Applying Boundary Element Simulation to Generate Stress-Based Fracture Drivers: A Case Study for the Montney Unconventional Oil/Gas Play in Western Canada Basin

Natural fracture distribution is critical to the hydrocarbon production from the Early Triassic Montney unconventional oil and gas play. The formation underwent several tectonic events, creating a unique natural fracture system. Identifying tectonic events and their stress field evolution is an import component in fracture system modeling and prediction. The objective of this paper is to identify the evolution of paleo-stress domains, to establish related tectonic models, and to generate the drivers for fracture network modeling which will aid in reservoir understanding and overall play development. Compared with other geomechanical approaches, the boundary element method (BEM) is better suited for the structural characteristics in the study area. Hence, the corresponding boundary element simulation (BES) was applied for the evolution of the paleo-stress domains. The methodology is a combination of 3D BEM and Monte Carlo simulations. The inputs include seismic interpreted faults and natural fractures from Formation Microimager logs. After applying the methodology, several best fit realizations were calculated, and the admissible paleo-stress domains were characterized by the tectonic models which are consistent with the regional tectonic evolution of the formation. The study area is about 400 km2 located at northeast British Columbia in the Western Canada Basin. The main structural features are the thrust and back-thrust faults, forming different fault blocks without any significant deformation structures. The Montney formation within the study area underwent several tectonic events: (1) regime of terrane collision, indentation and lateral escape during end of Middle Jurassic to Middle Cretaceous; (2) regime of left-lateral transpression dominated by strike-slip during end of Late Cretaceous and Paleocene; and (3) regime of right-lateral transtension dominated by strike-slip during end of Early and Middle Eocene which is maintained till present day. Three major stress domains were identified in the study area by the application of the BES method, one reverse event and two strike-slip events, representing paleo and present-day stress domains. These stress domains are consistent with the regional tectonic evolution history of the foreland basin. The stress field parameters, such as stress ratio and maximum horizontal stress azimuth, are consistent. The derived tectonic models are shown to be reliable drivers for the subsequent fracture modeling and geomechanics study.

Eocene to Miocene tectonostratigraphic evolution of northwest New Zealand

<p>Reinga Basin is located northwest of New Zealand, along strike structurally from Northland and has a surface area of ~150,000 km². The basin contains deformed Cretaceous and Cenozoic strata, flat unconformities interpreted as sea level-modulated erosion surfaces and is intruded by volcanics. Persistent submarine conditions and moderate water depths has led to preservation of fossil-rich bathyal sedimentary records. This thesis presents the first seismic-stratigraphic analysis tied to dredged rock samples and recent International Ocean Discovery Program (IODP) drilling. The Cenozoic tectonic evolution of Reinga Basin comprises four main phases. (1) Folding and uplift from lower bathyal water depths occurred at 56-43 Ma along West Norfolk Ridge to produce wave ravinement surfaces. This phase of deformation in Reinga Basin pre-dates tectonic events onshore New Zealand. (2) Basin-wide 39-34 Ma compression and reverse faulting exposed early to middle Eocene strata at the seabed. This phase of deformation is also observed farther south in Taranaki. (3) Oligocene uplift is recorded by late Oligocene shallow-water fauna at Site U1508, and led to a 6 Myr hiatus (34-28 Ma) associated with flat wave ravinement surfaces nearby. The unconformity is temporally associated with: normal faulting near West Norfolk Ridge that created topography of Wanganella Ridge; onset of Reinga Basin volcanism; and emplacement of South Maria Allochthon. Thin-skinned deformation and volcanism post-date thick-skinned reverse faulting and folding. The end of reverse faulting near South Maria Ridge is determined from undeformed Oligocene strata that have subsided 1500-2000 m since 36-30 Ma. (4) During the final phase of Reinga Basin deformation, South Maria Ridge subsided ~900-1900 m from middle shelf to bathyal depths from 23-19 Ma. Deformation migrated southeastwards, culminating in Northland Allochthon emplacement (23-20 Ma) and onshore arc volcanism at 23-12 Ma. Eocene onset of tectonic activity in northern New Zealand is shown to be older than previously recognised and it was broadly synchronous with other events related to subduction initiation and plate motion change elsewhere in the western Pacific.</p>

