Robert B. Miller

San Jose State University | SJSU

The interaction between subduction zones and oceanic spreading centers is a common tectonic process, and yet our understanding of how it is manifested in the geologic record is limited to a few well-constrained modern and ancient examples. In the Paleogene, at least one oceanic spreading center interacted with the northwestern margin of North Ameri...

Broad overlap between deformation and magmatism in active margins has spurred the development of a conceptual framework of direct tectonomagmatic links in both active and ancient arcs. Although widespread and highly influential, such models have only rarely been critically evaluated. Rigorously linking tectonism, geodynamics, lithospheric evolution...

The northern Cascade Mountains in Washington (USA) preserve an exceptional shallow to mid-crustal record of Eocene transtension marked by dextral strike-slip faulting, intrusion of dike swarms and plutons, rapid non-marine sedimentation, and ductile flow and rapid cooling in parts of the North Cascades crystalline core. Transtension occurred during...

The rheology and composition of arc crust and the overall evolution of continental magmatic arcs can be affected by sediment incorporation events. The exhumed Cretaceous–Eocene North Cascades arc exposes abundant metasedimentary rocks that were incorporated into the arc during multiple events. This study uses field relationships, detrital zircon ge...

Strike-slip faults form in a wide variety of tectonic settings and are a first-order control on the geometry and sediment accumulation patterns in adjacent sedimentary basins. Although the structural and depositional architecture of strike-slip basins is well documented, few studies of strike-slip basins have integrated depositional age, lithofacie...

Despite playing a fundamental role in all models of Himalayan tectonics, minimal data constraining the structural evolution, metamorphic history, and offset magnitude of the South Tibetan detachment system (STDS) are available. Here, we integrate petrofabric, finite strain, and kinematic data with metamorphic and deformation temperatures to generat...

Metasedimentary rocks in the mid- to lower crust of exhumed continental arcs preserve information about both sedimentary provenance and metamorphic pressure-temperature paths, providing a unique perspective on the tectonic history of an arc, including margin-parallel translation and sediment-burial mechanisms. The Swakane Biotite Gneiss (Washington...

Heavy rare earth element (HREE)-depleted trace-element patterns are a relatively common feature of granitoids within mature Cordilleran continental margin arcs (e.g., Sierra Nevada batholith, Coast Mountains batholith, North Cascades, Peninsular Ranges batholith). This depletion is commonly interpreted to indicate the presence of garnet during gran...

Deep plutonic systems represent an important link between lowercrustal melt-generation sites and higher-level regions of magma accumulation, but models for these systems are limited by the relative scarcity of exposed weakly deformed, deep-crustal plutons. Exceptions include the ca. 92.3-89.7 Ma, dominantly tonalitic Tenpeak pluton and the smaller,...

The Swakane Gneiss, interpreted to represent sedimentary strata metamorphosed at 8-12 kbar, is the deepest exposed crustal levels within the exhumed North Cascades continental magmatic arc, yet the nature and age of its protolith and the mechanism by which it was transported to deep-crustal levels remains unclear. Zircons from 11 paragneiss and sch...

The metasupracrustal units within the north-central Chelan block of the North Cascades Range, Washington are investigated to determine mechanisms and timescales of supracrustal rock incorporation into the deep crust of continental magmatic arcs. Zircon U-Pb and Hfisotope analyses were used to characterize the protoliths of metasedimentary and metai...

Detrital zircon U-Pb and Hf-isotope results from the Skagit Gneiss and Swakane Gneiss

The U-Pb age and Hf-isotope composition of detrital zircons from Jurassic to Upper Cretaceous sedimentary rocks adjacent to the southern North Cascades–Coast Plutonic Complex continental magmatic arc document shifting provenance, the tectonic evolution of the arc system, and translation along the continental margin. Systematic changes in the detrit...

Sheeted intrusive complexes represent unequivocal examples of incremental intrusive activity in plutonic systems and thus provide an opportunity to constrain processes associated with incremental magma emplacement. We present field observations, U-Pb zircon data, and whole-rock and mineral chemistry from the sheeted intrusive complex of the ca. 92...

