2002 Abstracts
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January 2002
"SHOULD WE BE CONCERNED ABOUT EARTHQUAKES IN COLORADO?"
Vince Matthews
Colorado Geological Survey
In general, Colorado is not considered to be at risk from significant earthquake damage. The state is
ranked 30th in the nation in terms of Annualized Earthquake Losses by the Federal Emergency Management
Agency and Denver is rated by the USGS National Seismic Hazard maps as having about the same seismic
risk as Atlanta, Georgia. However, a growing body of data suggests that Colorado may be at greater
risk than previously recognized. Colorado has the second largest heat flow anomaly in the North
American continent, fifty-nine peaks over 14,000 feet in elevation, and extensive Neogene deformation
indicating an active tectonic province. The catalog of Quaternary faults has steadily increased from
none in 1960 to nearly ninety in 1998 with many areas of the state unexamined. The large 1882
earthquake has been definitively located in the northern Front Range. Studies of Quaternary faults
in Colorado have resulted in thirteen faults being assigned a "maximum credible earthquake" >Mw 6.25
and as high as Mw 7.5. With Colorado's rapidly growing population (3rd fastest in the nation)
significant, additional research needs to be directed toward Colorado's earthquake hazard.
"A TRAVERSE IN TIBET: CULTURES AND CONTINENTS IN COLLISION."
Bob Raynolds
Consulting Geologist, Longmont, CO
The dramatic effects of plate tectonics have given us the topographic features of the Himalayan mountain front and the
Tibetan plateau. Huge thrust faults carry delaminated continental crust and associated passive margin sediments up
and southwards across the northern fringe of India. The suture zone marking the vanished Tethys Seaway is defined
by ophiolites and deep-sea trench sediments that now lie exposed to the sun on the Tibetan Plateau. Confrontations of
similar magnitude exist between cultures in Asia and Western life-styles, contrasting worlds brought increasingly into
contact by the efficiency of communication and ease of travel. This talk will examine some of the manifestations of both
styles of collision. The future behavior of the plates may be the easier of the two outcomes to predict.
February 2002 - Emmons Lecture
"TRANSTENSION IN ARCS AND OROGENS"
John F. Dewey
Department of Geology, Uuniversity of California at Davis
Transtension is oblique extension, a combination of coaxial zone-orthogonal extension and
non-coaxial zone-parallel shear. It is typical of extensional zones for many reasons, mainly
because plate boundary and deformation zones are rarely perfectly orthogonal to plate and
block boundaries. The transport direction (TD) is defined as the slip vector between the
separating blocks or plates. The instantaneous extension direction (Xi) is not parallel with
TD but bisects the angle between TD and the zone boundary orthogonal. The finite
extension direction (X) rotates towards TD. Lines, planes, and structures in the obtuse
angle between TD and the zone orthogonal rotate, with vorticity, towards TD; those in the
acute angle rotate against vorticity towards TD. Where the angle (a ) between TD and the
zone orthogonal is less than 70.5º, the principle shortening direction (Zi) is vertical and the
intermediate (shortening) direction (Yi) is horizontal. This generates sub-horizontal foliation
and vertical dykes and fissures and steeply dipping conjugate normal faults intersecting in
Yi and folds and constrictional stretching lineations parallel with X. Where a is greater than
70.5º, Zi is horizontal and Yi is vertical, generating vertical foliation and conjugate
strike-slip faults (Riedels and anti-Riedels) an folds and lineations prallel with X. Thus, TD
can be calculated for any deformation zone where the angle a /2 can be determined; this is
of enormous potential in determining relative plate motions.
Transtension is of great importance but is, as yet, very poorly understood in convergent
plate boundary zones. Intra-oceanic juvenile arcs are dominated by transtension where
subduction rollback occurs with motion of the over-riding plate away from the trench line. In
Newfoundland, a fine example of a transtensionally-distended Cambria-Ordovician arc
with oblique dykes and horizontally stretched pillows and supra-subduction-zone ophiolites
is superbly exposed with a complicated polyphase structural and igneous history.
Transtension dominated the late extensional "collapse" of several orogens. Orogenic
transtension leads to tectonic denudation by crustal thinning and extensional detachment
and the development of high temperature/and low-pressure metamorphic assemblages
with subhorizontal foliations and stretching directions, so typical of the Tasman Belt of
Australia and the Variscan belt of Europe. Transtensional Xi and X parallel folds are
expressed as periclines and "corrugations" in extensional detachments in the Cenozoic
Basin and Range and in the Silurian Caledonides of western Norway.
