Exploring the emplacement of Cretaceous arc granites and dextral shear zones in northwestern Nevada, USA, using the StraboSpot data system

2021 ◽  
pp. 221-251
Author(s):  
S.F. Trevino* ◽  
B. Tikoff ◽  
N. Van Buer ◽  
S.J. Wyld ◽  
H. McLachlan
Keyword(s):  
Solid State ◽  
Shear Zone ◽  
Shear Zones ◽  
Power Line ◽  
Field Trip ◽  
Data System ◽  
Intrusive Complex ◽  
Dextral Shear ◽  
Magnetic Lineations ◽  
Intrusive Suite

ABSTRACT This field trip traverses the Sahwave and Nightingale Ranges in central Nevada, USA, and northward to Gerlach, Nevada, to the Granite, northern Fox, and Selenite Ranges. Plutonic bodies in this area include the ca. 93–89 Ma Sahwave nested intrusive suite of the Sahwave and Nightingale Ranges, the ca. 106 Ma Power Line intrusive complex of the Nightingale Range, the ca. 96 Ma plutons in the Selenite Range, and the ca. 105–102 Ma plutons of the Granite and Fox Ranges. Collectively these plutons occupy nearly 1000 km2 of bedrock exposure. Plutons of the Sahwave, Nightingale, and Selenite Ranges intrude autochthonous rocks east of the western Nevada shear zone, while plutons of the Granite and Fox Ranges intrude displaced terranes west of the western Nevada shear zone. Integrated structural, geochemical, and geochronological studies are used to better understand magmatic and deformation processes during the Early Cretaceous, correlations with Cretaceous plutons in adjacent areas of Idaho and California, and regional implications. Field-trip stops in the Sahwave and Nightingale Ranges will focus on: (1) microstructure and orientation of magmatic and solid-state fabrics of the incrementally emplaced granodiorites-granites of the Sahwave intrusive suite; and (2) newly identified dextral shear zones hosted within intrusions of both the Sahwave and Nightingale Ranges. The Sahwave intrusive suite exhibits moderate to weak magnetic fabrics determined using anisotropy of magnetic susceptibility, with magnetic foliations that strike NW-NE and magnetic lineations that plunge moderately to steeply. Microstructural analysis indicates that these fabrics formed during magmatic flow. The older Power Line intrusive complex in the Nightingale Range is cross-cut by the Sahwave suite and contains a N-S–trending solid-state foliation that reflects ductile dextral shearing. Field-trip stops in the plutons of the Gerlach region will focus on composition, texture, and emplacement ages, and key differences with the younger Sahwave suite, including lack of evidence for zoning and solid-state fabrics. The field trip will utilize StraboSpot, a digital data system for field-based geology that allows participants to investigate the relevant data projects in the study areas.

On the dextral offset of a Variscan shear zone across the Mérens fault in the central Pyrenees (Andorra, France)

2014 ◽  
Vol 185 (2) ◽  
pp. 131-143 ◽  
Author(s):  
Bas van den Eeckhout ◽  
Hans de Bresser
Keyword(s):  
Shear Zone ◽  
Geographical Location ◽  
Structural Data ◽  
Shear Zones ◽  
Fault Activity ◽  
Horizontal Movement ◽  
Tectonic Significance ◽  
Dextral Shear ◽  
North And South ◽  
Central Pyrenees