The U-Pb and Hf isotope composition of detrital zircons from the Swakane Gneiss (SG) of the North Cascades, Washington and the Pelona-Orocopia-Rand schists (POR) of the southern California and southwestern Arizona are investigated to compare mechanisms of sediment incorporation into arc systems and to evaluate paleogeographic reconstructions. The S...

Studies of plutons indicate that they are the result of a complex interplay of magmatic processes occurring during magma generation, ascent, and emplacement. A critical tool for deciphering these processes is high-precision geochronology, which can help determine the timing and rates of magmatism in the crust. We conducted a field and U-Pb geochron...

The North Cascades orogen (northwestern USA) provides an exceptional natural laboratory with which to evaluate potential temporal and kinematic links between processes operating at a wide range of crustal levels during collapse of a continental arc, and particularly the compatibility of strain between the upper and lower crust. This magmatic arc re...

The rates at which large volumes of eruptible, silicic (> 65 wt% SiO2) magma (magma chambers) are assembled, as well as their longevity in the upper crust, remain controversial. This controversy is due, in part, to a missing record of granitoid plutonic complexes that represent large fossil upper crustal magma chambers. We present new geologic mapp...

The North Cascades is an excellent area to study basins and strike-slip faults that formed during regional Eocene transtension. This study focuses on the southern flank of the Cascades crystalline core where the Eocene Leavenworth fault zone (LFZ) separates Eocene non-marine clastic rocks of the Chumstick Formation to the east, from the older Swauk...

The Early Eocene Swauk Formation was deposited in a complex forearc setting during a regional shift from transpression to transtension associated with subduction of a spreading ridge beneath western North America. The basin forming mechanism for the Swauk Fm is not well understood; previous workers have suggested that it was a strike-slip basin, mo...

The North Cascades crystalline core is an ideal natural laboratory to study processes associated with deep burial and rapid exhumation of clastic sediments in magmatic arcs. The Swakane Biotite Gneiss (SBG), the youngest and structurally deepest meta-supracrustal unit in the Cascades core, was metamorphosed at 8-12 kb between ~73-68 Ma. Detrital zi...

The presence of early Eocene neartrench magmatism in western Washington and southern British Columbia has led to speculation that this area experienced ridge-trench interaction during that time. However, the effects of this process as they are preserved in other parts of the geologic record are poorly known. We present highprecision U-Pb zircon geo...

Detailed mapping of the geology of the Benson Lake pendant and surrounding intrusions is presented in a geologic map at 1:10,000 scale. Protoliths of the multiply deformed metasedimentary rocks of the pendant are Precambrian to Paleozoic shallow water passive margin deposits. The pendant is located between the 102 Ma intrusion of the Yosemite Valle...

Deep plutonic systems are commonly viewed as magma transfer zones and thus represent a critical link between deeper-crustal melt-generation sites and higher-level regions of magma accumulation. Models for deep-crustal plutonism are limited by the relative scarcity of exposures of deep crust and commonly strong metamorphic and structural overprintin...

Deep-crustal plutons are important for understanding heat, melting and mass transfer processes in the lower crust. Our comprehension of these processes influences perspectives of crustal growth and how magma ascends to form large volume batholiths in the upper crust. Despite the importance of these systems, it is difficult to study deep-crustal plu...

Incrementally constructed magma systems have been recognized from studies of the resulting plutons for more than three decades. However, magma addition rates, fluxes, growth durations, sizes of increments, and sizes and durations of the resulting magma chambers have been difficult to ascertain, emphasizing the need for a better understanding of how...

The Twisp Valley Schist (TVS) is important for both the correlation of terranes in the Cascades crystalline core and for the determination of the metamorphic pressure–temperature–time history of the northeastern part of the core. The TVS is a chaotically mixed unit of mainly siliceous schist (metachert) with significant amounts of metabasite, calc-...

