Extracting ore-deposit-controlling structures from aeromagnetic, gravimetric, topographic, and regional geologic data in western Yukon and eastern Alaska

2014 ◽  
Vol 2 (4) ◽  
pp. SJ75-SJ102 ◽  
Author(s):  
Matías G. Sánchez ◽  
Murray M. Allan ◽  
Craig J. R. Hart ◽  
James K. Mortensen
Keyword(s):  
Late Cretaceous ◽  
Spatial Density ◽  
Variable Intensity ◽  
North American Cordillera ◽  
Magmatic Arc ◽  
Fault Systems ◽  
The North ◽  
Dextral Strike Slip Fault ◽  
Geologic Maps ◽  
First Vertical Derivative

Aeromagnetic lineaments interpreted from reduced-to-pole (RTP) magnetic grids were compared with gravity, topography, and field-based geologic maps to infer regional structural controls on hydrothermal mineral occurrences in a poorly exposed portion of the North American Cordillera in western Yukon and eastern Alaska. High-frequency and variable-intensity aeromagnetic lineaments corresponding to discontinuities with an aeromagnetic domain change were interpreted as steep-dipping and either magnetite-destructive or magnetite-additive faults. These structures were interpreted to be predominantly Cretaceous in age and to have formed after the collision of the Intermontane terranes with the ancient Pacific margin of North America. To demonstrate the reliability of the aeromagnetic interpretation, we developed a multidata set stacking methodology that assigns numeric values to individual lineaments depending on whether they can be traced in residuals and first vertical derivative of RTP aeromagnetic grids, isostatic residual gravity grids, digital topography, and regional geologic maps. The sum of all numeric values was used to estimate the likelihood of the aeromagnetic lineament as a true geologic fault. Fault systems were interpreted from zones of lineaments with high spatial density. Using this procedure, 10 major northwest-trending fault systems were recognized. These were oriented subparallel to the regional Cordilleran deformation fabric, the mid-Cretaceous Dawson Range magmatic arc, and well-established crustal-scale dextral strike-slip fault systems in the area. These orogen-parallel fault systems were interpreted to play a structural role in the emplacement of known porphyry Cu-Au and epithermal Au systems of mid-Cretaceous (115–98 Ma) and Late Cretaceous (79–72 Ma) age. The procedure also identified seven northeast-trending, orogen-perpendicular fault-fracture systems that are prominent in eastern Alaska and exhibit sinistral-to-oblique extensional kinematics. These structures were interpreted to govern the emplacement of Late Cretaceous (72–67 Ma) porphyry Mo- and Ag-rich polymetallic vein and carbonate replacement systems in the region.

LATE CRETACEOUS EXHUMATION OF UNDERPLATED METASEDIMENTARY ROCKS IN THE NORTH AMERICAN CORDILLERA

2019 ◽  
Author(s):  
William A. Matthews ◽  
◽  
Marie-Pier Boivin ◽  
Kirsten Sauer ◽  
Daniel S. Coutts
Keyword(s):  
Late Cretaceous ◽  
North American ◽  
North American Cordillera ◽  
Metasedimentary Rocks ◽  
The North

Oceanic crust generation in an island arc tectonic setting, SE Anatolian orogenic belt (Turkey)

2004 ◽  
Vol 141 (5) ◽  
pp. 583-603 ◽  
Author(s):  
OSMAN PARLAK ◽  
VOLKER HÖCK ◽  
HÜSEYİN KOZLU ◽  
MICHEL DELALOYE
Keyword(s):  
Late Cretaceous ◽  
Subduction Zones ◽  
Wide Spectrum ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Orogenic Belt ◽  
Mature Stage ◽  
Magmatic Arc ◽  
The North ◽  
Suprasubduction Zone

