Boron release and transfer induced by phengite breakdown in subducted impure metacarbonates
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The subchondritic Nb/Ta in both the continental crust and the depleted mantle remains enigmatic and is called the missing Nb paradox. We present partitioning data between biotite and granitic melt for experimental and natural samples that provide evidence that Nb is compatible in biotite and phengite. Nb can thus be enriched in the residue during partial melting of crustal rocks. Additionally, biotite and phengite in equilibrium with granitic melts preferentially incorporate Nb over Ta. Therefore incipient partial melting of biotite-rich crustal rocks produces restites with high Nb/Ta. Progressive melting of such rocks leads to the consumption of biotite and the formation of peritectic rutile or ilmenite, which retain the high-Nb/Ta signature. We suggest that such mid to lower crustal granulites could represent an important Nb-rich reservoir with high Nb/Ta. Similarly, high-Ti phengite that is present in deeply subducted sediments preferentially incorporates Nb over Ta. High-pressure incipient partial melting in the presence of residual phengite thus also produces restites with high Nb/Ta that could be subducted to the deeper mantle.
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Abstract: Energy‐dispersive X‐ray spectroscopy (EDS) is performed on different samples of external or fracture surfaces belonging to specimens used in piezonuclear tests [ Strain 45, 2009, 332; Strain (in press); Phys. Lett. A. 373, 2009, 4158]. For each sample, different measurements of the same crystalline phases (phengite or biotite) are performed to obtain averaged information of the chemical composition and to detect possible piezonuclear transmutations from iron to lighter elements. The samples were carefully chosen to investigate and compare the same minerals both before and after the crushing failure. Phengite and biotite, which are quite common in the Luserna stone (20 and 2%, respectively), are considered owing to the high iron concentration in their chemical compositions. The results of EDS analyses show that, on the fracture surface samples, a considerable reduction in the iron content (∼25%) is counterbalanced by an increase in Al, Si, and Mg concentrations.
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Combined with the microscope characteristic of thin section,This paper discussed the variety of ΔrG and its interrelation with temperatures and burried depth for the feldsparzation of plagioclase,chloritization of biotite and reduction of [UO2(CO3)3]4-.The result indicates that the feldsparzation of plagioclase can not be proceed without the presence of deep hydrothermal fluid.The reaction of chloritization of biotite owns the least ΔrG value,it falls at the firstly and then increases subsequently to positive value which suggest that the reaction can proceed easily under lower temperature.The ΔrG value for the reduction of [UO2(CO3)3]4-is negative in condition with alkaline and magnetite which shows that the reaction can proceed with any temperatures and pressures.The chloritization of biotite can provide potassium steadily in case of no external potassium source.The wider the intersectional temperature area of two reacitonis,the easier for feldsparzation of plagioclase in that deepness.And the feldsparzation of plagioclase takes place mostly beneth 2500 m depth.The appearance of typical mineral for acid fluid will indicate the rich uraninite in the area of potash metasomatism.
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Research Article| June 01, 1974 Orbicular Rocks of the Sandia Mountains, New Mexico TOMMY B. THOMPSON; TOMMY B. THOMPSON 1Department of Earth Resources, Colorado State University, Fort Collins, Colorado 80521 Search for other works by this author on: GSW Google Scholar DAVID L. GILES DAVID L. GILES 2Nord Resources, Inc., 2300 Candelaria, N. E., Albuquerque, New Mexico 87107 Search for other works by this author on: GSW Google Scholar Author and Article Information TOMMY B. THOMPSON 1Department of Earth Resources, Colorado State University, Fort Collins, Colorado 80521 DAVID L. GILES 2Nord Resources, Inc., 2300 Candelaria, N. E., Albuquerque, New Mexico 87107 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (6): 911–916. https://doi.org/10.1130/0016-7606(1974)85<911:OROTSM>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation TOMMY B. THOMPSON, DAVID L. GILES; Orbicular Rocks of the Sandia Mountains, New Mexico. GSA Bulletin 1974;; 85 (6): 911–916. doi: https://doi.org/10.1130/0016-7606(1974)85<911:OROTSM>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Orbicular rocks that occur within biotite-rich Precambrian granite of the Sandia Mountains in central New Mexico are of three types: (1) multishelled orbicules with alternating biotite- and plagioclase-rich shells, (2) plagioclase orbicules with or without a discontinuous biotite shell near the orbicule margin, and (3) orbicules with plagioclase cores surrounded by thin concentric bands of finely crystalline biotite alternating with plagioclase. Cores of the orbicules consist of fragments of biotite monzonite, plagioclase, or hornfels.Petrographic data on fragment reactions during orbicule formation, an aplite dikelet that cuts the orbicule zone, spacing of orbicule shells, and chemical analyses suggest that these orbicular rocks formed by reactions between xenoliths and magmatic fluids during crystallization of the granite. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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