Strange formation on Colorado Rockies sheds lite on Earth’s past

Central Colorado’s Tava sandstone (light-colored band of stone at center, amongst geology educatee for scale) likely formed betwixt 680 1000000 together with 800 1000000 years ago, a novel study suggests.

Many outcrops of the “Tava sandstone”—derived from a Native American advert for Pikes Peak, a local landmark—are constitute along the Ute Pass fault, which runs along the Front Range nigh Colorado Springs. First noted yesteryear geologists to a greater extent than than 130 years ago, these deposits convey long been recognized every bit strange, says Christine Siddoway, a geologist at Colorado College, Colorado Springs. Many sandstone formations demonstrate layers of about type, signs they were position downward over fourth dimension inward distinct episodes yesteryear air current or flowing water. But the private grains inward the Tava sandstone, which typically are bits of quartz criterion from 125 to 250 micrometers across, are good mixed, together with they’re peppered amongst larger bits of quartz upward to three millimeters inward diameter. Once free-flowing only forthwith firmly cemented together amongst an iron-bearing mineral called hematite, the sand grains were apparently injected into cracks inward ancient granite—some of them every bit much every bit 6 meters wide—under high pressure. The now-solid Tava deposits apparently flowed from vast reservoirs of once-waterlogged sand, about of them containing to a greater extent than than 1 1000000 cubic meters of material.
“This is a real unusual [sandstone],” says Arlo Weil, a structural geologist at Bryn Mawr College inward Pennsylvania, who wasn’t involved inward the novel study. “It must convey been formed yesteryear a real rapid, chaotic process.”
The Tava sandstone is unusual for about other reason: It may endure the entirely large-scale deposit inward the public where sedimentary rocks such every bit sandstone convey been injected into crystalline rocks such every bit granite, Siddoway says. Normally, molten cloth flows into cracks inward sedimentary rocks together with and then solidifies, she explains.
For good over a century, geologists convey debated the historic stream of the Tava sandstone, Siddoway notes. Although the deposit patently must endure younger than the surrounding granite, which has an estimated historic stream betwixt 1.03 billion together with 1.09 billion years, about teams convey suggested that the Tava sandstone mightiness convey formed every bit late every bit 280 1000000 years ago. Now, analyses yesteryear Siddoway together with George Gehrels, a geologist at the University of Arizona (UA) inward Tucson, shed novel low-cal on when the deposits may convey formed.
For their study, the researchers analyzed samples of Tava sandstone collected at 6 sites nigh Colorado Springs. First, they extracted betwixt 100 together with 125 tiny zircons—tiny bits of erosion- together with chemical-resistant mineral—from each sample. Then they used uranium/lead dating to decide the historic stream of each zircon (the fourth dimension when its nurture stone crystallized). Most of the zircons were betwixt 1.33 billion together with 970 1000000 years old, together with none were younger than 850 1000000 years old, Siddoway says. Sometime after the zircons crystallized, perhaps millions of years later, these bits of mineral eroded out of their nurture stone together with ultimately ended upward beingness washed or blown into what is forthwith cardinal Colorado. So although the zircon ages render clues to the historic stream of the Tava sandstone, they aren’t definitive.
To assist narrow the attain of possible ages for the sandstone, Siddoway together with Gehrels compared the historic stream distributions of the Tava zircons amongst the historic stream distributions of zircons constitute inward other sandstone formations inward Colorado, Utah, northern Arizona, together with southern California. Statistically, the Tava distribution most closely matched the patterns inward sandstones that had been deposited betwixt 680 1000000 together with 800 1000000 years ago, the researchers volition written report inward an upcoming number of Lithosphere.
The paper’s results are “strong, compelling show that this historic stream attain [for the sandstone’s deposition] is correct,” says Peter Reiners, a geophysicist at UA who was non involved inward the novel study.
That was an interesting era inward Earth’s history, Weil says. An ancient supercontinent called Rodinia was breaking up, he notes, together with what is forthwith western North America was beingness stretched apart—a procedure that probable cracked the Colorado granites apart, creating voids that were all of a abrupt filled amongst immense amounts of waterlogged sand that had accumulated atop the granites or nearby. The novel findings “will alter [geologists’] perspective on the Rodinia breakup,” particularly regarding when the lawsuit occurred together with whether it happened inward several phases, he notes. They likewise propose that the Ute Pass mistake formed during that era, hundreds of millions of years earlier the Rockies were fifty-fifty born, making it much older than researchers convey previously suspected, he adds.
If the fractures hosting the Tava sandstone were indeed formed during the breakup of Rodinia, the stretching together with rifting of that supercontinent extended further eastward than previously suggested, Reiners notes.
It’s non even thence clear where the reservoirs of sand that flowed into the granite fractures millions of years agone were situated, Siddoway says. She together with her colleagues are forthwith trying to figure that out. But the sands “almost sure percolated downward from the surface into the older, underlying bedrock,” Reiners says. Scientists convey suggested that similar formations inward Sweden formed when the immense weight of glacial H2O ice forced sand together with other loose cloth into fissures inward underlying rocks. “These rocks are unusual together with non real common, only they’re non unheard of,” he says.