A number of Late Cretaceous ophiolitic bodies are located between the metamorphic massifs of the southeast Anatolian orogenic system. One of them, the Göksun ophiolite (northern Kahramanmaraş), which crops out in a tectonic window bounded by the Malatya metamorphic units on both the north and south, is located in the EW-trending nappe zone of the southeast Anatolian orogenic belt between Göksun and Afşin (northern Kahramanmaraş). It consists of ultramafic–mafic cumulates, isotropic gabbro, a sheeted dyke complex, plagiogranite, volcanic rocks and associated volcanosedimentary units. The ophiolitic rocks and the tectonically overlying Malatya–Keban metamorphic units were intruded by syn-collisional granitoids (∼ 85 Ma). The volcanic units are characterized by a wide spectrum of rocks ranging in composition from basalt to rhyolite. The sheeted dykes consist of diabase and microdiorite, whereas the isotropic gabbros consist of gabbro, diorite and quartzdiorite. The magmatic rocks in the Göksun ophiolite are part of a co-magmatic differentiated series of subalkaline tholeiites. Selective enrichment of some LIL elements (Rb, Ba, K, Sr and Th) and depletion of the HFS elements (Nb, Ta, Ti, Zr) relative to N-MORB are the main features of the upper crustal rocks. The presence of negative anomalies for Ta, Nb, Ti, the ratios of selected trace elements (Nb/Th, Th/Yb, Ta/Yb) and normalized REE patterns all are indicative of a subduction-related environment. All the geochemical evidence both from the volcanic rocks and the deeper levels (sheeted dykes and isotropic gabbro) show that the Göksun ophiolite formed during the mature stage of a suprasubduction zone (SSZ) tectonic setting in the southern branch of the Neotethyan ocean between the Malatya–Keban platform to the north and the Arabian platform to the south during Late Cretaceous times. Geological, geochronological and petrological data on the Göksun ophiolite and the Baskil magmatic arc suggest that there were two subduction zones, the first one dipping beneath the Malatya–Keban platform, generating the Baskil magmatic arc and the second one further south within the ocean basin, generating the Göksun ophiolite in a suprasubduction zone environment.

scholarly journals Tectonic setting of Cretaceous porphyry copper deposits of northern Chile (28°-30° S) and its relations with magmatic evolution and metallogeny

2020 ◽  
Vol 47 (3) ◽  
pp. 469
Author(s):  
Christian Creixell ◽  
Javier Fuentes ◽  
Hessel Bierma ◽  
Esteban Salazar
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Porphyry Copper ◽  
Northern Chile ◽  
Porphyry Copper Deposits ◽  
The West ◽  
Copper Deposits ◽  
Magmatic Arc ◽  
Fault Systems ◽  
Back Arc

Cretaceous porphyry copper deposits of northern Chile (28º-29º30’ S) are genetically related with dacitic to dioritic porphyries and they represent a still poorly-explored target for Cu resources. The porphyries correspond to stocks distributed into two separated discontinuous NS trending belts of different age. The location of these porphyries is generally adjacent to orogen-parallel major fault systems that extend along the studied segment and also have a marked temporal relationship with deformation events registered along these structures. A first episode of Cu-bearing porphyry emplacement took place between 116 and 104 Ma (Mina Unión or Frontera, Cachiyuyo, Punta Colorada, Dos Amigos, Tricolor porphyries). These Early Cretaceous dacite to diorite porphyries are spatially associated with the eastern segments of the Atacama Fault System, which records sinistral transpression that started at 121 Ma producing ground uplift, consequent denudation and exhumation of the Early Cretaceous magmatic arc. This resulted in a change from marine to continental deposition with an angular unconformity in the site of the back-arc basin after of eastward migration of the deformation around 112-110 Ma. At the scale of the continental margin, this deformation is correlated with early stage of the Mochica Orogenic event described in Perú. A second episode of Cu-bearing porphyry emplacement occurred between 92 and 87 Ma (Elisa, Johana, Las Campanas and La Verde deposits), which are spatially and temporally associated with the regional-scale Las Cañas-El Torito reverse fault, active between 89 and 84 Ma, during the Peruvian Orogenic Phase. This fault up thrust to the west part of the Chañarcillo Group rocks (Lower Cretaceous) over the younger upper levels of the Cerrillos Formation (Upper Cretaceous). The integrated geological mapping and geochemical data of the Early to Late Cretaceous volcanic rocks indicates that both Early Cretaceous sinistral transpression and Late Cretaceous east-west compression were not significant in promote changes in magma genesis, except for slight changes in trace element ratios (increase in Th/Ta, Nb/Ta and La/Yb) suggesting that the Late Cretaceous deformation event produced only slightly increase in crustal thickness (>40 km), but far from being comparable to major Cenozoic orogenic phases, at least along the magmatic arc to back-arc domains in the study area. Finally, our study give insights about regional geological parameters that can be used as a first order guide for exploration of Cu resources along Cretaceous magmatic belts of northern Chile, where both Early and Late Cretaceous Cu-bearing porphyry intrusions are restricted to a large structural block bounded to the west and east by Cretaceous fault systems.