Eocene to Miocene tectonostratigraphic evolution of northwest New Zealand

<p>Reinga Basin is located northwest of New Zealand, along strike structurally from Northland and has a surface area of ~150,000 km². The basin contains deformed Cretaceous and Cenozoic strata, flat unconformities interpreted as sea level-modulated erosion surfaces and is intruded by volcanics. Persistent submarine conditions and moderate water depths has led to preservation of fossil-rich bathyal sedimentary records. This thesis presents the first seismic-stratigraphic analysis tied to dredged rock samples and recent International Ocean Discovery Program (IODP) drilling. The Cenozoic tectonic evolution of Reinga Basin comprises four main phases. (1) Folding and uplift from lower bathyal water depths occurred at 56-43 Ma along West Norfolk Ridge to produce wave ravinement surfaces. This phase of deformation in Reinga Basin pre-dates tectonic events onshore New Zealand. (2) Basin-wide 39-34 Ma compression and reverse faulting exposed early to middle Eocene strata at the seabed. This phase of deformation is also observed farther south in Taranaki. (3) Oligocene uplift is recorded by late Oligocene shallow-water fauna at Site U1508, and led to a 6 Myr hiatus (34-28 Ma) associated with flat wave ravinement surfaces nearby. The unconformity is temporally associated with: normal faulting near West Norfolk Ridge that created topography of Wanganella Ridge; onset of Reinga Basin volcanism; and emplacement of South Maria Allochthon. Thin-skinned deformation and volcanism post-date thick-skinned reverse faulting and folding. The end of reverse faulting near South Maria Ridge is determined from undeformed Oligocene strata that have subsided 1500-2000 m since 36-30 Ma. (4) During the final phase of Reinga Basin deformation, South Maria Ridge subsided ~900-1900 m from middle shelf to bathyal depths from 23-19 Ma. Deformation migrated southeastwards, culminating in Northland Allochthon emplacement (23-20 Ma) and onshore arc volcanism at 23-12 Ma. Eocene onset of tectonic activity in northern New Zealand is shown to be older than previously recognised and it was broadly synchronous with other events related to subduction initiation and plate motion change elsewhere in the western Pacific.</p>

Time-Series Analysis of Crustal Deformation on Longstanding Transcurrent Fault: Structural Diversity along Median Tectonic Line, Southwest Japan, and Tectonic Implications

The Median Tectonic Line (MTL) along the longstanding convergent margin of eastern Eurasia has been activated intermittently since ca. 100 Ma. In its incipient phase, propagating strike slips on the MTL generated an elongate pull-apart depression buried by voluminous clastics of the Late Cretaceous Izumi Group. In this study, the complicated deformation processes around this regional arc-bisecting fault are unraveled through a series of quantitative analyses. Our geological survey of the Izumi Group was exclusively conducted in an area of diverse fault morphology, such as jogs and steps. The phase stripping method was introduced to elucidate the time sequence of cumulative tectonic events. After stripping away the initial structure related to basin formation, neotectonic signatures were successfully categorized into discrete clusters originating from progressive wrenching near the active MTL fault system, which has been reactivated by the Quaternary oblique subduction of the Philippine Sea Plate. The method presented here is simple and effective for the detection and evaluation of active crustal failures in mobile belts where records of multiphase architectural buildup coexist.