AbstractThis paper contributes to the understanding of the offset on the 80 km long E-W striking Mérens fault in the central Pyrenees. Parameters such as amount and sense of offset are a prerequisite for a better understanding of the evolution of the fault, its tectonic significance and for reconstruction of the pre-existing configuration of its wall rocks.In the western Aston massif, north of the Mérens fault, an over 5 km long, N125E striking steep dextral shear zone occurs. This shear zone is characterized by medium-grade assemblages of metamorphic minerals and is considered to be of late Variscan age. The presence of such a shear zone in this area was deduced from i) published structural data on the Mérens fault, and ii) its cut off relation with an over 40 km long late Variscan shear zone to the south. In this study it is shown that the shear zones north and south of the Mérens fault initially formed a single late Variscan shear zone, cut and displaced by the younger Mérens fault. The exact geographical location of the shear zone in the Aston massif constrains the finite dextral horizontal movement on the Mérens fault to at least 10,4 ± 0,5 km. Finite uplift of the Aston massif exceeds 4 km. Extrapolation of the arguments to the eastern Aston and Hospitalet massifs indicates that the NE terminations of both gneiss cores also lined up along one single steep (W)NW striking shear zone prior to Mérens fault activity. Dextral horizontal offset is 8,5 ± 1 km in that area. Restoration of the late Variscan configuration of the Aston and Hospitalet massifs reveals an elongate WNW trending mantled gneiss antiform, bordered by steep dextral shear zones with similar trend.

scholarly journals Whole-lithosphere shear during oblique rifting

Geology ◽  
2021 ◽  
Author(s):  
Brandon M. Lutz ◽  
Gary J. Axen ◽  
Jolante W. van Wijk ◽  
Fred M. Phillips
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Shear Zones ◽  
Death Valley ◽  
Necessary Condition ◽  
Middle Crust ◽  
Metamorphic Core Complexes ◽  
Dextral Shear ◽  
Depth Gradients ◽  
Metamorphic Core

Processes controlling the formation of continental whole-lithosphere shear zones are debated, but their existence requires that the lithosphere is mechanically coupled from base to top. We document the formation of a dextral, whole-lithosphere shear zone in the Death Valley region (DVR), southwest United States. Dextral deflections of depth gradients in the lithosphere-asthenosphere boundary and Moho are stacked vertically, defining a 20–50-km-wide, lower lithospheric shear zone with ~60 km of shear. These deflections underlie an upper-crustal fault zone that accrued ~60 km of dextral slip since ca. 8–7 Ma, when we infer that whole-lithosphere shear began. This dextral offset is less than net dextral offset on the upper-crustal fault zone (~90 km, ca. 13–0 Ma) and total upper-crustal extension (~250 km, ca. 16–0 Ma). We show that, before ca. 8–7 Ma, weak middle crust decoupled upper-crustal deformation from deformation in the lower crust and mantle lithosphere. Between 16 and 7 Ma, detachment slip thinned, uplifted, cooled, and thus strengthened the middle crust, which is exposed in metamorphic core complexes collocated with the whole-lithosphere shear zone. Midcrustal strengthening coupled the layered lithosphere vertically and therefore enabled whole-lithosphere dextral shear. Where thick crust exists (as in pre–16 Ma DVR), midcrustal strengthening is probably a necessary condition for whole-lithosphere shear.

scholarly journals Tectonic inversion of compressional structures in the Southern portion of the Paramirim Corridor, Bahia, Brazil

2015 ◽  
Vol 45 (4) ◽  
pp. 541-567 ◽  
Author(s):  
Simone Cerqueira Pereira Cruz ◽  
Fernando Flecha Alkmim ◽  
Johildo Salomão Figueiredo Barbosa ◽  
Ivo Dussin ◽  
Luiz César Corrêa Gomes
Keyword(s):  
Stress Field ◽  
Gravitational Collapse ◽  
Shear Zones ◽  
White Mica ◽  
Tectonic Inversion ◽  
Dextral Shear ◽  
Intrusive Suite ◽  
Extensional Structures

