Thunder egg

I can start a new topic if needed.

One place was:
forum.rocktumblinghobby.com/post/748167/thread

Richardson Ranch is on part of the John Day Formation.

At "the ranch," as the hot water turned to steam, the spheroids tended to break into more or less internal six sided box shapes.


Basics are that Si-O² structures change with temperature and pressure. (AND the presence of other elements)

Heating up from Zero to 10,000, first the core of one element will increase vibrating to the point where the "Forbidden Zone" will increase to the point where the electrons are forced to move out to the next path; then the other will soon follow suit. this increases their sizes

- Quantum Mechanics -.

This is a predictable and repeatable path, occurring at precise temperatures and pressures.

Increasing from room temperature: SiO² gel > opal > needles > spheroids > chalcedony > moganite > alpha quartz > beta quartz > 7 forms of tridymite > 2 forms of cristobalite > spheroids > liquid > gas > plasma.

Cooling Down is a different matter.



Most volcanoes are subduction volcanoes with a life span of only several thousand years. Not time enough to grow very large spheroids.

Spheroids in Utah obsidian.

HOT-SPOT VOLCANOES are a very different matter! They live for many millions of years. The longer they go between eruptions, the more time to add new layers to each spheroid, adding to ever larger spheroid and ultimate thunderegg size at that location.

Siletzia Large Thundereggs are found all along it's track.

60 Ma the Siletz hotspot suddenly appeared off the west coast of America. From a depth of perhaps 200 - 600 miles superheated mantle material began welling up, spewing basalt that became the huge Siletzia Seamount.
For the next 10 ma Siletzia became massive, around 10,000 cubic miles of basalt - about the size of Hawaii!!

This crashed into the Washington/Oregon coast ~50 Ma. As the hotspot moved under the continent, it began melting and spewing limestone from the continental shelf, then as the continent moved over it, silica rocks. (I think it was an extremely high speed - perhaps 1/8th the speed of light from a nearby supernova ? - asteroid impact)

From Siletzia to Yellowstone

Age Name State Volume
57-50 Ma Siletzia Oregon 10,000 Cu. Mi.
54-39 Ma Tillamook Oregon
41-25 Ma Wildcat Mt. Oregon
29 Ma Smith Rock Oregon

13-10 Ma Crooked River Oregon
16-15.1 Ma McDermitt Oregon/Idaho
13.8-12 Ma Oyhee-Humbolt Oregon/Idaho
12.5-11.3 Ma Bruneau-Jarbidge Oregon/Idaho
10-8.6 Ma Twin Falls Idaho
10.2 Ma Picabo Idaho
7 Ma Rattlesnake Tuff Oregon
6.6-4.4 Ma Heise Idaho
2-0.6 Ma Yellowstone Idaho.Wyoning

The original Siletzia basalts are tholeiitic, a characteristic of mantle-derived magma erupted from a spreading ridge between plates of oceanic crust. The younger basalts are alkalic or calc-alkaline, characteristic of magmas derived from a subduction zone. This change of composition reflects a change from marine to continental volcanism that becomes evident around 48 to 42 Ma (millions of years ago), and is attributed to the accretion of Siletzia to the North American continent.


OREGON
1. Siletzia Washington/Oregon - (58-50 Ma) - tholeiitic basalts turn to alkalic or calc-alkaline basalts.

2. Tillamoock Oregon Caldera - (54 to 39 Ma) - calc-alkaline basalts turn to silicates.

The older Clarno Formation consists of Eocene non-marine alkaline to calk-alkaline volcanic rocks and intrusions and volcanogenic sedimentary rocks that reputedly range in age from ca. 54 to 39 Ma

3. Wildcat Mt. Caldera - (41-25 Ma) - John Day Formation - first Thundereggs - Madras, Richardson Ranch, Lucky Strike Mine

Robinson and Brem (1981) divided the John Day Formation into a “western”, “southern”, and “eastern” facies (Figure 1). The “western” facies is divided into members designated alphabetically from A to I (Figure 4; Peck, 1964; Robinson and Brem, 1981; Robinson and others, 1990). The “eastern” facies is divided into four members that include from oldest to youngest the Big Basin, Turtle Cove, Kimberly, and Haystack Valley members (Fisher and Rensberger, 1972). The “southern” facies has not been formally divided into members. The base of the John Day Formation is generally defined by the regionally widespread Member A ash-flow tuff that has 40Ar/39Ar ages of 39.72 ± 0.03 Ma near the Painted Hills, 39.22 ± 0.03 Ma near Clarno, and 39.17 ± 0.15 Ma near Ashwood (Bestland and Retallack, 1994a,b; Smith and others, 1998; Retallack and others, 2000). An ash flow defined as Member I near the top of the formation has been dated at 27.7 ± 0.3 Ma (K/Ar) but may be as young as 22 Ma

Mercury from the impact began reaching the surface in the 39 Ma eruptions.
Intermediate to silicic basement rocks and rocks associated with the Wildcat Mountain caldera are characterized by relatively enriched amounts of Al (aluminum) and corresponding relatively depleted contents of K (potassium), Na (sodium), and Fe (iron). These rocks also display characteristically low contents of incompatible high-field-strength elements (HFSE) such as Nb (niobium) and Zr (zirconium), low contents of Y (yttrium), and, generally, lower abundances of the light rare-earth elements (LREE) La (lanthanum) and Ce (cerium)

Oligocene Crooked River caldera
10–13 Ma younger Lower Crooked volcanic field rocks. Mafic rocks preserved within the Lower Crooked volcanic field are Fe- and Ti-rich tholeiites while silicic rocks are characterized by relatively enriched amounts of Y, Zr, Nb, La, and Ce

?. Smith Rock Caldera, Bend Oregon - 29 Ma
The geology of Smith Rocks is volcanic. It is made up of layers of recent basalt flows overlaying older Clarno ash and tuff formations. Approximately 30 million years ago, a large caldera was formed when overlying rock collapsed into an underground lava chamber. This created a huge amount of rock and ash debris that filled the caldera. That material solidified into rock, becoming Smith Rock tuff. Rhyolite flows intruded along faults in the Smith Rock Tuff. [2] A half million years ago, basalt lava flows from nearby volcanoes covered the older tuff.[3][4][5]

More recently, the Crooked River cut its way through the layers of rock to create today's geographic features. Smith Rock itself is a 3,200-foot (980 m)-high ridge (above sea level) with a sheer cliff-face overlooking a bend in the Crooked River (elev. 2600 ft), making the cliffs about 600 feet high.

Tower Mountain Caldera


OREGON/NEVADA
McDermitt Caldera (16-15.1 Ma)

OREGON/NEVADA/IDAHO
Owyhee-Humboldt Caldera (13.8-12 Ma)

NEVADA/IDAHO
Bruneau-Jarbidge Caldera (12.5-11.3 Ma) Bruneau Thundereggs

IDAHO
Twin Falls Caldera (10-8.6 Ma)
Picabo Caldera (10.2 Ma)
Heise Caldera (6.6-4.4 Ma) V

IDAHO/MONTANA/WYOMING
Yellowstone Caldera (2-0.6 Ma)

The LARGEST Spheroids I know of are at Silver Cliff Colorado, near NRG Scott Solar's new home.

Nice TE's...... RR's are my favorite..