Timing and kinematics of the Variscan orogenic cycle at the Moldanubian periphery of the central Bohemian Massif

The high-grade complexes along the northern Moldanubian periphery of the central Bohemian Massif provide an outstanding structural record of all episodes of the Variscan collisional evolution. Kinematics and timing of orogenic processes have been examined by structural and microstructural study of middle and lower crustal rocks combined with xenotime and monazite geochronology. Four distinct tectonic events have been identified in the studied units. A first relict sub-horizontal fabric S1 associated with the HP/HT metamorphism is developed only in the lower crustal rocks and was related to back-arc extension or lower crustal flow in a supra-subduction domain. This fabric was at c. 340 Ma completely reworked to the sub-vertical foliation S2 by the major collisional thickening leading to the lower and middle crust juxtaposition. Thereafter, the extensional collapse of thickened orogenic system caused strong refolding to the HT sub-horizontal fabric at c. 325 Ma. The region was subsequently affected by the NNE–SSW oriented horizontal shortening related to the dextral shearing and clockwise rotation of crustal blocks adjacent to the large scale dextral shear zone, the Elbe Zone. It led to the fragmentation and reorientation of the Moldanubian margin to the current position.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5708800.v1

Recalibrating the Devonian time scale: A new method for integrating radioisotopic and astrochronologic ages in a Bayesian framework

The numerous biotic, climatic, and tectonic events of the Devonian cannot be correlated and investigated without a well-calibrated time scale. Here, we updated the calibration of the Devonian time scale using a Bayesian age-depth model that incorporates radioisotopic ages and astrochronology durations. We used existing radioisotopic ages collected and harmonized in the last two geologic time scale compilations, as well as new U-Pb zircon ages from Emsian {Hercules I K-bentonite, Wetteldorf, Germany: 394.290 ± 0.097(0.21)[0.47] Ma} and Eifelian K-bentonites {Tioga B and Tioga F K-bentonites, Fayette, New York, USA: 390.82 ± 0.18(0.26)[0.48] Ma and 390.14 ± 0.14(0.23)[0.47] Ma, respectively}. We anchored floating astrochronology stage durations on radioisotopic ages and chained astrochronologic constraints and uncertainty together to extrapolate conditioning age likelihoods up or down the geologic time scale, which is a new method for integrating astrochronology into age-depth modeling. The modeling results in similar ages and durations for Devonian stages regardless of starting biostratigraphic scaling assumptions. We produced a set of rescaled biostratigraphic zonations, and a new numerical calibration of Devonian stage boundary ages with robust uncertainty estimates, which allow us to evaluate future targets for Devonian time scale research. These methods are broadly applicable for time scale work and provide a template for an integrated stratigraphic approach to time scale modeling.

Metamorphism and the P-T History of Alpine Schist from the Newton Range, Southern Alps, New Zealand

