Lower crustal melting and the role of open-system processes in the genesis of syn-orogenic quartz diorite–granite–leucogranite associations: constraints from Sr–Nd–O isotopes from the Bandombaai Complex, Namibia

Lithos ◽  
2003 ◽  
Vol 67 (3-4) ◽  
pp. 205-226 ◽  
Author(s):  
Tina van de Flierdt ◽  
Stephan Hoernes ◽  
Stefan Jung ◽  
Peter Masberg ◽  
Edgar Hoffer ◽  
...  
Keyword(s):  
Open System ◽  
Quartz Diorite ◽  
Crustal Melting ◽  
O Isotopes ◽  
Lower Crustal

Plumbing and architecture of a crustal mineralizing system in the Archean Superior Province, Canada

2021 ◽  
Author(s):  
Eric Roots ◽  
Graham Hill ◽  
Ben M. Frieman ◽  
James A. Craven ◽  
Richard S. Smith ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Spatial Association ◽  
Three Dimensional ◽  
3D Models ◽  
Superior Province ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Abitibi Subprovince ◽  
Lower Crustal

<p>The role of melts and magmatic/metamorphic fluids in mineralization processes is well established. However, the role of crustal architecture in defining source and sink zones in the middle to lower crust remains enigmatic. Integration of three dimensional magnetotelluric (MT) modelling and seismic reflection data across the Archean Abitibi greenstone belt of the Superior Province, Canada, reveals a ‘whole-of-crust’ mineralizing system and highlights the controls by crustal architecture on metallogenetic processes. Electrically conductive conduits in an otherwise resistive upper crust are coincident with truncations and offsets of seismic reflections that are mostly interpreted as major brittle-ductile fault zones. The spatial association between these features and low resistivity zones imaged in the 3D models suggest that these zones acted as pathways through which fluids and melts ascended toward the surface. At mid-crustal levels, these ‘conduit’ zones connect to ~50 km long, north-south striking conductors, and are inferred to represent graphite and/or sulphide deposited from cooling fluids. At upper mantle to lower crustal depths, east-west trending conductive zones dominate and display shallow dips. The upper mantle features are broadly coincident with the surface traces of the major deformation zones with which a large proportion of the gold endowment is associated. We suggest that these deep conductors represent interconnected graphitic zones perhaps augmented by sulphides that are relicts from metamorphic fluid and melt emplacement associated primarily with the later stages of regional deformation.  Thus, from the combined MT and seismic data, we develop a crustal-scale architectural model that is consistent with existing geological and deformational models, providing constraints on the sources for and signatures of fluid and magma emplacement that resulted in widespread metallogenesis in the Abitibi Subprovince.</p>

An open system approach to higher learning: the role of joint ventures with business

2000 ◽  
Vol 100 (5) ◽  
pp. 227-233 ◽  
Author(s):  
Mahmoud M. Yasin ◽  
Andrew J. Czuchry ◽  
James Martin ◽  
Ray Feagins
Keyword(s):  
Open System ◽  
Joint Ventures ◽  
System Approach ◽  
Higher Learning

scholarly journals The Role of Lower Crustal Rheology in Lithospheric Delamination During Orogeny

2021 ◽  
Vol 9 ◽  
Author(s):  
Lin Chen
Keyword(s):  
Lower Crust ◽  
Numerical Models ◽  
The Tibetan Plateau ◽  
Mantle Lithosphere ◽  
Laboratory Studies ◽  
Surface Uplift ◽  
Continental Lower Crust ◽  
Lower Crustal ◽  
Flow Laws

The continental lower crust is an important composition- and strength-jump layer in the lithosphere. Laboratory studies show its strength varies greatly due to a wide variety of composition. How the lower crust rheology influences the collisional orogeny remains poorly understood. Here I investigate the role of the lower crust rheology in the evolution of an orogen subject to horizontal shortening using 2D numerical models. A range of lower crustal flow laws from laboratory studies are tested to examine their effects on the styles of the accommodation of convergence. Three distinct styles are observed: 1) downwelling and subsequent delamination of orogen lithosphere mantle as a coherent slab; 2) localized thickening of orogen lithosphere; and 3) underthrusting of peripheral strong lithospheres below the orogen. Delamination occurs only if the orogen lower crust rheology is represented by the weak end-member of flow laws. The delamination is followed by partial melting of the lower crust and punctuated surface uplift confined to the orogen central region. For a moderately or extremely strong orogen lower crust, topography highs only develop on both sides of the orogen. In the Tibetan plateau, the crust has been doubly thickened but the underlying mantle lithosphere is highly heterogeneous. I suggest that the subvertical high-velocity mantle structures, as observed in southern and western Tibet, may exemplify localized delamination of the mantle lithosphere due to rheological weakening of the Tibetan lower crust.

