Erickson, Rolfe
http://hdl.handle.net/10211.1/333
2024-03-28T10:00:03ZGiant Intrusive Volcanic Breccia Complex in the Dos Cabezas Mountains, Arizona
http://hdl.handle.net/10211.3/199309
Giant Intrusive Volcanic Breccia Complex in the Dos Cabezas Mountains, Arizona
Erickson, Rolfe
The Dos Cabezas mountains are a medium-sized range outcropping in southeastern Arizona near the town of Willcox. They are dominantly a Precambrian complex composed of 10 granitoid plutons and 3 multi-km² terranes of Pinal Schist and Bear Canyon Series. (Erickson, 1969 and 1993). This Precambrian complex is overlain by two deformed Mesozoic ignimbrites, and all these older-units are intruded by several Mesozoic plutons and mid-Tertiary dikes. The oldest ignimbrite is 67 Ma; I judge this is the approximate age of the slightly younger breccia system as well. Paleozoic and Mesozoic sedimentary units typical of southeast Arizona are also found (Erickson, 1969). All these units are cut by strands of the regional WNW striking Apache Pass fault system. These preexistent units are cut by innumerable irregularly shaped intrusive breccia bodies with sizes ranging from small 1-5 m dikes and pods to bodies many kilometers across. These are roughly classified here by matrix color into green, purple, and white groups. The green breccias are by far the most abundant of these. In their post-Precambrian development, active faults forming in the Apache Pass tectonic system extended into the center of the Dos Cabezas range, where, I hypothesize they outlined blocks of crust up to several kilometers across. These blocks became partly or wholly detached from their walls and they sank into the fluidized main green breccia body. The largest green breccia body contains four giant blocks of wall units up to 3 km in maximum dimension, wholly detached from their original location and probably sunk from their original level; these are each partly surrounded by fields of blocks in breccia matrix grading down from multi-kilometer size to hand specimen size and then down to dust. I call such areas block fields. The intrusive contacts of the breccia bodies with their wall units have ~ 1 km of relief, and are commonly well exposed. The breccia bodies were intruded into their walls and roofs as masses of fluidized fragments transported upwards by gases rising vigorously from deeper-seated magma. The giant blocks in the breccia complex were sinking in the fluidized beds when fluidization ceased, in the same manner as similar giant blocks in kimberlite breccia pipes in Africa (McCallum, 1985). There are no surficial breccia eruptive units preserved in the breccia complex (Shawe and Snyder, 1988 and Shawe, 1985). The green breccia alone has been autometamorphosed under hornblende-hornfels facies conditions; abundant metamorphic epidote colors it green. Presence of a ~ 1 km² exposure of typical green breccia in the Circle Hills (Erickson, 1988), 20 km west of the Dos Cabezas mountains, suggests the breccia terrain may be much more widely distributed than can presently be demonstrated.
2017-01-01T00:00:00ZPetrology of a Franciscan Olistostrome with a Massive Sandstone Matrix: The King Ridge Road Melange at Cazadero, California
http://hdl.handle.net/10211.3/158143
Petrology of a Franciscan Olistostrome with a Massive Sandstone Matrix: The King Ridge Road Melange at Cazadero, California
Erickson, Rolfe
The King Ridge Road melange is a unit of the Franciscan Complex, cropping out
in an area of at least SO km2 around the town of Cazadero, coastal California. This
unit is an olistostrome with a massive, unfoliated sandstone matrix, containing >232
large meta-igneous and chert blocks of greatly varying size, lithology, and metamorphic
history within the study area. This sandstone matrix is litharenite or arkosic
arenite and exhibits prograde prehnite-pumpellyite facies and retrograde zeolite
facies metamorphism. It is devoid of megascopic textures except for rare simple bedding.
No fossils have been found, and no Bouma units or other graded beds are present.
Detrital zircon geochronology has established the maximum age of deposition of
the sandstone matrix at 83 Ma, whereas apatite fission-track data indicate cooling
of the olistostrome below 100 °C at ca. 35-38 Ma. The 232 exotic blocks sampled in
the study area are dominantly low- to medium-grade greenstones and cherts, together
with fewer high-grade blocks partly composed of blue amphibole and/or omphacitic
pyroxene, and some amphibolites. Thus, many of the blocks have higher grade metamorphic
assemblages than the matrix. All block types are well mixed together, so none
greatly predominate anywhere. Blocks of oceanic-island-arc platonic rocks, including
granitoids and recemented breccias, are particularly distinctive for this melange. One
granitoid block has a zircon U-Pb age of 165 ± 1 Ma. The massive sandy matrix of
the olistostrome formed by accumulation of hyperconcentrated sedimentary density
flows (grain flows) sourced primarily from the Klamath-Sierra continental magmatic
arc. Many of the blocks record a pre-melange history of metamorphism and exhumation,
followed by partial subduction and reburial with the matrix after 83 Ma. Cooling
below 100 °C took place at 35-38 Ma, probably associated with partial exhumation
of the unit, with subsequent removal of -10 km of cover.
2011-01-01T00:00:00ZProducing an Accurate Crystal Drawing in Any Orientation from a Stereogram
http://hdl.handle.net/10211.3/158129
Producing an Accurate Crystal Drawing in Any Orientation from a Stereogram
Erickson, Rolfe
A wholly general method is presented to produce
accurate drawings of any crystal in any orientation
from a stereogram of the crystal. A standard
stereogram is prepared with all faces plotted, and
the desired viewpoint is marked. The stereogram
is then rotated as necessary to place this mark on
the W radius of the net. The stereogram is then
held in position, and the viewpoint moved along
the W radius to the center of the net. Concurrently,
all face poles are moved along their small
circles by the same number of degrees and with
the same sense of motion as the viewpoint. The
poles are now reoriented.
Next, appropriate zone circles and their diameters
are drawn. Each zone has a zone pole whose direction
on the stereogram is parallel to the edges in
the zone. A line parallel to this zone pole, called an
edge line, is drawn from the net into the adjoining
drawing area. Edge lines are drawn for each zone
of the crystal, and the crystal drawing is then
made by drawing necessary edges to outline faces.
1998-01-01T00:00:00ZHow to Make an Accurate Three-Dimensional Model of Any Crystal from Its Stereogram
http://hdl.handle.net/10211.3/158128
How to Make an Accurate Three-Dimensional Model of Any Crystal from Its Stereogram
Erickson, Rolfe; Barthelmy, Lance Gerald
To make an accurate three-dimensional model
of any crystal, plot partial stereograms of one face
from each form on the crystal and all the faces
with which it shares edges. Rotate each partial
stereogram until the chosen pole is on the W radius
of the stereonet. Translate the desired pole
to the east along the W radius to the center of the
net, moving all other poles congruently along the
small circles of the stereonet. Label the reoriented
poles. For any edge, draw a zone circle containing
the poles of the chosen face and its edge neighbor,
and the zone pole line. The orientation of this
zone pole line is also that of the common edge of
the two faces, so an edge orientation line may be
drawn parallel to it. Then, draw this edge line on
the stereogram at a convenient position and repeat
for all edges of the face. Next, arrange the
edges to make a face of chosen shape and size and
repeat for all faces, keeping common edges constant
in length. Finally, transfer multiple copies
of each face drawing to a rigid material such as
sheet balsa, cut them out, and glue the faces together
with wood glue to make the model.
2000-01-01T00:00:00Z