<p>Metamorphic rocks have the potential to record in their mineral assemblages, mineral compositional zoning, and textures, information about geological changes and processes that occur during tectonic events. Interpretations of metamorphic pressure-temperature (P-T) records have traditionally relied on results of geothermobarometry studies, but that approach is not suitable in every case. Metamorphosed greywacke, which makes up ~95% of the New Zealand Southern Alps, has long proven problematic for traditional geothermobarometry because it develops intractable mineral compositions and/or assemblages, especially at relatively low temperature (greenschist facies) conditions. An alternative forward modelling approach using the computer program THERMOCALC was recently used to extract the first detailed P-T history (P-T path) from such previously intractably difficult "greyschist" rocks from a single site in the New Zealand Southern Alps. The present study is the first attempt to apply those new methods to rocks from another study area, and is the first detailed geological study of the Newton Range in the New Zealand Southern Alps. The Newton Range is a ~15 km-long, east-west trending range located ~30 km southeast of the town of Hokitika, ~110 km northeast of the Franz Josef-Fox Glacier region, and immediately to the east of the Alpine Fault in the Southern Alps, South Island, New Zealand. The rocks in the Newton Range are mainly derived from Torlesse Terrane accretionary prism greywacke and argillite (Alpine Schist, greyschist), together with a large pods of ultramafic rock (part of the Pounamu Ultramafic Belt (PUB)) and minor associated metabasic layers (greenschist), all metamorphosed to greenschist facies conditions. The dominant mineral assemblage in the greyschist (Qtz + Ms+ Bt ± Chl ± Ep ± Pl ± Ilm ± Ttn ± Grt ± Zrn ± Tur ± Ap ± Cal), much like that found elsewhere in the Southern Alps. As elsewhere in the Southern Alps, the dominant high-grade metamorphic mineral assemblages in the Alpine Schist in the Newton Range are inherited. The mineral assemblages, compositions, and some textures thus record evidence of processes that took place during tectonic events, presumably mainly in Cretaceous time, prior to the formation of the modern Southern Alps, which are forming today by the ongoing oblique continent-continent collision of the Pacific Plate against the Australian Plate at the Alpine Fault. Compositional zoning in garnet from the greyschist is an important record of the metamorphic P-T path traversed by the host rock as the garnet grew. Occasionally, garnet from the study area contains an inmost core (stage 0) of unusual (anomalously high- or low-MnO) composition. The cores with extremely low MnO are possibly detrital in origin, and those with extremely high MnO may perhaps have grown in the early tectonic episode that formed the Otago Schist. Typically, garnet shows the following core- to rim zoning sequence. Stages 1 & 2 show a progressive decrease in MnO and increase in FeO from core to rim, with higher MnO cores present in rocks with higher whole-rock MnO compositions. Stage 3 is characterised by a gradual decrease in CaO and signifies the growth of Ca-bearing oligoclase late in the garnet growth history. Stage 4 is a discontinuous overgrowth characterised by an abrupt increase in CaO. Such overgrowths have in the past been attributed to garnet growth accompanying the development of the Alpine Fault mylonite zone in the late Cenozoic. In the Newton Range they were only observed on garnet adjacent to the main outcrop of the PUB at ~4.5km from the Alpine Fault, far from the mylonite zone, so local element availability during decompression (and possibly fluid flow and/or metasomatism) may have played a part in the growth of these rims. A P-T path for Alpine Schist from the Newton Range has been estimated using detailed garnet composition data measured along core-to-rim transects across individual garnets, together with predicted garnet compositions and P-T pseudosection results calculated using THERMOCALC. The P-T path starts at ~3.5kbar/400°C, where both garnet and albite coexist, and increases in pressure and temperature to ~6.5bar/500°C where garnet coexists with both albite and oligoclase. The estimated peak metamorphic conditions probably correspond to peak metamorphic pressures, unlike in the Franz Josef-Fox Glacier region where peak conditions (~9.2kbar and 620°C) probably coincided with peak metamorphic temperatures.</p>

Metamorphism and the P-T History of Alpine Schist from the Newton Range, Southern Alps, New Zealand

