Exhumation across the Indus Suture Zone: a record of back sliding of the hanging wall

Terrane accretion forms lithospheric-scale fault systems that commonly experience long and complex slip histories. Unraveling the evolution of these suture zone fault systems yields valuable information regarding the relative importance of various upper crustal structures and their linkage through the lithosphere. We present new bedrock geologic mapping and geochronology data documenting the geologic evolution of reactivated shortening structures and adjacent metamorphic rocks in the Alaska Range suture zone at the inboard margin of the Wrangellia composite terrane in the eastern Alaska Range, Alaska, USA. Detrital zircon uranium-lead (U-Pb) age spectra from metamorphic rocks in our study area reveal two distinct metasedimentary belts. The Maclaren schist occupies the inboard (northern) belt, which was derived from terranes along the western margin of North America during the mid- to Late Cretaceous. In contrast, the Clearwater metasediments occupy the outboard (southern) belt, which was derived from arcs built on the Wrangellia composite terrane during the Late Jurassic to Early Cretaceous. A newly discovered locality of Alaska-type zoned ultramafic bodies within the Clearwater metasediments provides an additional link to the Wrangellia composite terrane. The Maclaren and Clearwater metasedimentary belts are presently juxtaposed by the newly identified Valdez Creek fault, which is an upper crustal reactivation of the Valdez Creek shear zone, the Late Cretaceous plate boundary that initially brought them together. 40Ar/39Ar mica ages reveal independent post-collisional thermal histories of hanging wall and footwall rocks until reactivation localized on the Valdez Creek fault after ca. 32 Ma. Slip on the Valdez Creek fault expanded into a thrust system that progressed southward to the Broxson Gulch fault at the southern margin of the suture zone and eventually into the Wrangellia terrane. Detrital zircon U-Pb age spectra and clast assemblages from fault-bounded Cenozoic gravel deposits indicate that the thrust system was active during the Oligocene and into the Pliocene, likely as a far-field result of ongoing flat-slab subduction and accretion of the Yakutat microplate. The Valdez Creek fault was the primary reactivated structure in the suture zone, likely due to its linkage with the reactivated boundary zone between the Wrangellia composite terrane and North America in the lithospheric mantle.

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Record of Crustal Thickening and Synconvergent Extension from the Dajiamang Tso Rift, Southern Tibet

Geosciences ◽

10.3390/geosciences11050209 ◽

2021 ◽

Vol 11 (5) ◽

pp. 209

Author(s):

William B. Burke ◽

Andrew K. Laskowski ◽

Devon A. Orme ◽

Kurt E. Sundell ◽

Michael H. Taylor ◽

...

Keyword(s):

Dynamic Models ◽

Hanging Wall ◽

Crustal Thickness ◽

Suture Zone ◽

Crustal Thickening ◽

Southern Tibet ◽

South Central ◽

Crustal Thinning ◽

Indian Lithosphere ◽

Central Tibet

North-trending rifts throughout south-central Tibet provide an opportunity to study the dynamics of synconvergent extension in contractional orogenic belts. In this study, we present new data from the Dajiamang Tso rift, including quantitative crustal thickness estimates calculated from trace/rare earth element zircon data, U-Pb geochronology, and zircon-He thermochronology. These data constrain the timing and rates of exhumation in the Dajiamang Tso rift and provide a basis for evaluating dynamic models of synconvergent extension. Our results also provide a semi-continuous record of Mid-Cretaceous to Miocene evolution of the Himalayan-Tibetan orogenic belt along the India-Asia suture zone. We report igneous zircon U-Pb ages of ~103 Ma and 70–42 Ma for samples collected from the Xigaze forearc basin and Gangdese Batholith/Linzizong Formation, respectively. Zircon-He cooling ages of forearc rocks in the hanging wall of the Great Counter thrust are ~28 Ma, while Gangdese arc samples in the footwalls of the Dajiamang Tso rift are 16–8 Ma. These data reveal the approximate timing of the switch from contraction to extension along the India-Asia suture zone (minimum 16 Ma). Crustal-thickness trends from zircon geochemistry reveal possible crustal thinning (to ~40 km) immediately prior to India-Eurasia collision onset (58 Ma). Following initial collision, crustal thickness increases to 50 km by 40 Ma with continued thickening until the early Miocene supported by regional data from the Tibetan Magmatism Database. Current crustal thickness estimates based on geophysical observations show no evidence for crustal thinning following the onset of E–W extension (~16 Ma), suggesting that modern crustal thickness is likely facilitated by an underthrusting Indian lithosphere balanced by upper plate extension.