March 2002
"TERROIR - THE CONNECTION BETWEEN WINE AND GEOLOGY"
Larry Meinert
Department of Geology, Washington State University, Pullman, WA,
Meinert@wsu.edu
Terroir is a relatively simple term to describe the complex interplay of climate, soil, geology, and other
physical factors that influence the character and quality of wine. Although the term has long been used
in France, it is increasingly being used in other parts of the world to try to better understand the cause
and effect of great wine. This talk will focus on the terroir of Washington State, which is second only
to California in terms of wine produced in the United States. This is somewhat surprising in that
Washington has a relatively short history of wine production by international standards. Although the
first Vitis vinifera grapes were planted in 1825 by the Hudson's Bay Company along the banks of the
Columbia River in southwest Washington, commercial production extends back only about 100 years
and most of the state's 155+ wineries were started in the past 15 years (there were only 19 wineries
when the author moved to Washington in 1981).
Washington is a region of superlatives, both oenological and geological, with exposures of some
of the world's largest and most spectacular flood basalts, dune and loess fields, and glacial outburst
flood deposits. All of these play a part in the terroirs of Washington State wines. In addition, recent
volcanic activity such as the well-known 1980 eruption of Mt. St. Helens continues to shape the
oenological and geological landscape. Most Washington State vineyards are located between latitudes
45° and 48° N, well to the north of the more widely known California vineyards but parallel to some of
the great French wine regions such as Burgundy and Bordeaux. This northerly latitude provides about
two hours more summer sunlight than occurs in California wine regions. In addition, most Washington
vineyards lie in the rain shadow of the Cascade volcanic arc, and many vineyard soils have a compo-nent
of ash from Mt. St. Helens and other Cascade volcanic eruptions such as the much larger Mt.
Mazama eruption (6,850 yr BP) which formed present day Crater Lake in Oregon.
Although there is considerable local variability, most Washington vineyards are located on
Quaternary sediments and soils that overlie Miocene basaltic rocks of the Columbia River flood basalt
province. Many of the Quaternary sediments are related to cataclysmic glacial outburst floods that
formed the spectacular geomorphic features of the Channeled Scablands. This in itself is one of the
great geologic stories of all time, and the fact that it is intimately related to superlative wine makes a
discussion of Washington wine and terroir particularly worthwhile. The fact that some of the geological
and soil features are unique to this part of the world suggests the possibility that Washington wines
(including Cabernet Sauvignon, Chardonnay, Merlot, Riesling, and Syrah) may develop flavour and
quality characteristics that set them apart from other wine-producing areas.
April 2002 - Annual Family Night
"GEOLOGY GOES HOLLYWOOD AND OTHER PUBLIC PERCEPTIONS OF GEOSCIENCE"
Sarah Andrews
Sonoma State University, Sonoma, California
If the way geology is portrayed in such cultural vehicles as Dante’s Peak (remember that SUV
sashaying across hot lava?) and Star Trek (how did the cave floors of all those unexplored planets get so
flat?) is any indication, America is either scientifically ignorant or has a rich vein of wry humor. While
I hope it’s the latter, some of the reviews my books get suggest that it’s the former. It’s enough to make
me want to found a geology anti-defamation league.
The media appear to be here to stay, so I suggest instead that we bend it to our will. Geologists
are natural storytellers, and telling stories is the media’s stock in trade. The human species is just as
easily entertained, and are better informed, by reality-based stories as by fantasy. Certainly the public’s
interest in the geology snaps to attention each time the earth shakes, spews molten rock, or disappears
under water. And many people evidence an authentic longing to know more about the oblate spheroid
they live on. How many of us have heard phrases like, “I’ve always had a secret desire to [be a
geologist] [know more about geology] [study dinosaurs], but [I knew I couldn’t do the math] [my
parents wanted me to study dentistry instead] [I was born female in the wrong generation], so…”
Visual, auditory, and literary storytelling is as powerful a tool for influencing public opinion as
it ever was. The media consciously and unconsciously sell not only reality and fantasy, but also
cultural values and valuation. The stories people hear strongly influence their political, ethical,
religious, and scientific beliefs. It is important therefore that we understand and fully utilize this tool,
and emerge not only as sympathetic protagonists rather than flat, passionless, often ominous antagonists
in someone else’s story, but also as authors of an advancing culture.
