Have you ever taken a drive in Oregon back roads and then found bizarre green rock outcrops? Most of Oregon roadside rock is layered sedimentary sand and silts or old cold layers of black lava or brighter covered rhyolites in south-eastern Oregon.
Below, Readers will be offered several key bizarre rocks to look for driving or walking in greenstone geology. The slide show will show each new type of rock totally foreign to most people. Greenstone region often are prehistoric “Subduction Zones.”
The Oregon coast has a subduction zone 40 miles off Newport (OR) and ancient subduction zones are marked typically with a serpentine green rock – it acts like geothermal-heated green toothpaste squeezed up into the cracked continental rocks basically by rising steam.
Sometimes stationary serpentine-based green minerals get baked into jade and other colorful gems by contact with molten granite deep underground at some later date; as our cover photo shows.
The cover photo shows green and blue Jade with very rare Biblical Hypersthene or “Bronzite” baked onto some typical Salt & Pepper Granite.
This real gem creation illustration comes from the Southfork of the John Day River above Dayville (Eastern Or) or the Aldrich Mountains. These odd green Aldrich Mountains were once prehistoric Pacific Ocean seafloor basalts. The proposed geologic process that brought these 100 million year old, seawater basalts to the top of the Continent is called “Subduction”?
Here is an interesting place for more information later:
“The Earth is like a birthday cake — layered and containing prizes.
Virginia Tech researchers are looking at the rock record from the last 600 million years to study the history of climate change and to determine where oil and gas may be hidden.”
Essentially a “subduction zone” is exactly where the floating or thicker North American Continental Plate (NACP) (slowly moving west) continually slides westerly at millimeters a decade over the Pacific Ocean’s huge, basic, basalt seafloor bottom Pacific Plate here in Oregon. Japan is getting closer to Oregon; but don’t hold your breath in anticipation of seeing Japan off our coast someday soon.
Obviously the two solid grinding rock Plates underground create the friction or heat that break, crack and churn solid rock in this process of subduction or “something going under something else”.
Moreover, like a tire on pavement, NACP tire friction kicks back a lot of loose debris under the tire moving it under the protruding tip or lip of NACP. This geologic rarity creates a warm stationary or rising Baking Pool or pond of seawater and Bizarre minerals mixing.
This greenstone geology is so rare; scientists are just starting to map and comprehend the “Green Stone Regions” world-wide.
I have added a fun video called the “Ecologies Presentation” to explain more about our Earth’s Continental Land Mass geology rolling over continually.
In a nut shell, the classic coastal “subduction zone” is one way our Oregon rocks get so delightfully jumbled and green or blue and this process can create very hard gemstones from Bluestones and Bronzite, Diamonds to Jade, Moonstone to Topaz.
Ironically, the Oregon coast was near Boise Idaho around 100 million years ago and that subduction zone the author studies to comprehend the very complex nature of “Metamorphic rocks” found in these rare geologically-trashed zones; as Oregon obviously does not have many metamorphic rock spots. These rare ancient rock spots are a messed up mélange of colorful greenstone and very hard bluestone (like at Stonehenge, England) and super baked gems and jewels.
We see mostly ancient Igneous or volcanic cold lava flows and geothermal hot springs or Sedimentary gravels & sandstone or muddy water heading to the ocean to become mudstone or buried shale.
When the author was a wilderness ranger in central Idaho walking around in early 1970s, he learned the local rock was the massive Idaho Batholith’s typical, salt & pepper Granite and occasional granite with large pink feldspar crystals. Oddly one can find this same “Salt & Pepper Granite” stone in the river gravels underlain Dayville or Eastern Oregon? Apparently there was once a huge river draining out of Idaho’s highland into the ocean that once covered eastern Oregon.
Oregon has abundant lavaflows around; and Idaho’s core mountains are made of volcanic lava that never reached the cooling air – Granite is lava slowly cooled into crystal.
Granite also is what often bakes the ancient rocks to create Jade; as the cover photo shows.
Where is Oregon Greenstone Deposit surfacing?
According to the U.S. Geologic Service study; Oregon has these greenstone spots to check out on West side and East side:
Condrey Mountain Schist (Triassic? and Paleozoic?) (Paleozoic(?) to Jurassic)
Consists of a variety of schistose rocks characterized by different proportions of muscovite, quartz, graphite, chlorite, actinolite, and epidote, rare thin layers of metachert, and clinozoisite-actinolite-albite-garnet metagabbro. Potassium-argon age on muscovite from unit is about 141 Ma (Lanphere and others, 1968) and on a whole rock sample is about 155 Ma (Suppe and Armstrong, 1972), indicating a Late Jurassic metamorphic age. Protolith (Original Land mass) is probably Triassic and Paleozoic in age.
Note: Ma means Millions of years ago!
Highly sheared graywacke, mudstone, siltstone, and shale with lenses and pods of sheared greenstone, limestone, chert, blueschist, and serpentine. Identified as melange by some investigators
Sedimentary and volcanic rocks, partly metamorphosed (Triassic and Permian) (Permian to Triassic)
Complexly folded, locally highly foliated and recrystallized undifferentiated sedimentary and volcanic rocks that in places are lithologically similar to Jurassic and Triassic rocks in the Aldrich Mountains of the Blue Mountains province and in other places …
Now let us figure out how Aldrich Mountain’s Melange left clues for all Oregonians to use to figure out the other drive through greenstone deposits all around the state.
Remember a subduction zone is a process the uplifts the ancient sea floor basalts that does not happen very often.
Here are three rocks types that show a subduction zone happened here; as I find these above Dayville along the Southfork of the John Day River.
First seawater mixes with rising basalt to create “Spilite” or an odd, bubbly old basalt filled with white Zeolites that obviously documents heated geothermal seawater filters through the ocean floor basalt that pillow-up or bloat up with steam upon contacting cold sea water. Odd “SPILITE” WILL BE IN THE SLIDE SHOW!
Readers an internet search by names will offer more in-depth Green stone details. For example “Lawsonite” is not pictured; but very common in Subduction zones.
Anyway, this basically hyper-heated steam can float the altered basalt of serpentine & hot air can bring the green melange up to the surface; as we call it a greenstone area.
Ophilites structures are too complex to explain here adequately really; so let us move on to viewing the slide show to simply see how Oregon Gems are created!
You will all find these gems in gravels in streams & drainages in these greenstone areas!
The State of Oregon & Idaho owns the watershed or gravels in streams and they allow someone to collect gravel free of charge. Use of a shovel and shaker and bucket can collect a lot of nice jewelry stone in an hour?
Enjoy your outdoors; as you respect Nature and revere it!
Reader please subscribe for free to gain another insight into Oregon’s wonders or plan your next field outing or adventure. There are over 250 Oregon wonders described in this Database created since January 2010.
Dave writes nonfiction books for sale on Amazon and Ebooks too!
UWA EART3343 Structural Geology & Tectonics: Eclogue Presentation