The Paramirim Corridor represents the maximum inversion zone of the Paramirim Aulacogen. Reverse-to-reverse dextral shear zones and various types of folds dominate such corridor. These structures reflect a stress field that is WSW-ENE oriented, developed in units of Aulacogen basement, as well as in the Lagoa Real Intrusive Suite, of Statherian age, in Espinhaço and São Francisco supergroups, of Statherian-Tonian and Cryogenian ages, respectively, and in the Macaúbas-Santo Onofre Group, of Tonian age at the most. A rich collection of extensional structures truncate compressional structures of the Paramirim Corridor, characterized by normal shear zones and foliation, which is sometimes mylonitic, down-dip stretching lineation, drag folds, traction fractures and S/C structures. In these shear zones, quartz occurs truncated by the foliation, while feldspars are fractured and altered to white mica. Distribution of the quartz c-axes is at a maximum of 14° from the Z-axis. Thus, it suggests that the deformation activated mainly the basal glide planes in the <a> direction. The paleostress study using the Win-Tensor software demonstrated that the regimen ranged between radial and pure distention. The S1 direction oscillated around a vertical trend, while s3 was sub-horizontal, with a predominant N230-050° direction. Ar-Ar ages in biotite obtained from the extensional shear zones ranged from 480 and 490 Ma. Together, data obtained for the structures associated with the late extensional regimen described in the present study suggest that its nucleation is associated with distal and brittle-ductile sectors of the gravitational collapse zone of Araçuaí-West Congo Orogen.

scholarly journals The Borborema Strike-Slip Shear Zone System (NE Brazil): Large-Scale Intracontinental Strain Localization in a Heterogeneous Plate

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 6) ◽  
Author(s):  
Sergio P. Neves ◽  
Andréa Tommasi ◽  
Alain Vauchez ◽  
Thais Andressa Carrino
Keyword(s):  
Shear Zone ◽  
Large Scale ◽  
Shear Zones ◽  
Strike Slip ◽  
Northeastern Brazil ◽  
Main Stage ◽  
Plate Boundaries ◽  
Deformation Localization ◽  
Continental Scale ◽  
Dextral Shear

Abstract Large-scale strike-slip faults are fundamental tectonic elements of the continental lithosphere. They constitute plate boundaries (continental transforms), separate terranes with contrasting geological histories within accretionary orogens, or accommodate heterogeneous deformation in intracontinental settings. In ancient orogens, where deeper levels of the crust are exposed, these faults are expressed as shear zones materialized by up to tens of km-wide mylonitic belts. The Borborema shear zone system in northeastern Brazil is one of the largest and best-exposed intracontinental strike-slip shear zone systems in the world, cropping out over 250,000 km2. Here, we review its main geophysical, structural, petrologic, and geochronologic characteristics and discuss the factors controlling its development. This complex continental scale shear zone system is composed of a set of NE- to NNE-trending dextral shear zones from which there are two major E-trending dextral shear zones with horse-tail terminations into the transpressional belt branch, as well as several smaller E-trending dextral and NE-trending dextral and sinistral shear zones. The major shear zones are marked by extensive linear or curvilinear magnetic gradients, implying their continuation at depth. The major shear zones are materialized by migmatite to amphibolite-facies mylonites, but the entire system shows evidence of late deformation at lower temperatures. The system developed during the late stages of the Neoproterozoic Brasiliano (Pan-African) orogeny (mainly from 590 to 560 Ma), postdating by more than 20 Ma the main stage of contractional deformation. Localization of strike-slip shearing in this intraplate setting was controlled by rheological contrasts between blocks with distinct Paleoproterozoic histories, the presence of preorogenic Neoproterozoic rifts, the craton geometry, and zones of enhanced magmatic activity, highlighting the importance of rheological heterogeneity in controlling shear zone nucleation and evolution.

scholarly journals Kinematics and Geochronology of Late Paleozoic–Early Mesozoic Ductile Deformation in the Alxa Block, NW China: New Constraints on the Evolution of the Central Asian Orogenic Belt

Lithosphere ◽  
2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Beihang Zhang ◽  
Jin Zhang ◽  
Heng Zhao ◽  
Junfeng Qu ◽  
Yiping Zhang ◽  
...  
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Late Paleozoic ◽  
Ductile Shear Zone ◽  
Early Mesozoic ◽  
Central Asian ◽  
Ductile Shear Zones ◽  
Dextral Shear ◽  
Ductile Shear