Sarah Andrews is the author of seven forensic geology mystery novels and is a lecturer in
Geology at Sonoma State University. She holds a B.A. from Colorado College and an M.S. from
Colorado State University and is the recipient of the 1999 AAPG Journalism Award and the 1997
RMAG Journalism Award.
The hilarious and thought-provoking video “Geology Goes Hollywood,” produced by Dr.
Dorothy Stout and edited by Deborah Steller, will be shown for the second part of this media-oriented
family-night program.
May 2002
"OVERVIEW OF CIVILIAN SATELLITE IMAGING SYSTEMS - HOW IT IS REVOLUTIONIZING WORLDWIDE MINERAL EXPLORATION"
Sandra L. Perry
Perry Remote Sensing LLC, Englewood, Colorado
Civilian imaging satellites have been in orbit since 1972 and have provided a valuable database for a
variety of earth science applications. Digital image analysis of these satellite data systems has aided
vegetation mapping and monitoring, mineral & hydrocarbon exploration, agricultural uses and planning,
archeology, and global change observations. From a mineral exploration standpoint, image analysis has
provided timely, ready-to-go information that offers both geological and logistics information for
worldwide operations. In the last three years, new satellite systems have revolutionized how mineral
explorationists and field geologists conduct international exploration. These new systems offer higher
spectral and spatial resolution detail, which coupled with global positioning systems (GPS) and geographic
information systems (GIS) makes fieldwork more effective and efficient. With more demanding needs for
metals worldwide, satellite imagery together with GPS and GIS have become necessary tools for the field
geologist. This presentation will summarize applications of satellite imagery for international mineral
exploration and field geology.
"THE USOI LANDSLIDE DAM AND LAKE SAREZ, SOUTHEASTERN TAJIKISTAN"
Robert L. Schuster
U.S. Geological Survey, Golden, Colorado
In 1911, a massive earthquake-triggered rock slide (volume: ~2 km3) dammed the Murgab River in the
Pamir Range of southeastern Tajikistan. The still-existing blockage is 600 m high, by far the largest
dam, natural or man-made, in the world. Lake Sarez, impounded by this natural dam, is about 60 km
long, with a maximum depth of approximately 550 m, and a volume of about 17 km3. The lake has never
overtopped the dam; instead, it exits the downstream face as several large springs that regroup to
form the Murgab River. There currently is about 50 m of freeboard between the lake surface and the
lowest point of the dam crest, and the lake is rising at about 20 cm/yr.
If this natural dam were to fail, a worst-case scenario would endanger some five million people in the
Bartang, Panj, and Amu Darya valleys downstream. Dam failure potentially could be due to: (1) seismic
shaking, (2) catastrophic overtopping caused by a landslide entering the lake at high velocity from the
valley wall, (3) surface erosion due to natural overtopping by the slowly rising lake, (4) internal
erosion (piping), (5) instability caused by pressure of the lake against the dam, or (6) instability
of the slopes that form the dam faces. Because of the high cost of installing physical remediation to
the dam in this rugged mountain area (there are no roads to the dam), the main protective measures now
being undertaken are hydrological monitoring at the dam and installation of a flood early-warning system
downstream.
Recent studies of the Usoi landslide and natural dam and Lake Sarez, which have been funded mostly by
the World Bank, the Swiss government, the Government of Tajikistan, and USAID, with cooperation from
FOCUS Humanitarian Assistance, have been carried out mainly by Stucky Consulting Engineers of Lausanne,
Switzerland. Field studies currently are “on hold” because of the situation in Afghanistan, but Stucky
engineers and geologists currently are planning to return to the field in May of 2002.
September 2002
"THE USGS NATIONAL WATER QUALITY ASSESSMENT PROGRAM AND WATER QUALITY IN THE UPPER COLORADO RIVER BASIN"
Norm E. Spahry
USGS National Water Quality Assessment
Streams and rivers in the Upper Colorado River Basin (UCOL) are very different in the two major physiographic
provinces. In general, streams within the Southern Rocky Mountains are characterized by lower sediment and
dissolved-solids concentrations, cooler temperatures, and somewhat higher gradients than streams in the
Colorado Plateau. Sediment, salinity, and nutrient (nitrogen and phosphorus) concentrations increase along
the major rivers as the water flows from the upstream areas in the Southern Rocky Mountains down through the
Colorado Plateau.
