T.H. Bell

Centre for Addiction and Mental Health

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Kenneth A. Hickey

University of British Columbia

A. Forde

James Cook University

Nicholas Hayward

University of Western Australia

Scott E. Johnson

Beth Israel Deaconess Medical Center

A.P. Ham

James Cook University

M. J. Rubenach

James Cook University

C. Fay

James Cook University

Ioan V. Sanislav

James Cook University

Hyeong Soo Kim

Korea University

J. Wang

James Cook University

Cooperative Institutions

James Cook University

University of Leeds

Geological Survey of Western Australia

Australian National University

Imperial College London

University of Manchester

Centre National de la Recherche Scientifique

Mineral Resources

Instituto Andaluz de Ciencias de la Tierra

Universidad de Granada

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Episodic gravitational collapse and migration of the mountain chain during orogenic roll‐on in the Himalayas

Journal of Metamorphic Geology (2012)

T.H. Bell Jyotindra Sapkota

Abstract An ∼W–E belt of maximum bulk horizontal shortening (the orogen core) moved North relative to the overlying crust to form the Himalayan Syntaxes due to roll‐on of this portion of the Indian plate. This displacement occurred below a lengthy succession of gently dipping decollements that formed episodically at a depth of ∼30 km along the orogen core due to numerous periods of gravitational collapse and spreading of the overlying ductile crust. Successively developed basal decollements were deformed when continued bulk horizontal shortening of the orogen core below reasserted dominance over the effects of gravitational collapse above causing refolding about steeply dipping axial planes. This resulted in northwards migration of the orogen core above depths of ∼30 km causing rocks metamorphosing at depths of ∼22 km on the north side of the orogen core to be moved to its south side with no change in depth as roll‐on progressed. Garnet porphyroblasts record this lengthy history of lateral migration across the orogen within their inclusion trails. The ∼6.4 kbar average pressures accompanying it were obtained from the Mn, Fe and Ca contents of successive garnet cores. Garnet grew at depths of ∼22 km until movement towards the surface initiated on successively developed decollements that accommodated the volume constraints of gravitational collapse and spreading on both sides of the orogen. The speed of extrusional displacement increased the further the rocks migrated from the orogen core developing mylonitic schists around the porphyroblasts. This truncated inclusion trails against all matrix foliations as the porphyroblasts were carried towards the surface. Indeed, these rocks were multiply deformed during at least four distinct periods of deformation after mylonitization began and prior to exposure above the Main Central Thrust (MCT). Three or more sub‐vertical and sub‐horizontal foliations were formed during each of the five changes in FIA trend (foliation inflection/intersection axes in porphyroblasts) preserved in these rocks. The inclusion trail asymmetries and P‐T of garnet core growth accompanying each FIA reveal that the first four changes in FIA trend, which define periods of tectonism about one direction of horizontal bulk shortening (relative plate motion), occurred on the north side of the orogen core. The fifth occurred on the south side of the orogen core and the switch in shear sense on gently dipping foliation planes that resulted from this shift to the south eventually led to the development of the MCT. When magnetic anomaly 22 that formed in the Southern Indian Ocean Ridge is taken into account, these five changes in FIA trend correlate markedly with changes in the motion of India relative to a constant Eurasia from 50 to c. 25 Ma. They reveal that Eurasia moved NNW during FIAs 1, 3 and 4 and SSE during FIA 5 when the shear sense on gently dipping foliations switched to top to the S. They suggest collision of India with Eurasia took place at 50 Ma, immediately prior to the development of FIA 1.

Overprinting

10.1111/j.1525-1314.2012.00992.x

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Citations (30)

Thrusting and duplex formation at Mount Isa, Queensland, Australia

Nature (1983)

T.H. Bell

Mount

Anticline

Duplex (building)

Trough (economics)

10.1038/304493a0

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Citations (110)

Porphyroblast inclusion‐trail orientation data: eppure non son girate*!

Journal of Metamorphic Geology (1992)

T.H. Bell Scott E. Johnson B. K. Davis A. Forde Nicholas Hayward

Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non‐coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens.

Lineation

Overprinting

10.1111/j.1525-1314.1992.tb00084.x

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Citations (134)

Microstructural controls on sites of metamorphic reaction: a case study of the inter-relationship between deformation and metamorphism

European Journal of Mineralogy (1996)

Richard Spiess T.H. Bell

10.1127/ejm/8/1/0165

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Citations (55)

Structural controls on development and localization of syntectonic copper mineralization at Mount Isa, Queensland

Economic Geology (1988)