Abstract Strike-slip faults are widely developed throughout the Central Asian Orogenic Belt (CAOB), one of the largest Phanerozoic accretionary orogenic collages in the world, and may have played a key role in its evolution. Recent studies have shown that a large number of Late Paleozoic–Early Mesozoic ductile shear zones developed along the southern CAOB. This study reports the discovery of a NW–SE striking, approximately 500 km long and up to 2 km wide regional ductile shear zone in the southern Alxa Block, the Southern Alxa Ductile Shear Zone (SADSZ), which is located in the central part of the southern CAOB. The nearly vertical mylonitic foliation and subhorizontal stretching lineation indicate that the SADSZ is a ductile strike-slip shear zone, and various kinematic indicators indicate dextral shearing. The zircon U-Pb ages and the 40Ar/39Ar plateau ages of the muscovite and biotite indicate that the dextral ductile shearing was active during Middle Permian to Middle Triassic (ca. 269–240 Ma). The least horizontal displacement of the SADSZ is constrained between ca. 40 and 50 km. The aeromagnetic data shows that the SADSZ is in structural continuity with the coeval shear zones in the central and northern Alxa Block, and these connected shear zones form a ductile strike-slip duplex in the central part of the southern CAOB. The ductile strike-slip duplex in the Alxa Block, including the SADSZ, connected the dextral ductile shear zones in the western and eastern parts of the southern CAOB to form a 3000 km long E-W trending dextral shear zone, which developed along the southern CAOB during Late Paleozoic to Early Mesozoic. This large-scale dextral shear zone was caused by the eastward migration of the orogenic collages and blocks of the CAOB and indicates a transition from convergence to transcurrent setting of the southern CAOB during Late Paleozoic to Early Mesozoic.

scholarly journals The Dabie Extensional Tectonic System: Structural Framework

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Quanlin Hou ◽  
Hongyuan Zhang ◽  
Qing Liu ◽  
Jun Li ◽  
Yudong Wu
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Ultrahigh Pressure ◽  
Metamorphic Complex ◽  
The South ◽  
Magma Intrusion ◽  
The North ◽  
Extensional Tectonic ◽  
Mechanism Transition ◽  
Tectonic System

A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56 km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12 km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190 Ma and ~124 Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later.

Effect of kinematics of orogenic wedge on kinematic evolutionary paths and deformation profiles of major shear zones: An example from the eastern Himalaya 

2021 ◽  
Author(s):  
Pritam Ghosh ◽  
Kathakali Bhattacharyya
Keyword(s):  
Shear Zone ◽  
Strain Softening ◽  
Leading Edge ◽  
Shear Zones ◽  
Deformation History ◽  
Progressive Deformation ◽  
Trailing Edge ◽  
Orogenic Wedge ◽  
Transport Direction ◽  
Evolutionary Paths