Coupled with the general differences due to physiography and geology are the effects of different land uses.
Recreation and urban development are becoming major land-use issues throughout the basin, precious metal mining
was historically prevalent in the Southern Rocky Mountains, and intensive agriculture is located in the valleys
of the Colorado Plateau.
Most of the streams and rivers sampled within the UCOL met State and Federal water-quality guidelines. Major
exceptions to this statement were trace-element concentrations in some streams in the Southern Rocky Mountains
and selenium concentrations in some streams in the Colorado Plateau. The talk will discuss other selected
findings regarding nutrient concentrations, algae, mining areas, pesticides, and herbicides.
"SAND DUNES ON THE GREAT PLAINS AND THEIR NOT-SO-ANCIENT HISTORY"
Daniel R. Muhs
U.S. Geological Survey, Denver, Colorado
Eolian (wind-blown) deposits, such as sand dunes, are both a blessing
and a curse: they contain a valuable record of past climate changes but are
deposits that could be reactivated in the future, with serious consequences
for the natural resources, food supply, infrastructure, and wildlife of the
country. In this talk, new geologic and historic records of eolian sands
of the U.S. Great Plains will be presented. In addition, I will assess the
potential for renewed activity of wind-blown sediments under possible
future drought conditions.
Sand dunes are extensive on the Great Plains. The Nebraska Sand Hills
region is the largest sand sea, active or stabilized, in North America.
Dunes also occur over large areas of eastern Colorado and New Mexico,
western Kansas, and the panhandles of Texas and Oklahoma. Modern winds on
the Great Plains are stronger than in most of the world's deserts.
However, sand dunes on the Great Plains are inactive at present because of
a sparse cover of grass and associated grassland community plants, such as
sage, yucca, and cactus.
Previously, it was thought that most sand dunes on the Great Plains
were last active during the last glacial period, at least 12,000 years ago.
New radiocarbon ages show that most dunes on the Great Plains have been
active in the past 3,000 years. In addition, accounts of early explorers
show that many dunes were active during the 19th century. Examination of
aerial photographs in the National Archives shows that some dunes, stable
now, were active during the 1930s "dust bowl" drought. Thus, it can no
longer be assumed that these dunes are ice-age features that have little
threat of reactivation in the future.
Great Plains dunes have been active, therefore, under interglacial
climatic conditions that are only slightly different from the present. If
the dunes are reactivated in the future, either from human-caused global
warming or natural climatic variation, there would be significant impacts
on the region. Stabilized dune fields at present form some of the most
important areas of grazing land. Areas immediately downwind of the dunes
are important croplands. Interstate highways and railroads are also
downwind of large dune fields. Many interdune areas, particularly in the
Nebraska and North Dakota, are wetlands that support wildlife. Thus,
reactivation of Great Plains dunes would have significant impacts on both
human society and wildlife of the region.
October 2002
"DETERMINING THE EFFECTS OF WASTEWATER POLLUTANTS ON THE DILLON RESERVOIR WATERSHED, COLORADO, USING A
WATERSHED-SCALE WATER QUALITY MODEL"
Paula Jo Lemonds
Department of Geology and Geological Engineering
Colorado School of Mines
With over 1,000 onsite wastewater systems (OWS) in the Dillon Reservoir watershed located in Summit
County, Colorado, the effects of effluent from these systems are important for watershed water quality
management. Thin soils hinder the attenuation of wastewater effluent and can allow nutrients to reach
groundwater resources or surface water bodies. The objective of this study is to quantify the influence
of OWS pollutants on the ground water and surface water using a watershed-scale water quality model.
The EPA’s Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) and the Soil and
Water Assessment Tool (SWAT), which is interfaced with BASINS 3.0, were applied to this problem. SWAT
utilizes physically based data, simulates land use and management scenarios, and takes into account
process interactions through a GIS environment. Water-quality data from groundwater and surface water
samples, as well as streamflow and groundwater hydraulic head measurements are being collected at three
focus areas in the watershed. Data collected upstream and downstream of each of these sites show a
change in the signature of nitrate and phosphorus, two wastewater constituents. This information is
used to evaluate the performance of the model, which uses national public-access databases for initial
model development.