The role of magmatic reaction, diffusion, and annealing in the evolution of coronitic microstructure in troctolitic gabbro from Risör, Norway: a discussion

1986 ◽  
Vol 50 (357) ◽  
pp. 469-473 ◽  
Author(s):  
J. R. Ashworth
Keyword(s):  
Solid State ◽  
Open System ◽  
Local Equilibrium ◽  
Reaction Diffusion ◽  
One Dimension ◽  
System Behaviour ◽  
Diffusion Controlled

AbstractThe data of Joesten (1986) are re-interpreted. The petrography of the coronas is not consistent with magrnatic origin. Both microstructural types described by Joesten (1986), here re-named ‘columnar’ and ‘tabular’, formed by solid-state replacement of plagioclase and of adjacent olivine or ilmenite. Tabular microstructures are not annealed, but result from overgrowth or epitaxy of amphibole and pyroxene on pre-existing grains. Since the diffusion-controlled models of Joesten (1986) can account for major aspects of the coronas, it seems possible that a slightly modified, less simplified theory might explain them fully. Open-system behaviour must be admitted, with some constraints provided by symplectites. It may also be necessary to develop the theory in more than one dimension, and to allow for departures from local equilibrium at layer boundaries.

Role of crustal and slab components in the Northern Volcanic Zone of the Andes (Ecuador) constrained by Sr–Nd–O isotopes

Lithos ◽  
2012 ◽  
Vol 132-133 ◽  
pp. 180-192 ◽  
Author(s):  
Silvana Hidalgo ◽  
Marie C. Gerbe ◽  
Hervé Martin ◽  
Pablo Samaniego ◽  
Erwan Bourdon
Keyword(s):  
Volcanic Zone ◽  
The Andes ◽  
O Isotopes ◽  
Northern Volcanic Zone

Evidence from borehole samples for the role of accessory minerals in lower-crustal conductivity

Nature ◽  
1994 ◽  
Vol 367 (6458) ◽  
pp. 59-61 ◽  
Author(s):  
A. Duba ◽  
S. Heikamp ◽  
W. Meurer ◽  
G. Mover ◽  
G. Will
Keyword(s):  
Accessory Minerals ◽  
Lower Crustal

scholarly journals Bimodality of Lavas in the Teide-Pico Viejo Succession in Tenerife--the Role of Crustal Melting in the Origin of Recent Phonolites

2012 ◽  
Vol 53 (12) ◽  
pp. 2465-2495 ◽  
Author(s):  
S. Wiesmaier ◽  
V. R. Troll ◽  
J. C. Carracedo ◽  
R. M. Ellam ◽  
I. Bindeman ◽  
...  
Keyword(s):  
Crustal Melting

Late Jurassic, high Ba–Sr Linglong granites in the Jiaodong Peninsula, East China: lower crustal melting products in the eastern North China Craton

2017 ◽  
Vol 155 (5) ◽  
pp. 1040-1062 ◽  
Author(s):  
LI-QIANG YANG ◽  
YILDIRIM DILEK ◽  
ZHONG-LIANG WANG ◽  
ROBERTO F. WEINBERG ◽  
YUE LIU
Keyword(s):  
North China Craton ◽  
Late Jurassic ◽  
North China ◽  
Eastern China ◽  
Ultrahigh Pressure ◽  
Granitic Rocks ◽  
Crustal Melting ◽  
Heavy Rare Earth Element ◽  
The North ◽  
Lower Crustal

AbstractThe Jurassic Linglong granites, intrusive into the North China Craton (NCC) in eastern China, provide a critical record of the first major episode of lithospheric-scale extension and magmatism in NE China during Mesozoic time. Our U–Pb zircon dating reveals that the Linglong granites were emplaced during 161–158 Ma, shortly after the inception of a shallow subduction of the Palaeo-Pacific plate beneath East Asia during Middle Jurassic time. These granites have high alkali contents (K2O + Na2O = 8–9 wt%), low MgO and Mg no. values and variable Cr–Ni abundances. Their relatively high Ba and Sr concentrations, relatively low heavy rare Earth element (HREE) and strongly fractionated REE patterns characterize them as high Ba–Sr granites. The negative whole-rock εNd(t) values ranging from −22.4 to −10.9 and wide-ranging zircon εHf(t) values of −39.1 to −1.5 suggest that magmas of the Linglong granites were produced by partial melting of a garnet-amphibolite-bearing lower crust of the Jiaobei Terrane and by re-melting of the Triassic ultrahigh-pressure (UHP) metamorphic rocks and alkaline suites of the Sulu Terrane. The occurrence in the granitic rocks of inherited zircons of the Neoarchaean, Palaeoproterozoic, Neoproterozoic, Palaeozoic and Triassic ages suggests that magmas of the Linglong granites interacted with the ancient crust in these terranes during their ascent. Asthenospheric upwelling, induced by the steepening and rapid rollback of the Palaeo-Pacific slab during Late Jurassic time, provided the heat source for the inferred lower crustal melting. Trench migration and thermal weakening of the crust caused extensional deformation and thinning in the eastern part of the NCC.

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