&lt;p&gt;We examine how the deformation profile and kinematic evolutionary paths of two major shear zones with prolonged deformation history and large translations differ with varying structural positions along its transport direction in an orogenic wedge. We conduct this analysis on multiple exposures of the internal thrusts from the Sikkim Himalayan fold thrust belt, the Pelling-Munsiari thrust (PT), the roof thrust of the Lesser Himalayan duplex (LHD), and the overlying Main Central thrust (MCT). These two thrusts are regionally folded due to growth of the LHD and are exposed at different structural positions. The hinterlandmost exposures of the MCT and PT zones lie in the trailing parts of the duplex, while the foreland-most exposures of the same studied shear zones lie in the leading part of the duplex, and thus have recorded a greater connectivity with the duplex. The thicknesses of the shear zones progressively decrease toward the leading edge indicating variation in deformation conditions. Thickness-displacement plot reveals strain-softening from all the five studied MCT and the PT mylonite zones. However, the strain-softening mechanisms varied along its transport direction with the hinterland exposures recording dominantly dislocation-creep, while dissolution-creep and reaction-softening are dominant in the forelandmost exposures. Based on overburden estimation, the loss of overburden on the MCT and the PT zones is more in the leading edge (~26km and ~15km, respectively) than in the trailing edge (~10km and ~17km, respectively), during progressive deformation. Based on recalibrated recrystallized quartz grain thermometer (Law, 2014), the estimated deformation temperatures in the trailing edge are higher (~450-650&amp;#176;C) than in the leading edge (350-550&amp;#176;C) of the shear zones. This variation in the deformation conditions is also reflected in the shallow-crustal deformation structures with higher fracture intensity and lower spacing in the leading edge exposures of the shear zones as compared to the trailing edge exposures.&lt;/p&gt;&lt;p&gt;The proportion of mylonitic domains and micaceous minerals within the exposed shear zones increase and grain-size of the constituent minerals decreases progressively along the transport direction. This is also consistent with progressive increase in mean R&lt;sub&gt;s&lt;/sub&gt;-values toward leading edge exposures of the same shear zones. Additionally, the &amp;#945;-value (stretch ratio) gradually increases toward the foreland-most exposures along with increasing angular shear strain. Vorticity estimates from multiple incremental strain markers indicate that the MCT and PT zones generally record a decelerating strain path. Therefore, the results from this study are counterintuitive to the general observation of a direct relationship between higher Rs-value and higher pure-shear component. We explain this observation in the context of the larger kinematics of the orogen, where the leading edge exposures have passed through the duplex structure, recording the greatest connectivity and most complete deformation history, resulting in the weakest shear zone that is also reflected in the deformation profiles and strain attributes. This study demonstrates that the same shear zone records varying deformation profile, strain and kinematic evolutionary paths due to varying deformation conditions and varying connectivity to the underlying footwall structures during progressive deformation of an orogenic wedge.&lt;/p&gt;

Comment on “Miocene to Quaternary tectonostratigraphic evolution of the middle section of the Burdur-Fethiye Shear Zone, south-western Turkey: Implications for the wide inter-plate shear zones. Tectonophysics 690, 336–354”

2018 ◽  
Vol 722 ◽  
pp. 595-600 ◽  
Author(s):  
M. Cihat Alçiçek ◽  
Lars W. van den Hoek Ostende ◽  
Gerçek Saraç ◽  
Alexey S. Tesakov ◽  
Alison M. Murray ◽  
...  
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Middle Section ◽  
Western Turkey

scholarly journals Petrogenesis and tectonic of the Urucum granitic suite, Rio Doce Valley (Minas Gerais - Brazil): an example of syn to late collisional peraluminous magmatism associated with high-angle transcurrent shear zone

2015 ◽  
Vol 45 (1) ◽  
pp. 127-141 ◽  
Author(s):  
Hermínio Arias Nalini Júnior ◽  
Rômulo Machado ◽  
Essaid Bilal
Keyword(s):  
Trace Elements ◽  
Solid State ◽  
Shear Zone ◽  
Saturation Index ◽  
Minas Gerais ◽  
High Angle ◽  
Accessory Minerals ◽  
Major Oxides ◽  
Minas Gerais State ◽  
Alumina Saturation Index

The Urucum suite (582 ± 2 Ma, zircon U-Pb age), situated in the Mid-Rio Doce Valley, eastern part of Minas Gerais State, is characterized by elongated, NW-SE and N-S trending granitic massifs associated with the Conselho Peña-Resplendor high-angle shear zone. It corresponds to a syn to late collisional magmatism that presents dominant solid-state foliation. Four facies are distinguished within the Urucum suite: (i) a porphyritic (Urucum); (ii) a medium- to coarse nequigranular (Palmital); (iii) a tourmaline-bearing; and (iv) a pegmatitic facies. These facies are peraluminous, with alumina saturation index varying from 0.98 to 1.38. SiO2 contents vary from 70.7 to 73.7 wt%, with K2O values ranging from 3.5 to 5.7 wt%, Na2O from 1.9 to 4.4 wt%, MgO from 0.6 to 1.2 wt%, and CaO from 0.3 to 0.9%. Harker-type diagrams show rather continuous trends from the less-evolved Urucum facies to the more evolved tourmaline-bearing and pegmatitic facies. The behavior of several major oxides and trace elements (Fe2O3, MgO, MnO, CaO, TiO2, Al2O3, K2O, Rb and Ba) reflects the role played by fractionation of ferromagnesian minerals, feldspars and accessory minerals. Initial Sr87/Sr86 ratios vary from 0.711 to 0.716, with εNd (580 Ma) values between -7.4 to -8.2, and Sm-Nd TDM model ages ranging from 2290 to 1840 Ma.