"RE-OS DATES FOR THE MALANJKHAND DEPOSIT, AN ARCHEAN TO E. PROTEROZOIC PORPHYRY"
Aaron Zimmerman (presenter, undergraduate student), Stein, H., Hannah,
J., Markey, R., Sarkar, S.C., and Pal, A.B.
Colorado State University
The Malanjkhand Cu(Mo) ore deposit, a subduction related porphyry
located in Central India, is one of a handful of Archean to Early
Proterozoic porphyry deposits found worldwide. As a result, the age,
genesis, and classification of the deposit are highly debated in the
literature. The Re-Os geochronometer provides a means for quelling the
debate, and the analyses show a variety of well constrained dates
corresponding to multiple mineralization events.
The dates are derived from a series of samples corresponding to the
differing rock types seen at the site. The host rock is a potassically
altered and deformed granodiorite with disseminated molybdenite and iron
sulfides. The pluton is cut by planar, steeply dipping, quartz veins
containing stringers and blebs of sulfides including molybdenite and
chalcopyrite.
Based on 5 different molybdenite samples, the geologic history is
that the host granite was the first to be mineralized at 2493 ± 3 Ma.
At 2491 ± 8 Ma, small quartz veins are mineralized in small fractures in
the host granite. Large quartz dikes form next at ~2476 Ma and at ~2452
Ma. The entire history is well constrained by replicate analyses and
field relationships.
The dates show that the deposit is Archean to Early Proterozoic in
age and the Re concentrations are similar to those seen in younger
subduction-related porphyry systems. Only by using the Re-Os
geochronometer can highly precise dates distinguish the numerous
mineralization events that occurred at Malanjkhand.
"HYDROGEOLOGIC INVESTIGATION INTO THE EFFECTS OF MANAGED RECHARGE ON WATER QUALITY, LOWER SOUTH PLATTE
RIVER"
Jamey T. Watt (presenter, M.S. student), Sanford, William E, Stednick,
John, and Durnford, Deanna
Colorado State University
In order to meet in-stream flow requirements at the Colorado-Nebraska
border, managed recharge along the lower South Platte River Basin is
being used as a method for flow augmentation. The site is located on the
Colorado Division of Wildlife's Tamarack Ranch State Wildlife Area in
northeastern Colorado. During late winter/early spring, when there is no
call for water from the South Platte, approximately 20 acre-feet per day
of water is pumped from the alluvial aquifer near the river into a
recharge pond approximately 1 km away. The goal is to have water return
to the river during low flow periods prior to snow melt runoff in order
to augment in-stream flows for endangered species in Nebraska. In this
talk, we will present current findings on the areal and temporal
distribution of water quality parameters (including nitrate, sulfate,
alkalinity, DO, and specific conductance) within the alluvial aquifer
between the recharge pond and the South Platte River. Data collected to
date suggest 1) a zone of higher nitrate levels along the alluvial
aquifer nearer the river; 2) the sulfate concentrations of the water
pumped into the recharge pond is similar to that of the alluvial aquifer
than to the river water; and 3) there appears to be a smaller
contribution from the river during pumping than initially expected. In
addition, we will present the preliminary results of a tracer test
performed to address recharge pathways and timing. The understanding of
the pathways and flow rates is important in determining the influence of
the recharge water on groundwater and surface water quality, especially
in light of the increasing use of flow augmentation along the length of
the lower South Platte River.
November 2002
"JONAH AND PINEDALE FIELDS, GREEN RIVER BASIN, WYOMING CASE STUDY OF TWO EMERGING GIANT GAS FIELDS"
John Robinson
Consultant
The Jonah-Pinedale area has undergone a renaissance in the last decade to become one of the fastest growing
producing trends in the Rocky Mountain region. Combined production from both fields is rapidly expanding and
pipeline capacity will be hard pressed to keep up with future production growth.
Jonah Field was discovered in 1986, but due to market conditions and ineffective stimulation methods, the
production was not economic. In 1992, McMurry Oil Company bought the field and invoked new drilling and
completion technology that unlocked the full potential of the play. The acquisition of 3D seismic resulted
in a revolutionary new image of the subsurface, including the existence of the Western Bounding Fault and
the Southern Boundary Fault that form the boundary of the pressure compartment. In the last few years, Jonah
Field has become the largest gas producing field in the Rockies.