The 93–96 Ma Mount Stuart batholith intruded across the boundary between the Northwest Cascades thrust system and the crystalline core of the North Cascades. Although previously considered posttectonic, the northeast margin of the Mount Stuart batholith and its wall rocks have been involved in syn- to post-emplacement, southwest-directed thrusting...

A steep mantle shear zone that deforms ultramafic rocks of the Jurassic Ingalls ophiolite is inferred to preserve a record of the interplay of melt impregnation, strain localization, and switching deformation mechanisms in a fossil oceanic fracture zone. This ~2-km-wide, E-W-striking shear zone separates harzburgite and dunite on the south from lhe...

The record of metamorphism, deformation, and melting in the North Cascades continental arc provides insights into the timing and mechanisms of extensional unroofing that followed crustal thickening. The Skagit Gneiss (North Cascades) is composed of variably deformed 90-45 Ma tonalitic to granitic intrusive rocks. These lithologies and metasedimenta...

The Sierra Nevada batholith is dominated by large, variably zoned, intrusive complexes, whose origins remain enigmatic and controversial despite decades of study. As exemplified by recent studies in the Tuolumne Intrusive Suite, knowing the petrogenetic processes responsible for zonation, the volumes of intrusive pulses, and the degree to which seq...

This volume contains guides for 33 geological field trips offered in conjunction with the October 2009 GSA Annual Meeting in Portland, Oregon. Showcasing the region’s geological diversity, the peer-reviewed papers included here span topics ranging from accreted terrains and mantle plumes to volcanoes, floods, and vineyard terroir. Locations visited...

Continental crust is displaced in strike-slip fault zones through lateral and vertical movement that together drive burial and exhumation. Pressure–temperature–deformation (P–T–d) histories of orogenic crust exhumed in transcurrent zones record the mechanisms and conditions of these processes. The Skagit Gneiss Complex, a migmatitic unit of the Nor...

The Tonga Formation, on the westernmost boundary of the Cascades crystalline core, records Cretaceous plutonism, contact to regional metamorphism, and multiple episodes of folding related to intense east-west contractional deformation. The Tonga Formation is exposed in a fault-bounded, north-south elongate tectonic domain that comprises pelite-psam...

The crystalline core of the North Cascades preserves a Cretaceous crustal section that facilitates evaluation of pluton construction, emplacement, geometry, composition, and deformation at widely variable crustal levels (~5 to 40 km paleodepth) in a thick (> 55 km) continental magmatic arc. The oldest and largest pulse of plutonism was focused betw...

Magmatic fabrics in plutons are often interpreted as records of magma flow rather than as records of regional strain in arcs. However, our field studies in the Sierra Nevada, California and elsewhere in Cordilleran arcs, provide examples of the benefits of studying plutons to constrain short increments of regional strain histories and inferred pale...

[Glazner and Bartley (2006)][1] suggest that stoping is an insignificant to potentially nonexistent process in the emplacement and evolution of magmatic systems. We strongly disagree with this conclusion and present here a number of alternative perspectives, which we group into three categories:

The Ingalls ophiolite complex, central Cascades, Washington, mainly consists of mantle-derived ultramafi c tectonite, with crustal rocks consisting of gabbro, diabase, basalt, and sedimentary rocks. The crustal rocks occur as faulted blocks within ser-pentinite mélange (Navaho Divide fault zone). Mafi c rocks in most of these blocks comprise the La...

The polygenetic Ingalls ophiolite complex in the central Cascades, Washington, is one of several Middle to Late Jurassic ophiolites of the North American Cordillera. It consists primarily of mantle tectonites. High-temperature mylonitic peridotite, over-printed by serpentinite mélange (Navaho Divide fault zone), separates harzburgite and dunite in...

The crystalline core of the North Cascades arc records the Cretaceous to Paleogene history of magmatism, deformation, and crustal growth along a segment of the North American Cordillera. The Nd isotopic compositions of granitoid plutons that intrude the Cascades core are a product of their source regions, and they provide probes of the crustal arch...