Improving drug solubility for oral delivery using solid dispersions.

Orogenic gold and geologic time: a global synthesis

(1976). Nuclear Tracks in Solids (Principles and Applications) Nuclear Technology: Vol. 30, No. 1, pp. 91-92.

Nuclear Tracks in Solids (Principles and Applications)

This paper deals with the various tectonic units in the Chinese Eastern Tianshan orogenic collage in the Central Asian Orogenic Belt, and discusses the Paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the Tarim and southern Angaran continental margins. The Late Ordovician-Silurian to Early Devonian Eastern Tianshan archipelago was characterized by (a) the Harlik-Dananhu subduction system with a S-dipping polarity in the north; (b) a southerly N-dipping subduction system beneath the Central Tianshan arc in the middle; and (c) the South Tianshan ocean against Tarim in the south. During the Devonian to Early Carboniferous, N-dipping subduction led to the Harlik-Dananhu arc and the Kanggurtag forearc basin/accretionary complex. In the Early to Mid-Carboniferous, the magmatic front associated with the N-dipping subduction beneath the Dananhu-Harlik arc migrated southwards, forming the Yamansu arc constructed upon the Kanggurtag accretionary forearc. By the Late Carboniferous the Dananhu-Harlik arc was attached northwards to the Angaran margin, resulting in lateral enlargement of the Angaran continent. In the latest Carboniferous to Early Permian a multiple soft collision left wide suture zones in the south that include the ophiolite-strewn Aqikkuduk-Shaquanzi and Kumishi accretion-collision complexes, which were stitched by Early Permian post-collisional plutons. By re-defining and re-interpreting the various tectonic terranes, this paper presents a new, improved model for the Paleozoic evolution of this part of Central Asia.

Paleozoic accretionary and collisional tectonics of the Eastern Tianshan (China): Implications for the continental growth of Central Asia

Metamorphic belts are complex regions where accretion or collision has added
to, or thickened, continental crust. Gold-rich deposits can be formed at all
stages of orogen evolution, so that evolving metamorphic belts contain diverse
gold deposit types that may be juxtaposed or overprint each other. This partly
explains the high level of controversy on the origin of some deposit types,
particularly those formed or overprinted/remobilized during the major
compressional orogeny that shaped the final geometry of the hosting metamorphic
belts. These include gold-dominated orogenic and intrusion-related deposits, but
also particularly controversial gold deposits with atypical metal associations. Orogenic lode gold deposits of Middle Archean to Tertiary age are arguably
the predominant gold deposit type in metamorphic belts, and include several
giant (>250 t Au) and numerous world-class (>100 t Au) examples. Their
defining characteristics and spatial and temporal distributions are now
relatively well documented, such that other gold deposit types can be compared
and contrasted against them. They form as an integral part of the evolution of
subduction-related accretionary or collisional terranes in which the host-rock
sequences were formed in arcs, back arcs, or accretionary prisms. Current
unknowns for orogenic gold deposits include the following: (1) the precise
tectonic setting and age of mineralization in many provinces, particularly in
Paleozoic and older metamorphic belts; (2) the source of ore fluids and metals;
(3) the precise architecture of the hydrothermal systems, particularly the
relationship between first- and lower-order structures; and (4) the specific
depositional mechanisms for gold, particularly for high-grade deposits. Gold-dominant intrusion-related deposits are a less coherent group of
deposits, which are mainly Phanerozoic in age, and include a few world-class,
but no unequivocal giant, examples. They have many similarities to orogenic
deposits in terms of metal associations, wall-rock alteration assemblages, ore
fluids, and, to a lesser extent, structural controls, and hence, some deposits,
particularly those with close spatial relationships to granitoid intrusions,
have been placed in both orogenic and intrusion-related categories by different
authors. Those that are clearly intrusion-related deposits appear to be best
distinguished by their near-craton setting, in locations more distal from
subduction zones than most orogenic gold deposits and in provinces that also
commonly contain Sn and/or W deposits; relatively low gold grades (<1–2
g/t Au); and district-scale zoning to Ag-Pb-Zn deposits in distal zones.
Outstanding problems for intrusion-related deposits include the following: (1)
lack of a clear definition of this apparently diverse group of deposits, (2)
lack of a definitive link for ore fluids and metals between mineralization and
magmatism, (3) the diverse nature of both petrogenetic association and redox
state of the granitoids invoked as the source of mineralization, and (4)
mechanisms for exsolution of the CO 2 -rich ore fluids from the
relatively shallow level granitoids implicated as ore-fluid sources. Gold deposits with atypical metal associations are a particularly diverse and
controversial group, are most abundant in Late Archean terranes, and include
several world-class to giant examples. Most are probably modified Cu-Mo-Au
porphyry, volcanic rock-hosted Zn-Pb-Ag-Au massive sulfide, or Zn-Pb-Ag-Au or
Ba-Au-Mo-Hg submarine epithermal systems, overprinted or remobilized during the
events in which orogenic gold deposits formed, but there is lack of consensus on
genesis. Outstanding problems for these deposits include the following: (1) lack
of a clear grouping of distinctive deposits, (2) lack of published, well
integrated studies of their characteristics, (3) generally a poorly defined
timing of mineralization events, and (4) lack of assessment of metal mass
balances in each stage of the complex mineralization and overprinting events. Both orogenic gold deposits and gold deposits with atypical metal
associations contain a few giant and numerous world-class examples, whereas the
intrusion-related group contains very few world-class examples, and no giants,
unless Muruntau is included in this group. Preliminary analysis suggests that
the parameters of individual world-class to giant gold deposits of any type show
considerable variation, and that it is impossible to define critical factors
that control their size and grade at the deposit scale. However, there appears
more promise at the terrane to province scale where there are greater
indications of common factors such as anomalous subduction-related tectonic
settings, reactivated crustal-scale deformation zones that focus porphyry-lamprophyre
dike swarms in linear volcanosedimentary belts, complex regional-scale geometry
of mixed lithostratigraphic packages, and evidence for multiple mineralization
or remobilization events. There are a number of outstanding problems for all types of gold deposits in
metamorphic belts. These include the following: (1) definitive classifications,
(2) unequivocal recognition of fluid and metal sources, (3) understanding of
fluid migration and focusing at all scales, (4) resolution of the precise role
of granitoid magmatism, (5) precise gold-depositional mechanisms, particularly
those producing high gold grades, and (6) understanding of the release of CO 2 -rich
fluids from subducting slabs and subcreted oceanic crust and granitoid magmas at
different crustal levels. Research needs to be better coordinated and more
integrated, such that detailed fluid-inclusion, trace-element, and isotopic
studies of both gold deposits and potential source rocks, using cutting-edge
technology, are embedded in a firm geological framework at terrane to deposit
scales. Ultimately, four-dimensional models need to be developed, involving
high-quality, three-dimensional geological data combined with integrated
chemical and fluid-flow modeling, to understand the total history of the
hydrothermal systems involved. Such research, particularly that which can
predict superior targets visible in data sets available to exploration companies
before discovery, has obvious spin-offs for global- to deposit-scale targeting
of deposits with superior size and grade in the covered terranes that will be
the exploration focus of the twenty-first century.

