We first describe the methodology for a two-dimensional, elastic deformable microplate modeling approach for continental plate boundaries. Deformable microplate models combine discrete slip on microplate boundaries (faults) with continuous deformation in block interiors. Two idealized models simulating continental collision are presented, one with two microplates and one with four microplates. / Earth and Planetary Sciences

The Central Cordillera and Eastern Cordillera of the northern Andes form the western and eastern flanks of the north-trending Middle Magdalena Valley basin. Previous estimates for the timing of initial exhumation of the two cordilleras range from ~100 to ~10 Ma. Accurately constraining the spatial and temporal distribution of deformation in Colombia has implications for the shortening history of the Andean convergent margin and the prediction of rapid lateral facies changes in sedimentary basins in close proximity to sediment sources. This study applies sandstone petrographic point counts, field sedimentological analyses of basin fill, and paleocurrent measurements of trough cross-stratification, clast imbrication, and flute casts to provide new insights into the tectonic history of the flanks of the Middle Magdalena Valley basin. Between the lower and upper Paleocene strata of the Lisama Formation, paleocurrent orientations show a shift from northward to eastward transport. This change in sediment dispersal coincides with a shift from a cratonic (Amazonian) to orogenic (Andean) sediment source, as recorded by published U-Pb detrital zircon geochronological results (Nie et al. 2010), suggesting initial uplift of the Central Cordillera by mid-Paleocene time. Later in the basin’s history, establishment of an alluvial-plain system with meandering-channel deposits is recorded in lower–middle Eocene strata of the lower La Paz Formation. Consistent eastward paleocurrents characterize mid-Paleocene through uppermost Eocene strata, indicating a continuous influence of western sediment source areas. However, within the upper middle Eocene succession (~40 Ma), at the boundary between the lower and upper La Paz Formation, sandstone compositions show a dramatic decrease in lithic content. This compositional change is accompanied by a facies shift to amalgamated fluvial channels, reflecting changes in both the composition and proximity of the western sediment source. We attribute these changes to the growing influence of the exhumed La Cira/Infantas paleohighs off the western flank of the present-day Nuevo Mundo syncline. In the uppermost Eocene strata of the Esmeraldas Formation, paleocurrents show a switch to dominantly westward transport that persisted through the Neogene. In addition, deposits show a contemporaneous decrease in the amount of coarse-grained channel deposits. These changes are interpreted to reflect the onset of exhumation in the Eastern Cordillera. The lack of a significant change in sandstone compositions at this boundary suggests a compositional similarity between strata uplifted by the Lisama structure and the Eastern Cordillera. These data support and further refine previous thermochronologic and provenance studies which suggest that uplift-induced exhumation of the Central Cordillera and Eastern Cordillera commenced by mid-Paleocene and late Eocene–early Miocene time, respectively. / text

Not available / text

No description available.

No description available.

No description available.

This study investigates evidence for linkages and fault interactions centred on the Cust Anticline in Northwest Canterbury between Starvation Hill to the southwest and the Ashley and Loburn faults to the northeast. An integrated programme of geologic, geomorphic, paleo-seismic and geophysical analyses was undertaken owing to a lack of surface exposures and difficulty in distinguishing active tectonic features from fluvial and/or aeolian features across the low-relief Canterbury Plains. LiDAR analysis identified surface expression of several previously unrecognised active fault traces across the low-relief aggradation surfaces of the Canterbury Plains. Their presence is consistent with predictions of a fault relay exploiting the structural mesh across the region. This is characterised by interactions of northeast-striking contractional faults and a series of re-activating inherited Late Cretaceous normal faults, the latter now functioning as E–W-striking dextral transpressive faults. LiDAR also allowed for detailed analysis of the surface expression of individual faults and folds across the Cust Anticline contractional restraining bend, which is evolving as a pop-up structure within the newly established dextral shear system that is exploiting the inherited, now re-activated, basement fault zone. Paleo-seismic trenches were located on the crest of the western arm of the Cust Anticline and across a previously unrecognised E–W-striking fault trace, immediately southwest of the steeply plunging Cust Anticline termination. These studies confirmed the location and structural style of north-northeast-striking faults and an E–W-striking fault associated with the development of this structural culmination. A review of available industry seismic reflection lines emphasised the presence of a series of common structural styles having the same underlying structural drivers but with varying degrees of development and expression, both in the seismic profiles and in surface elevations across the study area. Based on LiDAR surface mapping and preliminary re-analysis of industry seismic reflection data, four fault zones are identified across the restraining bend structural culminations, which together form the proposed Oxford–Cust–Ashley Fault System. The 2010–2012 Canterbury Earthquake Sequence showed many similarities to the structural pattern established across the Oxford–Cust–Ashley Fault System, emphasising the importance of identification and characterization of presently hidden fault sources, and the understanding of fault network linkages, in order to improve constraints on earthquake source potential. Improved understanding of potentially-interactive fault sources in Northwest Canterbury, with the potential for combined initial fault rupture and spatial and temporal rupture propagation across this fault system, can be used in probabilistic seismic hazard analysis for the region, which is essential for the suitability and sustainability of future social and economic development.