scholarly journals Origin of chromitites in the Esker Intrusive Complex, Ring of Fire Intrusive Suite, as revealed by chromite trace element chemistry and simple crystallization models

2021 ◽  
Author(s):  
J M Brenan ◽  
K Woods ◽  
J E Mungall ◽  
R Weston
Keyword(s):  
Partition Coefficients ◽  
Fluid Dynamic ◽  
Experimental Studies ◽  
Wall Rock ◽  
Major And Trace Elements ◽  
Iron Formation ◽  
Intrusive Complex ◽  
Banded Iron Formation ◽  
Magma Flow ◽  
Intrusive Suite

To better constrain the origin of the chromitites associated with the Esker Intrusive Complex (EIC) of the Ring of Fire Intrusive Suite (RoFIS), a total of 50 chromite-bearing samples from the Black Thor, Big Daddy, Blackbird, and Black Label chromite deposits have been analysed for major and trace elements. The samples represent three textural groups, as defined by the relative abundance of cumulate silicate phases and chromite. To provide deposit-specific partition coefficients for modeling, we also report on the results of laboratory experiments to measure olivine- and chromite-melt partitioning of V and Ga, which are two elements readily detectable in the chromites analysed. Comparison of the Cr/Cr+Al and Fe/Fe+Mg of the EIC chromites and compositions from previous experimental studies indicates overlap in Cr/Cr+Al between the natural samples and experiments done at &amp;gt;1400oC, but significant offset of the natural samples to higher Fe/Fe+Mg. This is interpreted to be the result of subsolidus Fe-Mg exchange between chromite and the silicate matrix. However, little change in Cr/Cr+Al from magmatic values, owing to the lack of an exchangeable reservoir for these elements. A comparison of the composition of the EIC chromites and a subset of samples from other tectonic settings reveals a strong similarity to chromites from the similarly-aged Munro Township komatiites. Partition coefficients for V and Ga are consistent with past results in that both elements are compatible in chromite (DV = 2-4; DGa ~ 3), and incompatible in olivine (DV = 0.01-0.14; DGa ~ 0.02), with values for V increasing with decreasing fO2. Simple fractional crystallization models that use these partition coefficients are developed that monitor the change in element behaviour based on the relative proportions of olivine to chromite in the crystallizing assemblage; from 'normal' cotectic proportions involving predominantly olivine, to chromite-only crystallization. Comparison of models to the natural chromite V-Ga array suggests that the overall positive correlation between these two elements is consistent with chromite formed from a Munro Township-like komatiitic magma crystallizing olivine and chromite in 'normal' cotectic proportions, with no evidence of the strong depletion in these elements expected for chromite-only crystallization. The V-Ga array can be explained if the initial magma responsible for chromite formation is slightly reduced with respect to the FMQ oxygen buffer (~FMQ- 0.5), and has assimilated up to ~20% of wall-rock banded iron formation or granodiorite. Despite the evidence for contamination, results indicate that the EIC chromitites crystallized from 'normal' cotectic proportions of olivine to chromite, and therefore no specific causative link is made between contamination and chromitite formation. Instead, the development of near- monomineralic chromite layers likely involves the preferential removal of olivine relative to chromite by physical segregation during magma flow. As suggested for some other chromitite-forming systems, the specific fluid dynamic regime during magma emplacement may therefore be responsible for crystal sorting and chromite accumulation.

Sign in / Sign up

Export Citation Format

Share Document