/pdf/gold-deposits-in-metamorphic-belts-overview-of-current-pxhffwpeq8.pdf

Gold Deposits in Metamorphic Belts: Overview of Current Understanding,Outstanding Problems, Future Research, and Exploration Significance

In Gobi Altay and Altay, Mongolia, several flat surfaces, worn through basement rocks and uplifted during the ongoing tectonic episode to a similar altitude of 4000 m, suggests disruption of a single large-scale surface. New thermochronology and field data show that the plateau surfaces represent uplifted parts of an ancient peneplain that formed during Jurassic time. The Gobi Altay and Altay flattopped massifs are tectonically and geomorphologically unique. Their preservation for ~150 m.y. implies that no further tectonic movements occurred before the onset of the last deformation episode, 5 ± 3 m.y. ago. It also suggests that very low erosion rates were maintained by a dry climate over millions of years.

https://perso-sdt.univ-brest.fr/~jacdev/pdf/jolivet07.pdf

Mongolian summits: An uplifted, flat, old but still preserved erosion surface

Plate interface rheological switches during subduction infancy: Control on slab penetration and metamorphic sole formation

Extension-parallel folding in the Scandinavian Caledonides: Implications for late-orogenic processes

[1] The South Portuguese Zone (SPZ) constitutes the southernmost segment of the Variscan Iberian Massif. It is bounded to the north by the Beja-Acebuches Ophiolitic Complex and related accretionary wedge. To the south lie the Iberian Pyrite Belt (IPB) and flysch deposits forming the southern extent of the zone. Structural analysis within the Spanish side of the SPZ supports continuous south propagating deformation, evolving from early synmetamorphic thrusting in the internal zone to thin-skinned tectonics in the southern external domain. The accretion of the SPZ to the Ossa Morena Zone is also witnessed by the presence of various melanges, observed throughout the investigated area. Part of the melanges observed in the IPB are related to the volcanics and mineralizations setting. A key point to understand the IPB mineralizations genesis is to constrain the volcanogenic model. One underestimated feature is the large amount of submarine calc-alkaline ignimbritic facies, implying the presence of caldera structures within the province. Such correlation between caldera environment and ore deposits strongly suggests that the IPB developed in a continental arc. Our geodynamic model proposes an early north directed subduction associated with the obduction of the oceanic crust toward the south. Southward, this episode is immediately followed by the development of the accretionary prism, while farther south, a second subduction zone responsible for the arc setting of the IPB initiates. Subsequent Visean continental collision is associated with the deposit of the south propagating flysch and the present geometry of the SPZ.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002TC001387

A new geodynamic interpretation for the South Portuguese Zone (SW Iberia) and the Iberian Pyrite Belt genesis

Pure-shear and simple-shear models provide interpretations of sedimentary basins formed by extension of crust and lithosphere of normal thickness. Devonian basins of western Norway developed during collapse of the thickened Caledonian crust and return to a crust and lithosphere of normal thickness. Because extension did not thin the lithosphere to less than its normal thickness, no thermal subsidence phase followed the initial subsidence.

Alain Chauvet

Papers

Mongolian summits: An uplifted, flat, old but still preserved erosion surface

Plate interface rheological switches during subduction infancy: Control on slab penetration and metamorphic sole formation

Extension-parallel folding in the Scandinavian Caledonides: Implications for late-orogenic processes

A new geodynamic interpretation for the South Portuguese Zone (SW Iberia) and the Iberian Pyrite Belt genesis

Collapse basin: A new type of extensional sedimentary basin from the Devonian of Norway