Hexbyte Glen Cove Mineral dating reveals new clues about important tectonic process

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Minerals are visible in rock samples from the coast of Oman. Scientists said these rocks may reveal new information about subduction, an important tectonic process on Earth. Credit: Joshua Garber / Penn State, Creative Commons

Ancient rocks on the coast of Oman that were once driven deep down toward Earth’s mantle may reveal new insights into subduction, an important tectonic process that fuels volcanoes and creates continents, according to an international team of scientists.

“In a broad sense this work gives us a better understanding of why some fail while others set up as long-term, steady-state systems,” said Joshua Garber, assistant research professor of geosciences at Penn State.

Subduction occurs when two collide, and one is forced under the other. Where oceanic and meet, the denser oceanic plates normally subduct and descend into the mantle, the scientists said.

Occasionally, oceanic plates move on top, or obduct, forcing continental plates down toward the mantle instead. But the buoyancy of the continental crust can cause the to fail, carrying the material back toward the surface along with slabs of oceanic crust and upper mantle called ophiolites, the scientists said.

“The Samail Ophiolite on the Arabian Peninsula is one of the largest and best exposed examples on the surface of the Earth,” Garber said. “It’s one of the best studied, but there have been disagreements about how and when the subduction occurred.”

The team, led by Penn State scientists, investigated the timing of the subduction using nearby rocks from the Saih Hatat formation in Oman, which was subducted under the Samail Ophiolite, according to the researchers.

Heat and pressure from the process created garnet, zircon and rutile crystals in a key suite of highly metamorphosed rocks that saw the most extreme conditions during subduction. Using state-of-the-art dating techniques, including measuring isotopic dates and trace elements, the scientists determined these minerals all formed at roughly the same time 81 to 77 million years ago.

“What’s interesting about this is that they were all dated by slightly different methods, but they all gave us essentially the same results,” Garber said. “This tells us that all the minerals in the rocks have a coherent story. They all record the same metamorphic episode at the same time.”

The findings, published in the Journal of Geophysical Research: Solid Earth, dispute previous results that estimated the event began 110 million years ago and happened in separate phases, the scientists said.

“What our findings suggest is that this continental material was not subducted deep into the mantle a long time before the ophiolite formed as previously thought,” Garber said. “Our data supports a nice sequence of events that happened in a tighter window and that makes more geological sense.”

The scientists said the subduction of the continental margin occurred after the obduction of the Samail Ophiolite. The most deeply subducted continental material was likely anchored to more dense rocks, and when this anchor broke, the buoyant continental rocks exhumed, first quickly, and then slowly during a lengthy residence in the lower to middle crust. It eventually become exposed in tectonic windows through the ophiolite.

“Subduction is a really big part of tectonics on Earth,” Garber said. “It’s the major recycling mechanism for surface material to the deeper , so understanding how they eventually evolve into stable subduction zones or how they end very quickly is of great interest. I think here we’ve nailed down why this subduction zone ended and the sequence of events that came with it.”

More information:
Joshua M. Garber et al, Dating Continental Subduction Beneath the Samail Ophiolite: Garnet, Zircon, and Rutile Petrochronology of the As Sifah Eclogites, NE Oman, Journal of Geophysical Research: Solid Earth (2021). DOI: 10.1029/2021JB022715

Mineral dating reveals new clues about important tectonic process (2022, February 12)
retrieved 13 February 2022
from https://phys.org/news/2022-02-mineral-dating-reveals-clues-important.html

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Hexbyte Glen Cove New data show a number of opportunities exist for states to lift working families out of poverty with the earned income thumbnail

Hexbyte Glen Cove New data show a number of opportunities exist for states to lift working families out of poverty with the earned income

Hexbyte Glen Cove

The Earned Income Tax Credit (EITC), in place in over half of all US states, are estimated to help lift 5.6 million out of poverty, yet gaps remain, according to new data published today to LawAtlas.org.

As of August 1, 2020, 29 and the District of Columbia have an EITC that supplements the federal EITC and provides tax relief on for working families and individuals. Across states, eligibility requirements, refundability, and notification of the policy vary:

  • Geographically, a majority of northeastern states have adopted a state EITC law. Fewer such state EITC policies exist among the southeast and states.
  • Of the 30 jurisdictions that offer a state EITC, nine adopt the federal EITC eligibility requirements. The remaining 21 have implemented state-specific eligibility requirements.
  • If the state EITC exceeds a taxpayer’s liability, only four states provide a full refund; 21 states provide a partial refund, and six states offer a non-refundable credit to eligible taxpayers.
  • The federal EITC benefit is currently available to eligible taxpayers ages 25 to 65 years. Only four jurisdictions (three states and DC) have extended the EITC benefit beyond the required age to include taxpayers under the age of 25.
  • Fifteen jurisdictions require notification of the state EITC to tax filers. Of those, only 10 require the state to notify benefit recipients of the state EITC.

“These data offer a look into how the state Earned Income Tax Credit laws vary across the United States. They identify opportunities to expand state EITC laws to assist more working people and include younger workers currently not eligible for the Federal EITC,” said Adam Lustig, the manager of the Promoting Health & Cost Control in States initiative at Trust for America’s Health, which is the umbrella project for these data.

These data contribute to a growing body of research that has shown state EITCs may improve , most significantly among and children.

“Although studies have highlighted the positive health effects of state EITC, especially among mothers and children, there is still much to learn,” said Lindsay Cloud, JD, director of the Center for Public Health law Research Policy Surveillance Program, which created the data. “This dataset is a foundational resource for anyone interested in understanding the extent of these income security benefits on health, well-being, and equity across the US.”

The Promoting Health and Cost Control in States initiative’s legal data resources are a collaboration of the Temple University Center for Public Health Law Research with Trust for America’s Health, and support from the Robert Wood Johnson Foundation. The Earned Income Tax Credit dataset is the fourth in a series of datasets on laws and policies that can support cost-savings for states and promote and well-being.

More information:
Center for Public Health Law Research Policy Surveillance Program. Earned Income Tax Credit Laws. October 28, 2020. lawatlas.org/datasets/earned-i … come-tax-credit-laws

New data show a number of opportunities exist for states to lift working families out of poverty with the earned income (2020, October 29)
retrieved 29 October 2020
from https://phys.org/news/2020-10-opportunities-states-families-poverty-income.html

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