The mid-Cretaceous Peninsular Ranges orogeny: a new slant on Cordilleran tectonics? II: northern United States and Canada

2021 ◽  
Author(s):  
Robert S. Hildebrand ◽  
Joseph B. Whalen
Keyword(s):  
United States ◽  
High Grade ◽  
North American Cordillera ◽  
Magmatic Arc ◽  
The North ◽  
Peninsular Ranges ◽  
Northern United States ◽  
Back Arc ◽  
Cordilleran Tectonics ◽  
Washington Cascades

The mid-Cretaceous Peninsular Ranges orogeny occurred in the North American Cordillera and affected rocks from Mexico to Alaska. It formed when a marine trough, open for ~35 Myr, closed by westerly subduction beneath a 140-100 Ma arc complex. In Part I we described the features of the orogen in Mexico and California, west to east: back-arc trough, magmatic arc, 140-100 Ma seaway, post-collisional 99-84 Ma granodioritic-tonalitic plutons emplaced into the orogenic hinterland during exhumation, an east-vergent thrust belt, and farther east, a flexural foredeep. In western Nevada, where the Luning–Fencemaker thrust might be a mid-Cretaceous feature, arc and post-collisional plutons occur in proximity. The orogen continues through the Helena salient and Washington Cascades. In British Columbia, rocks of the 130-100 Ma Gambier arc lie west of the exhumed orogenic hinterland and 99-84 Ma post-collisional plutons to collectively indicate westerly subduction. East-dipping reverse faults near Harrison Lake, active from ~100 Ma until ~90 Ma, shed 99-84 Ma debris westward into the Nanaimo back-arc region. Within Insular Alaska, the Early Cretaceous Gravina basinal arc assemblage was deformed at 100 Ma, and flanked to the east by a high-grade hinterland cut by post-collisional plutons. In mainland Alaska, the 100 Ma collision of Wrangellia and the Yukon-Tanana-Farewell composite terrane occurred above a southward-dipping subduction zone as shown by the 130-100 Ma Chisana arc sitting on Wrangellia and southward-dipping, northerly vergent thrusts in the Lower Cretaceous Kahiltna basin to the north. The outboard back-arc region was filled with post-collisional detritus of the McHugh complex.

scholarly journals Detrital zircon geochronology along a structural transect across the Kahiltna assemblage in the western Alaska Range: Implications for emplacement of the Alexander-Wrangellia-Peninsular terrane against North America

Geosphere ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1774-1808 ◽  
Author(s):  
Stephen E. Box ◽  
Susan M. Karl ◽  
James V. Jones ◽  
Dwight C. Bradley ◽  
Peter J. Haeussler ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Detrital Zircon ◽  
Upper Jurassic ◽  
Island Arc ◽  
Igneous Rocks ◽  
Japan Trench ◽  
Alaska Range ◽  
Magmatic Arc ◽  
The North ◽  
Modern Analogue

Abstract The Kahiltna assemblage in the western Alaska Range consists of deformed Upper Jurassic and Cretaceous clastic strata that lie between the Alexander-Wrangellia-Peninsular terrane to the south and the Farewell and other pericratonic terranes to the north. Differences in detrital zircon populations and sandstone petrography allow geographic separation of the strata into two different successions, each consisting of multiple units, or petrofacies, with distinct provenance and lithologic characteristics. The northwestern succession was largely derived from older, inboard pericratonic terranes and correlates along strike to the southwest with the Kuskokwim Group. The southeastern succession is characterized by volcanic and plutonic rock detritus derived from Late Jurassic igneous rocks of the Alexander-Wrangellia-Peninsular terrane and mid- to Late Cretaceous arc-related igneous rocks and is part of a longer belt to the southwest and northeast, here named the Koksetna-Clearwater belt. The two successions remained separate depositional systems until the Late Cretaceous, when the northwestern succession overlapped the southeastern succession at ca. 81 Ma. They were deformed together ca. 80 Ma by southeast-verging fold-and-thrust–style deformation interpreted to represent final accretion of the Alexander-Wrangellia-Peninsular terrane along the southern Alaska margin. We interpret the tectonic evolution of the Kahiltna successions as a progression from forearc sedimentation and accretion in a south-facing continental magmatic arc to arrival and partial underthrusting of the back-arc flank of an active, south-facing island-arc system (Alexander-Wrangellia-Peninsular terrane). A modern analogue is the ongoing collision and partial underthrusting of the Izu-Bonin-Marianas island arc beneath the Japan Trench–Nankai Trough on the east side of central Japan.

scholarly journals Magmatism, migrating topography, and the transition from Sevier shortening to Basin and Range extension, western United States