The first drilling activity in the Pinedale area was in 1939. In 1971 the area became widely recognized as
a proposed site of an experimental subsurface nuclear stimulation, but the event never occurred. The field
was dormant until the successful application of similar drilling and completion techniques in nearby Jonah
Field revitalized the area. Recent acquisition of 3D seismic over the anticline has generated an improved
image of the feature and will allow optimization of development drilling. Estimates vary, but up to 500
wells may be drilled on the anticline when it is fully developed.
"SECRETS OF SULFURIC ACID CAVES"
Harvey DuChene
Miller, Dyer, & Co.
Many caves in the Guadalupe Mountains of New Mexico and west Texas contain sulfates, clays and other
minerals that are byproducts of the dissolution of limestone by sulfuric acid. Guadalupe caves such
as Carlsbad Cavern and Lechuguilla Cave also contain enigmatic mineral formations with shapes that suggest
that they were formed by, or nucleated around, filamentous or colonial bacteria. However, the processes
that formed Guadalupe caves ceased about 4 Ma, and the characteristics of these possible life forms are
unknown. To test the hypotheses that life existed in these caves while they were forming, several modern
sulfur caves were studied. These include the Kane Caves of Wyoming, Cueva de Villa Luz in Mexico, the
Frasassi Caves of central Italy, and Movile Cave in Romania. These caves are being formed today by the
action of sulfuric acid on limestone. In addition, they support a remarkable abundance of life forms,
including microbes that thrive in total darkness in low-pH environments and in an atmosphere filled with
toxic gases. The life forms in these extreme environments attracted the attention of scientists who see
them as possible analogs for life elsewhere in the universe.
December 2002 - Presidental Address
"A GEOLOGICAL EXCURSION IN NEW ZEALAND: COLLISIONAL SHORTENING AND DRAINAGE DIVIDE MIGRATION IN THE
SOUTHERN ALPS"
Eric Nelson
Colorado School of Mines
New Zealand is a geologically fascinating and beautifully scenic land that is not only tectonically very
active, but also serves to illustrate many of the geological processes involved in mountain building. In
2000-2001 I was fortunate to spend a sabbatical year on South Island and to study some of these
processes. I will report on the general tectonics of New Zealand and will focus on river piracy that has
resulted from crustal shortening adjacent to an active plate boundary. New Zealand started its rock life
as part of Gondwanaland, snuggled up against Australia and Antarctica. Cretaceous rifting relieved it of
this burden and produced a passive continental margin on the east coast that has been somewhat creaky
ever since; 20-10 million year old volcanoes are still exposed along this coast. Subsequently, New
Zealand took the form of microplates which jostled about and finally slid past one another as New
Zealand evolved from being home to a transform plate boundary to an oblique collisional plate
boundary, the Alpine fault. As along the San Andreas plate boundary in California, strain is distributed
for at least 220 km into the plate and is expressed as faults and folds. The Alpine fault transitions into a
diffuse southwest-vergent subduction zone to the south (Puysegur trench), and it splays to the northeast
into a broad zone of oblique wrench faults before changing to a northeast-vergent subduction zone
(Hikurangi trough) along the east coast of North Island. North Island today contains an extensional back
arc region with beautiful stratovolcanoes and geothermal springs known to be modern, active
mineralizing systems.
The Alpine fault is an obliquely convergent plate boundary and shows ~480 km of dextral offset and up
to 25 km of vertical separation since the Miocene. The convergent component is illustrated by the 4 km-high
Mt. Cook, and by impressive exposures of mylonitic garnet amphibolite thrust over Recent gravels.
The Main Divide region of the Southern Alps is being progressively shortened in response to the
convergent component of plate motion, and the rocks of the Main Divide region are being transported
westwards towards the plate boundary. This lateral migration of the continental divide has resulted in a
jog in the otherwise linear divide,
and in the capture of south-flowing
streams, which became
west-flowing streams. The region
of the divide jog was localized in
a zone of cross faulting, along
which hydrothermal fluid flow
concentrated, forming quartz-carbonate-(±
Au) veins. These
and other vein systems in the
Southern Alps show that
metamorphic dewatering in an
evolving orogen contributes to the
precious-metal budget of such
tectonic regimes, including some
of the Au placers to the east.
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