Geology of the Mesozoic Volcanic and Sedimentary Rocks East of Pemberton, British Columbia

Riddell, Janet

doi:10.4095/132519

Cited by 3 publications

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“…Farther south, Late Jurassic to Early Cretaceous amalgamation of terranes may be recorded by quartz-rich overlap strata. Late Juras-sic granitic boulders contained in these strata provide a maximum overlap age that "links" Wrangellia to Bridge River-Methow terranes (Friedman and Armstrong, 1995;Riddell, 1991). However, strata as young as Cenomanian (ca.…”

Section: Evidence For the Mezcalera-angayucham Suturementioning

confidence: 99%

Mantle and geological evidence for a Late Jurassic−Cretaceous suture spanning North America

Sigloch¹,

Mihalynuk²

2017

GSA Bulletin

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Crustal blocks accreted to North America form two major belts that are separated by a tract of collapsed Jurassic-Cretaceous basins extending from Alaska to Mexico. Evidence of oceanic lithosphere that once underlay these basins is rare at Earth's surface. Most of the lithosphere was subducted, which accounts for the general difficulty of reconstructing oceanic regions from surface evidence. However, this seafloor was not destroyed; it remains in the mantle beneath North America and is visible to seismic tomography, revealing configurations of arc-trench positions back to the breakup of Pangea. The double uncertainty of where trenches ran and how subducting lithosphere deformed while sinking in the mantle is surmountable, owing to the presence of a special-case slab geometry. Wall-like, linear slab belts exceeding 10,000 km in length appear to trace out intra-oceanic subduction zones that were stationary over tens of millions of years, and beneath which lithosphere sank almost vertically. This hypothesis sets up an absolute lower-mantle reference frame. Combined with a complete Atlantic spreading record that positions paleo-North America in this reference frame, the slab geometries permit detailed predictions of where and when ocean basins at the leading edge of westwarddrifting North America were subducted, how intra-oceanic subduction zones were overridden, and how their associated arcs and basement terranes were sutured to the continent. An unconventional paleogeography is predicted in which mid-to late Mesozoic arcs grew in a long-lived archipelago located 2000-4000 km west of Pangean North America (while also consistent with the conventional view of a continental arc in early Mesozoic times). The Farallon Ocean subducted beneath the outboard (western) edge of the archipelago, whereas North America converged on the archipelago by westward subduction of an intervening, major ocean, the Mezcalera-Angayucham Ocean. The most conspicuous geologic prediction is that of an oceanic suture that must run along the entire western margin of North America. It formed diachronously between ca. 155 Ma and ca. 50 Ma, analogous to diachro nous suturing of southwest Pacific arcs to the northward-migrating Australian continent today. We proceed to demonstrate that this suture prediction fits the spatio-temporal evidence for the collapse of at least 11 Middle Jurassic to Late Cretaceous basins wedged between the Intermontane and Insular-Guerrero superterranes, about half of which are known to contain mantle rocks. These relatively late suturing ages run counter to the Middle Jurassic or older timing required and asserted by the prevailing, Andean-analogue model for the North American Cordillera. We show that the arguments against late suturing are controvertible, and we present multiple lines of direct evidence for late suturing, consistent with geophysical observations. We refer to our close integration of surface and subsurface evidence from geology and geophysics as "tomotectonic analysis." This type of analysis provides a str...

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Section: Evidence For the Mezcalera-angayucham Suturementioning

confidence: 99%

Mantle and geological evidence for a Late Jurassic−Cretaceous suture spanning North America

Sigloch¹,

Mihalynuk²

2017

GSA Bulletin

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The Coast Belt Thrust System: Evidence of Late Cretaceous shortening in southwest British Columbia