2022 ◽  
Author(s):  
Jens-Erik Lund Snee ◽  
Elizabeth L. Miller
Keyword(s):  
Great Basin ◽  
Late Cretaceous ◽  
Basin And Range ◽  
Range Extension ◽  
Crustal Thickening ◽  
Data Sets ◽  
Geologic Mapping ◽  
North American Cordillera ◽  
The North ◽  
Volcanic Tableland

ABSTRACT The paleogeographic evolution of the western U.S. Great Basin from the Late Cretaceous to the Cenozoic is critical to understanding how the North American Cordillera at this latitude transitioned from Mesozoic shortening to Cenozoic extension. According to a widely applied model, Cenozoic extension was driven by collapse of elevated crust supported by crustal thicknesses that were potentially double the present ~30–35 km. This model is difficult to reconcile with more recent estimates of moderate regional extension (≤50%) and the discovery that most high-angle, Basin and Range faults slipped rapidly ca. 17 Ma, tens of millions of years after crustal thickening occurred. Here, we integrated new and existing geochronology and geologic mapping in the Elko area of northeast Nevada, one of the few places in the Great Basin with substantial exposures of Paleogene strata. We improved the age control for strata that have been targeted for studies of regional paleoelevation and paleoclimate across this critical time span. In addition, a regional compilation of the ages of material within a network of middle Cenozoic paleodrainages that developed across the Great Basin shows that the age of basal paleovalley fill decreases southward roughly synchronous with voluminous ignimbrite flareup volcanism that swept south across the region ca. 45–20 Ma. Integrating these data sets with the regional record of faulting, sedimentation, erosion, and magmatism, we suggest that volcanism was accompanied by an elevation increase that disrupted drainage systems and shifted the continental divide east into central Nevada from its Late Cretaceous location along the Sierra Nevada arc. The north-south Eocene–Oligocene drainage divide defined by mapping of paleovalleys may thus have evolved as a dynamic feature that propagated southward with magmatism. Despite some local faulting, the northern Great Basin became a vast, elevated volcanic tableland that persisted until dissection by Basin and Range faulting that began ca. 21–17 Ma. Based on this more detailed geologic framework, it is unlikely that Basin and Range extension was driven by Cretaceous crustal overthickening; rather, preexisting crustal structure was just one of several factors that that led to Basin and Range faulting after ca. 17 Ma—in addition to thermal weakening of the crust associated with Cenozoic magmatism, thermally supported elevation, and changing boundary conditions. Because these causal factors evolved long after crustal thickening ended, during final removal and fragmentation of the shallowly subducting Farallon slab, they are compatible with normal-thickness (~45–50 km) crust beneath the Great Basin prior to extension and do not require development of a strongly elevated, Altiplano-like region during Mesozoic shortening.

Tectono-stratigraphic terranes and mineral resource distributions in Mexico

1983 ◽  
Vol 20 (6) ◽  
pp. 1040-1051 ◽  
Author(s):  
Maria Fernanda Campa ◽  
Peter J. Coney
Keyword(s):  
North American ◽  
Late Paleozoic ◽  
North American Cordillera ◽  
Magmatic Arc ◽  
The North ◽  
Resource Distributions ◽  
Gold Silver ◽  
Lead Zinc ◽  
New Vision ◽  
The Republic

About 80% of the southern part of the North American Cordillera within the Republic of Mexico is made up of suspect terranes. These terranes are suspect because their paleogeographic setting with respect to cratonic North America at various times through much of Phanerozoic time is uncertain. Much of northeastern and southeastern Mexico is underlain by basement accreted during late Paleozoic time, an extension of the Appalachian–Ouachita orogeny. This orogen has been considerably modified by Jurassic strike-slip translations related to the opening of the Gulf of Mexico. Western and southwestern Mexico is largely made up of several distinct but coeval latest Jurassic to Late Cretaceous submarine magmatic arc terranes with unknown basement that appear to have accreted against the disrupted North American margin by early Tertiary time. Only northeastern Sonora and the State of Chihuahua appear to be floored by unmoved North American cratonic basement. The combined effect of Mesozoic accretions and translations essentially eliminates the overlap of South America upon Mexico that is drived from late Paleozoic – early Mesozoic reconstructions of the closed Atlantic Ocean. This new vision of accretionary and translational tectonics in Mexico has profound implications for the study of tectogenesis in the southern Cordillera as well as for the interpretation of Mexico's vast natural resources. Preliminary analysis indicates that Mexico's gold–silver and lead–zinc deposits are directly or indirectly related to the terrane distributions discussed.

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