<p>Metamorphic rocks have the potential to record in their mineral assemblages, mineral compositional zoning, and textures, information about geological changes and processes that occur during tectonic events. Interpretations of metamorphic pressure-temperature (P-T) records have traditionally relied on results of geothermobarometry studies, but that approach is not suitable in every case. Metamorphosed greywacke, which makes up ~95% of the New Zealand Southern Alps, has long proven problematic for traditional geothermobarometry because it develops intractable mineral compositions and/or assemblages, especially at relatively low temperature (greenschist facies) conditions. An alternative forward modelling approach using the computer program THERMOCALC was recently used to extract the first detailed P-T history (P-T path) from such previously intractably difficult "greyschist" rocks from a single site in the New Zealand Southern Alps. The present study is the first attempt to apply those new methods to rocks from another study area, and is the first detailed geological study of the Newton Range in the New Zealand Southern Alps. The Newton Range is a ~15 km-long, east-west trending range located ~30 km southeast of the town of Hokitika, ~110 km northeast of the Franz Josef-Fox Glacier region, and immediately to the east of the Alpine Fault in the Southern Alps, South Island, New Zealand. The rocks in the Newton Range are mainly derived from Torlesse Terrane accretionary prism greywacke and argillite (Alpine Schist, greyschist), together with a large pods of ultramafic rock (part of the Pounamu Ultramafic Belt (PUB)) and minor associated metabasic layers (greenschist), all metamorphosed to greenschist facies conditions. The dominant mineral assemblage in the greyschist (Qtz + Ms+ Bt ± Chl ± Ep ± Pl ± Ilm ± Ttn ± Grt ± Zrn ± Tur ± Ap ± Cal), much like that found elsewhere in the Southern Alps. As elsewhere in the Southern Alps, the dominant high-grade metamorphic mineral assemblages in the Alpine Schist in the Newton Range are inherited. The mineral assemblages, compositions, and some textures thus record evidence of processes that took place during tectonic events, presumably mainly in Cretaceous time, prior to the formation of the modern Southern Alps, which are forming today by the ongoing oblique continent-continent collision of the Pacific Plate against the Australian Plate at the Alpine Fault. Compositional zoning in garnet from the greyschist is an important record of the metamorphic P-T path traversed by the host rock as the garnet grew. Occasionally, garnet from the study area contains an inmost core (stage 0) of unusual (anomalously high- or low-MnO) composition. The cores with extremely low MnO are possibly detrital in origin, and those with extremely high MnO may perhaps have grown in the early tectonic episode that formed the Otago Schist. Typically, garnet shows the following core- to rim zoning sequence. Stages 1 & 2 show a progressive decrease in MnO and increase in FeO from core to rim, with higher MnO cores present in rocks with higher whole-rock MnO compositions. Stage 3 is characterised by a gradual decrease in CaO and signifies the growth of Ca-bearing oligoclase late in the garnet growth history. Stage 4 is a discontinuous overgrowth characterised by an abrupt increase in CaO. Such overgrowths have in the past been attributed to garnet growth accompanying the development of the Alpine Fault mylonite zone in the late Cenozoic. In the Newton Range they were only observed on garnet adjacent to the main outcrop of the PUB at ~4.5km from the Alpine Fault, far from the mylonite zone, so local element availability during decompression (and possibly fluid flow and/or metasomatism) may have played a part in the growth of these rims. A P-T path for Alpine Schist from the Newton Range has been estimated using detailed garnet composition data measured along core-to-rim transects across individual garnets, together with predicted garnet compositions and P-T pseudosection results calculated using THERMOCALC. The P-T path starts at ~3.5kbar/400°C, where both garnet and albite coexist, and increases in pressure and temperature to ~6.5bar/500°C where garnet coexists with both albite and oligoclase. The estimated peak metamorphic conditions probably correspond to peak metamorphic pressures, unlike in the Franz Josef-Fox Glacier region where peak conditions (~9.2kbar and 620°C) probably coincided with peak metamorphic temperatures.</p>

Meso-Cenozoic Exhumation of the Linqing Sub-Basin, Bohai Bay Basin: Implications for Cratonic Destruction

The relationship between the tectonic event of the Linqing Sub-basin and the destruction of the North China Craton (NCC) is an important factor to consider when studying geodynamic mechanisms in eastern China. In the current study, we present a low-temperature apatite thermochronological analysis of 14 samples to study the tectonic event of the Linqing Sub-basin. Our data showed that the apatite fission track (AFT) ages were in the range of 53.5–124.4 Ma, and the average track lengths were 8.00–11.24 μm. The grain ages showed that 10 samples had mixed ages and were characterized by discordant distribution. The minimum ages decomposed from AFT ages mainly ranged from 105.3 to 40.8 Ma. We identified a break-in-slope from the depth-minimum age profile, which was related to the Meso-Cenozoic tectonic event. The AFT age data could be decomposed into three age groups, namely, P3 (394.8–215.7 Ma), P2 (124.6–83.4 Ma), and P1 (70.7–40.8 Ma), indicating three significant tectonic events in the NCC. P3 is related to the uplift of the NCC at 445.0–315.0 Ma and deformation and magmatism at 320.0–200.0 Ma. P2 corresponds to the Mesozoic tectonic activities, such as the closure of the Mongol–Okhotsk Ocean, the turning of the Izanagi plate and mantle convection. P1 mainly corresponds to the Izanagi–Pacific ridge, the closure of the Tethys Ocean, and the rotation of the Philippine Sea plate in the Cenozoic. Our study provides evidence for the destruction of the NCC, and has significance for the understanding of the deep mechanism.