Journeay¹,

Friedman²

1993

Tectonics

106

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The Coast Belt Thrust System (CBTS) is the leading edge of a west vergent contractional belt that formed along the inboard margin of the Insular superterrane in late Cretaceous time. The foreland of this contractional belt comprises a system of east dipping frontal thrusts that imbricate Jurassic and Early Cretaceous supracrustal arc sequences and related plutonic suites of the Westem Coast Belt (WCB). These faults root eastward into an imbricate zone of folded thrusts and out-of-sequence reverse faults across which the metamorphic gradient has been stmcturally inverted. To the east and stmcturally above the imbricate zone is a folded stack of high-pressure thrust sheets comprising metamorphosed island arc and oceanic rocks of the Central Coast Belt (CCB). These rocks represent the exhumed crustal root of the CBTS. Metamorphosed volcanic and volcaniclastic rocks that occur in thrust sheets of the imbricate zone yield U-Pb zircon dates which support a correlation with lower-plate Jurassic and Early Cretaceous arc sequences of the WCB. Structural and geochronologic data indicate a two-stage history of Late Cretaceous shortening. During the early stage of shortening, supracrustal arc and related basin sequences along the inboard margin of the Insular superterrane were stmcturally imbricated and accreted to the toe (footwall) of a westward prograding accretionary complex made up of previously assembled terranes of the CCB. These early-stage structures are represented by folded thrusts in the imbricate and hinterland zones of the CBTS. The timing of this earlystage thrusting is bracketed by the emplacement of synorogenic plutonic suites, which yield U-Pb zircon dates of 97 + 1 Ma and 96 +6/-3 Ma. Late-stage shortening involved both thin-skinned thrusting and folding of Jura-Cretaceous arc sequences in the WCB foreland and out-ofsequence thrusting of higher-grade thrust sheets in the imbricate and hinterland zones of the CBTS. In the foreland this episode of deformation is bracketed by late-and postkinematic plutons, which yield U-Pb zircon dates of 94 + 2 Ma and 91 +4/-3 Ma, respectively. In the imbricate zone, this episode of deformation is bracketed by the emplacement of synkinemafic and postkinematic plutons, which yield U-Pb zircon dates of 96 +6/-3 Ma and 94 +6/-5 Ma, respectively. The development of thick-skinned out-of-Copyfight 1993 by the American Geophysical Union. Paper number 92TC02773. 0278-7407/93/92TC-02773510.00 sequence thrusts in the imbricate and hinterland zones of the CBTS signals a northeastward migration of the deformation front in Late Cretaceous time. This shift in the locus of thrusting resulted in southwestward telescoping and structural inversion of the metamorphic hinterland and may account for the complex stacking order and thermal history of the Southern Coast Belt. INTRODUCTION The Coast Belt of southern British Columbia straddles the boundary between the Insular and Intermontane superterranes (Figure 1). It comprises an array of faultbounded island arc and oceanic terranes that were ac...

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Mid‐Cretaceous thrusting in the southern Coast Belt, British Columbia and Washington, after strike‐slip fault reconstruction

Umhoefer¹,

Miller²

1996

Tectonics

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A major thrust system of mid-Cretaceous age is present along much of the Coast Belt of northwestern. North America. Thrusting was concurrent, and spatially coincided, with emplacement of a great volume of arc intrusives and minor local strike-slip faulting. In the southern Coast Belt (52 ø to 47øN), thrusting was followed by major dextral-slip faulting, which resulted in significant translational shuffling of the thrust system. In this paper, we restore the displacements on major dextral-slip faults of the southern Coast Belt and then analyze the mid-Cretaceous thrust system. Two reconstructions were made that use dextral faulting on the Yalakom fault (115 km), Castle Pass and Ross Lake faults (10 km), and Fraser fault (100 km). The reconstructions differ in the amount of dextral offset on the Straight Creek fault (160 and 100 km) and how much the NE part of the Cascades crystalline core expanded (30 km and 0 km) during Eocene extension. Reconstruction A produces the best match of lithotectonic units and thrust systems. Our synthesis shows that the southern Coast Belt thrust system was >250 -180 km wide after thrusting. The thrust system was mainly southwest vergent but had a belt of northeast vergent back thrusts on the northeast side associated with the Tyaughton-Methow basin, which may indicate large-scale tectonic wedging. Thrust faults are commonly low to moderate angle, but high angle faults also occur, especially as late stage, out-of-sequence, structures involving plutons. The amount of thrust displacement across the system is unknown but must be at least 100 km and may be many hundreds of kilometers. Most thrusting occurred from -100 to -80 Ma and did not migrate systematically until after-90 Ma, when thrusting and magmatism shifted to the northeast for a few million years. Widespread thrusting occurred both near plutons and where there are no (or small) plutons, which strongly suggests that thrust faulting was caused by regional-to plate-scale forces such as rapid plate convergence and/or arc-continent collision. The mid-Cretaceous thrust system in the southern Coast Belt is the focus of this paper. This deformation episode (~ 100 -80 Ma) is the major tectonic event in the belt, during which there was voluminous magmatism and metamorphism and basins subsided and were inverted. Deformation continued after ~80 Ma, but it changed significantly to a narrower belt dominated by strike-slip and thrust faulting and less voluminous magmatism. Thus the southern Coast Belt is a prime example of a complex, synmagmatic thrust belt that was overprinted by major strike-slip faults. The cause of the mid-Cretaceous contraction in the Coast Belt is controversial. In one hypothesis, the final accretion of the Insular superterrane involved an oceanic arc-continental arc collision that caused regional contraction as the outer plate (Insular terrane) continued to subduct and collide with North America [Monger et al., 1982; Thorkelson and Smith, 1989]. In a second model, the regional contraction results from the telescoping o...

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Geology of the Mesozoic Volcanic and Sedimentary Rocks East of Pemberton, British Columbia

Cited by 3 publications

References 0 publications

Mantle and geological evidence for a Late Jurassic−Cretaceous suture spanning North America

Mantle and geological evidence for a Late Jurassic−Cretaceous suture spanning North America

The Coast Belt Thrust System: Evidence of Late Cretaceous shortening in southwest British Columbia

Mid‐Cretaceous thrusting in the southern Coast Belt, British Columbia and Washington, after strike‐slip fault reconstruction

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