This dissertation research addresses the tectonism of continental crust during ocean basin closure, suturing between continental landmasses, and collisional orogenesis. The new data and insights presented here were gathered through localized geologic investigations of the Tibetan Plateau of central Asia. This area of central Asia is an ideal location to study these fundamental tectonic processes because it has been the locus of numerous Tethyan ocean basins and terminal collisions between continents during Phanerozoic accretion of Gondwana-derived landmasses onto the southern margin of Eurasia. In this work, I propose, in many orogens, that high-pressure (HP) metamorphism of continental rocks may mark the early stages of the suturing process between continental landmasses rather than the culmination of suturing. This insight has been acquired from a geologic-, geochronologic-, and thermochronologic-based investigation of the HP-near ultrahigh-pressure bearing Triassic metasedimentary metamorphic belt in central Tibet. This work shows near synchronous continent-continent collisions between landmass adjacent to the Paleo-Tethys ocean prior to its final closure in Late Triassic time. In addition, this work shows that Mediterranean-style tectonics may be more widespread during accretionary tectonics than previously thought. A comparison between the distribution of the HP bearing metamorphic belt, autochthonous crystalline basement, and geophysical images of Tibet suggests that a Mesozoic tectonic feature may be controlling the structure and distribution of melt within the middle crust of the Tibetan Plateau. This concept underscores the importance of inherited tectonic frameworks on the evolution of orogenic plateaus. Work in southwest Tibet, along the India-Asia suture zone, highlights the complex behavior of continental crust during collisional orogenesis. This work identifies previously undocumented magmatism, crustal antexis, and high-grade metamorphism along the India-Asia suture. In this work I attribute these observations to the initial interactions between Indian, Asian, and subducting Neo-Tethys oceanic lithosphere.

The Atnarko complex located in west-central British Columbia comprises pre-Early Jurassic metavolcanic and metasedimentary rocks, termed the Atnarko assemblage, which is structurally interleaved with Late Triassic to Early Cretaceous orthogneiss. The Atnarko assemblage correlates with continental margin assemblages found within the Coast plutonic complex. Tectonic interaction between the Insular and Intermontane superterranes resulted in several phases of deformation including; 1) poorly preserved Jurassic deformation, 2) Early to mid-Cretaceous, southwest to west directed, compression, 3) mid-Cretaceous, north to northeast directed, compression, 4) mid- to Late Cretaceous dextral and sinistral ductile/brittle shearing, and 5) post latest Cretaceous brittle faulting. Peak metamorphism coincides with generation of migmatite in the Early Cretaceous (~117-115 Ma) and is contemporaneous with penetrative ductile fabrics. The Atnarko complex had cooled below 350°C by the Late. Comparison of the Atnarko complex to equivalent portions of the orogen along strike, indicates a post mid-Cretaceous change in structural style. To the northwest the orogen records continued southwest-directed compression which dominates the deformation style; while to the southeast large dextral strike-slip faults dominate. Relative plate motions between ca. 70-60 Ma indicate that dextral transpression occurred between the Kula and North American plates. Strain during this transpressive deformation was partitioned into compressive and translational regions. The Atnarko complex area is situated at the transition between translation and compression. The conditions of the lower and middle crust within the orogen were established by how strain was partitioned across the orogen. The distributed strain also shaped how the orogen responded to Tertiary extension. Continued compression to the northwest of the Atnarko complex led to increased crustal thickness and partial melting of lower and middle crust in the Tertiary. Conversely, the cessation of compression in the southeast lead to a more stable (i.e. cooler) crustal lithosphere. A change in relative plate motions in the early Tertiary triggered full-scale, orogen-perpendicular, collapse in the northwest facilitated by decoupling between the middle and lower crusts along thermally weakened layers. Localized orogen-parallel extension occurred in the southeast which was kinematically linked to large dextral strike-slip faults where the upper crust remained coupled to the middle and lower crust.

No description available.