T.H. Bell W. G. Perkins C.P. Swager

Other| February 01, 1988 Structural controls on development and localization of syntectonic copper mineralization at Mount Isa, Queensland T. H. Bell; T. H. Bell James Cook Univ., Dep. Geol., Townsville, Queensl., Australia Search for other works by this author on: GSW Google Scholar W. G. Perkins; W. G. Perkins Search for other works by this author on: GSW Google Scholar C. P. Swager C. P. Swager Search for other works by this author on: GSW Google Scholar Author and Article Information T. H. Bell James Cook Univ., Dep. Geol., Townsville, Queensl., Australia W. G. Perkins C. P. Swager Publisher: Society of Economic Geologists First Online: 02 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 GeoRef, Copyright 2006, American Geological Institute. Abstract, Copyright, Society of Economic Geologists Economic Geology (1988) 83 (1): 69–85. https://doi.org/10.2113/gsecongeo.83.1.69 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation T. H. Bell, W. G. Perkins, C. P. Swager; Structural controls on development and localization of syntectonic copper mineralization at Mount Isa, Queensland. Economic Geology 1988;; 83 (1): 69–85. doi: https://doi.org/10.2113/gsecongeo.83.1.69 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract Three major deformation events were responsible for the structural relationships in the Mount Isa mine where steeply west-dipping siliceous and dolomitic sediments of the Mount Isa Group, which host the Ag-Pb-Zn ores as well as the epigenetic Cu orebodies, are truncated against the underlying greenschists. The Cu orebodies and their alteration envelope, the silica dolomite, developed during the third deformation (D 3 ) within the dolomitic Urquhart Shale, adjacent to this greenschist contact.This contact is a fault that formed during thrusting in D 1 and was rotated and overturned by the combined effects of D 1 and D 2 into a shallowly dipping attitude on the western limb of a regional-scale upright D 2 antiform. Consequently it lay at a high angle to the steeply plunging stretching direction established during the third deformation (D 3 ). This fault was a plane of considerable anisotropy and competency contrast because the rocks above were dolomitic siltstones whereas those below were greenschists, with bedding respectively at a high angle and subparallel to the fault.Folding during D 3 generated opposed senses of shear and hence differential movement across the fault, especially at fold hinges. This, in combination with the differential anisotropy and competency contrast across the fault, and extension at a high angle to it, resulted in localized fracture and opening of the contact and consequently a rapid drop in fluid pressure, possibly on several occasions in different locations along the greenschist contact. The large imbalance in fluid pressure across the walls of these localized openings caused explosive fracturing and local brecciation, especially of the dolomitic rocks on the fault walls into the space created. This provided access for the syndeformation hydrothermal fluid to all faces of the jostled blocks of dolomitic shales enabling their alteration to form the silica dolomite and the Cu ores. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Mount

10.2113/gsecongeo.83.1.69

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Citations (52)

Holistic microstructural techniques reveal synchronous and alternating andalusite and staurolite growth during three tectonic events resulted from shifting partitioning of growth vs deformation

Lithos (2016)

T.H. Bell C. Fay

Andalusite

Staurolite

Overprinting

Coaxial

10.1016/j.lithos.2016.06.031

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Citations (20)

Microstructural controls and the role of graphite in matrix/ porphyroblast exchange during synkinematic andalusite growth in a granitoid aureole

Journal of Metamorphic Geology (1988)

M. J. Rubenach T.H. Bell

Abstract In the contact metamorphic aureole of the Tinaroo Batholith (north Queensland, Australia), mylonitic rocks were metamorphosed during a regional folding/crenulation event ( D 2 ) synchronous with the emplacement of muscovite‐bearing granitoids. Prismatic and skeletal andalusite porphyoblasts grew in carbonaceous schists, mainly from the dissolution of staurolite. Muscovite, quartz and biotite played a dual role in this reaction, acting in a catalytic capacity as well as reactants or products. Staurolite was replaced by coarse‐grained muscovite ± biotite, whereas andalusite locally replaced quartz ± muscovite ± biotite, with diffusion of H, Al, Si, Mg, Fe and K ionic species linking sites of dissolution and growth. Graphite contributed to the reaction mechanism in a number of ways. Accumulations of graphite in front of advancing andalusite crystal faces led to skeletal growth and the formation of chiastolite structure, where incremental growth occurred on adjacent {110} faces, with subsequent filling in and inclusion of graphite along the diagonal zones. The presence of graphite in some layers in the schist matrix prevented recrystallization of strained muscovite grains. The muscovite grains in these layers, in contrast to adjacent thin non‐graphitic layers, were preferentially replaced by quartz. This resulted in muscovite‐depletion haloes in graphitic layers around andalusite porphyroblasts. Somewhat arcuate zones of graphite, concentrated during dissolution of quartz along a crenulation cleavage, occur on some andalusite faces. Reactivation of the mylonitic foliation during the formation of D 2 crenulations led to a preferential dissolution of quartz in zones of progressive shearing localized near andalusite porphyroblasts and hence the accumulation of graphite. Lack of deflection of the pre‐existing mylonitic foliation and anastomosing of the axial planes of D 2 crenulations around andalusite porphyroblasts demonstrate not only the timing of growth, but also that growing porphyroblasts do not push aside existing foliations.

Andalusite

Muscovite

Staurolite

Crenulation

Mylonite

Sillimanite

10.1111/j.1525-1314.1988.tb00446.x

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Citations (41)

Three-Dimensional Seismic-Wave Gradiometry for Scalar Waves

Bulletin of the Seismological Society of America (2013)

Christian Poppeliers Predrag Punoševac T.H. Bell

Wave gradiometry relates the spatial gradients of a wavefield to its velocity and radiation patterns through two spatial coefficients for any dimension. One coefficient gives the slowness of the wave in any given dimension, and the other coefficient gives the change in amplitude as a function of position and direction along the wavefront. In this paper, we develop the mathematical foundations for scalar wave gradiometry in three dimensions, building on previous work in 1D and 2D wave gradiometry. We validate our method by synthetic tests and find that our method can accurately estimate wave direction and speed. Estimating spatial amplitude changes is not as robust, however. Numerical tests indicate that the wave gradiometry method is highly sensitive to uncorrelated noise in the data as well as the presence of interfering waves.

10.1785/0120120224

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Citations (15)

The role of thrusting in the structural development of the Mount Isa Mine and its relevance to exploration in the surrounding region; reply

Economic Geology (1993)

T.H. Bell

Mount

Relevance

10.2113/gsecongeo.88.2.479

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Citations (0)

The role of thrusting in the structural development of the Mount Isa Mine and its relevance to exploration in the surrounding region; reply