the supercontinent Rodinia. The ca. 1070Ma Warakurna and the ca. 820Ma Gairdner LIP in Australia are compositionally distinct, whereas the Gairdner LIP and LIP and mafic suites associated with the break-up of Rodinia in South China and North America are broadly similar. This provides geochemical support for a Gairdner LIP origin for some mafic suites, in particular the Beda Volcanics in South Australia, and for a juxtaposition of South China, South Australia and North America in the tectonic reconstruction of Rodinia at ca. 820Ma.

Stable isotopes and geochemistry of a Campanian–Maastrichtian pelagic succession, Mudurnu–Göynük Basin, NW Turkey: Implications for palaeoceanography, palaeoclimate and sea-level fluctuations

This study focuses on the palaeoclimatic evolution and relative sea-level fluctuations of the northern branch of NeoTethys during the late Campanian–early Danian. The studied succession (İsmailler Section) is located in the Mudurnu–Göynük Basin, NW Turkey and dominated by apparently continuous pelagic muddy deposits. Stable isotopic and elemental compositions of the mudrocks are investigated in order to evaluate the palaeoceanographic conditions as well as broad tectonic reconstruction of the basin. The mudrock geochemistry suggests a tectonic reorganization during late Campanian as reflected by a distinct shift from felsic to mafic sediment provenance. In the İsmailler Section, five δ13C events are identified; four or which are well correlatable with major events in other records around the world, such as the late Campanian Event (LCE), Campanian–Maastrictian Boundary (CMB) and the late Maastrichtian Event (LME). The relative sea-level variations in the basin typically match both short- and long-term global sea-level fluctuations. The remaining globally uncorrelatable δ13C event does coincide with tectonic uplift and the abrupt negative δ13C shift, and is inferred to be the result of regional factors. The dominance of worldwide events in the records of the relatively restricted ocean branch reflects the strength of global factors.

The Palu Metamorphic Complex, NW Sulawesi, Indonesia: Origin and evolution of a young metamorphic terrane with links to Gondwana and Sundaland

The Palu Metamorphic Complex (PMC) is exposed in a late Cenozoic orogenic belt in NW Sulawesi, Indonesia. It is a composite terrane comprising a gneiss unit of Gondwana origin, a schist unit composed of meta-sediments deposited along the SE Sundaland margin in the Late Cretaceous and Early Tertiary, and one or more slivers of amphibolite with oceanic crust characteristics. The gneiss unit forms part of the West Sulawesi block underlying the northern and central sections of the Western Sulawesi Province. The presence of Late Triassic granitoids and recycled Proterozoic zircons in this unit combined with its isotopic signature suggests that the West Sulawesi block has its origin in the New Guinea margin from which it rifted in the late Mesozoic. It docked with Sundaland sometime during the Late Cretaceous. U–Th–Pb dating results for monazite suggest that another continental fragment may have collided with the Sundaland margin in the earliest Miocene. High-pressure (HP) and ultrahigh-pressure (UHP) rocks (granulite, peridotite, eclogite) are found as tectonic slices within the PMC, mostly along the Palu–Koro Fault Zone, a major strike-slip fault that cuts the complex. Mineralogical and textural features suggest that some of these rocks resided at depths of 60–120km during a part of their histories.Thermochronological data (U–Th–Pb zircon and 40Ar/39Ar) from the metamorphic rocks indicate a latest Miocene to mid-Pliocene metamorphic event, which was accompanied by widespread granitoid magmatism and took place in an extensional tectonic setting. It caused recrystallization of, and new overgrowths on, pre-existing zircon crystals, and produced andalusite–cordierite–sillimanite–staurolite assemblages in pelitic protoliths, indicating HT–LP (Buchan-type) metamorphism. The PMC was exhumed as a core complex at moderate rates (c. 0.7–1.0mm/yr) accompanied by rapid cooling in the Plio-Pleistocene. Some of the UHP rocks were transported to the surface at significantly higher rates (⩾16mm/yr).The results of our study do not support recent plate tectonic reconstructions that propose a NW Australia margin origin for the West Sulawesi block (e.g. Hall et al., 2009).