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New insights into the polyphase evolution of the Variscan suture zone: evidence from the Staré Město Belt, NE Bohemian Massif

Geological Magazine ◽

10.1017/s0016756812000040 ◽

2012 ◽

Vol 149 (6) ◽

pp. 945-963 ◽

Cited By ~ 7

Author(s):

MIROSŁAW JASTRZĘBSKI

Keyword(s):

Bohemian Massif ◽

Hanging Wall ◽

Suture Zone ◽

Peak Temperature ◽

Structural Studies ◽

Metasedimentary Rocks ◽

Axial Part ◽

Thrust Zone ◽

Continuous Indentation ◽

Middle Unit

AbstractForming a northern continuation of the Moldanubian Thrust Zone, the Staré Město Belt comprises an E-verging thrust stack of three narrow lithotectonic units that exhibit variations in their respective P–T records. The upper and lower units form the respective margins of the hanging wall and footwall of the suture zone and are dominated by amphibolite grade metasedimentary successions. The middle unit is defined by an elongated body of MORB-like amphibolites that contains inserts of migmatized mica schists. Integrating both structural studies and pseudosection modelling in the MnNCKFMASH system shows that the present-day tectonic architecture of the Staré Město Belt is the result of a polyphase Variscan evolution. During a frontal, WNW–ESE-directed (in present-day coordinates) collision between the Bohemian Massif terranes and the Brunovistulian terrane, the metasedimentary rocks of the Staré Město Belt experienced tectonic burial to depths corresponding to 7–9 kbar. The continuous indentation and underthrusting of the Brunovistulian terrane led to top-to-the-ESE folding and uplift of these rocks to depths corresponding to 5.5–6.0 kbar at peak temperature. At depths corresponding to 5.5 kbar, the Staré Město Belt underwent subsequent dextral (top-to-the-NNE) shearing that was locally associated with nearly isobaric heating, possibly related to the emplacement of a Carboniferous tonalite body in the axial part of the Staré Město Belt. Subsequent tectonic compression resulted in the Variscan WNW-dipping metamorphic foliations becoming locally (N)NE- or ESE-dipping.

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Late Paleozoic extensional reactivation of the Rheic–Rhenohercynian suture zone in SW England, the English Channel and Western Approaches

Geological Society London Special Publications ◽

10.1144/sp470.19 ◽

2019 ◽

Vol 470 (1) ◽

pp. 353-373 ◽

Cited By ~ 1

Author(s):

Andrew C. Alexander ◽

Robin K. Shail ◽

Brian E. Leveridge

Keyword(s):

Hanging Wall ◽

Shear Zones ◽

Suture Zone ◽

Passive Margin ◽

Lower Plate ◽

Early Permian ◽

Plate Convergence ◽

Rheic Ocean ◽

Detachment Faults ◽

And Inversion

AbstractThe Rheic Ocean is a persistent feature of Paleozoic palaeogeographies whose closure contributed to the development of the Variscan Orogen and the formation of Pangaea. Geological and geophysical data indicate repeated episodes of Paleozoic rifting and plate convergence around SW England and the adjacent offshore areas. SW England occupied a lower plate position during the Devonian–Carboniferous, on the northern passive margin of the short-lived Rhenohercynian Ocean that had formed near a recently closed segment of the Rheic Ocean. Variscan plate convergence resulted in the development of the composite southwards-dipping Rheic–Rhenohercynian suture zone by the latest Devonian and inversion of the lower plate basins during the Carboniferous. Early Permian NNW–SSE extensional reactivation of this suture zone controlled the development of the Western Approaches basins in its hanging wall and provides an excellent example of Wilson cycle structural inheritance. The onshore expression of this episode includes shear zones and detachment faults consistent with top-to-the-SSE extensional reactivation of Variscan thrust faults. There is a progression to higher-angle brittle extensional faults that cut out earlier structures. Exhumation of the lower plate was accompanied by Early Permian mantle and concomitant crustal partial melting, the construction of the Cornubian Batholith and W–Sn–Cu fracture-hosted mineralization.

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Crustal magnetization variations across the Iapetus Suture Zone

Geological Magazine ◽

10.1017/s0016756800021257 ◽

1995 ◽

Vol 132 (5) ◽

pp. 599-609 ◽

Cited By ~ 23

Author(s):

G. S. Kimbell ◽

P. Stone

Keyword(s):

Hanging Wall ◽

Suture Zone ◽

Lake District ◽

The South ◽

Long Wavelength ◽

The North ◽

Anomaly Pattern ◽

Magnetic Basement ◽

Crustal Magnetization ◽

Structural Levels

AbstractThe Iapetus Suture (Solway) line coincides with a magnetic low, which lies between magnetic highs over southwestern Scotland and the Lake District-Isle of Man region. Although topography on deep magnetic basement can account for these long wavelength geophysical variations, an explanation which involves lateral basement magnetization contrasts is preferred on the basis of (a) correlations between inferred magnetization boundaries and major structures delineated from other evidence, and (b) the apparent westward continuation of the Solway low through Ireland and Newfoundland across areas with very different subsidence histories but similar position with respect to the collision of Laurentia and Avalonia. In the preferred model, relatively magnetic continental crust beneath the Southern Uplands and Lake District terranes is separated by a zone of less magnetic crust interpreted as sedimentary rock of Avalonian affinity carried to deeper structural levels within the Iapetus Suture Zone. The magnetic unit beneath the Southern Uplands is bounded to the south by the northward-dipping Iapetus Suture and to the north by a structure which may have been reactivated in late Caledonian times to produce the Moniaive Shear Zone in the overlying rocks; this unit may represent the ‘missing’ arc terrane inferred from provenance studies. Alternatively, the two magnetic basement domains may have originally been part of the same terrane, with that portion beneath the Southern Uplands rifting from the Avalonian continent during its northwards drift and being subsequently trapped in the hanging wall of the Iapetus Suture. The southern margin of the Lake District domain appears as a discontinuity in the magnetic anomaly pattern, with long wavelength anomalies to the south having a southeast ‘Tornquist’ trend.

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