{"id":29468,"date":"2021-11-04T17:43:29","date_gmt":"2021-11-04T16:43:29","guid":{"rendered":"https:\/\/karmaka.de\/?p=29468"},"modified":"2021-11-04T17:47:34","modified_gmt":"2021-11-04T16:47:34","slug":"infiltration-metasomatism-of-the-allende-coarse-grained-calcium-aluminum-rich-inclusions","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=29468","title":{"rendered":"Infiltration metasomatism of the Allende coarse-grained calcium-aluminum-rich inclusionsOPEN ACCESS<\/span> "},"content":{"rendered":"\n

Alexander N. Krot, Michail I. Petaev & Kazuhide Nagashima<\/p>\n\n\n\n

Progress in Earth and Planetary Science, Volume 8, Article number: 61 (2021)
Published: 4 November 2021<\/p>\n\n\n\n

LINK (OPEN ACCESS)<\/strong><\/a>
PDF (OPEN ACCESS)<\/strong><\/a><\/p>\n\n\n\n

“We report on the mineralogy, petrography, and O and Al-Mg isotopic systematics of secondary mineralization in the metasomatically altered igneous Ca,Al-rich inclusions (CAIs) [compact type A (CTA), B1, B2, forsterite-bearing B (FoB), and C] from the CV3 carbonaceous chondrite Allende. This alteration affected mainly melilite, and to a lesser degree anorthite, and resulted in the formation of a variety of secondary minerals, including adrianite, Al-diopside, andradite, anorthite, calcite, celsian, clintonite, corundum, dmisteinbergite, ferroan olivine, ferroan monticellite, ferroan Al-diopside, forsterite, grossular, heazlewoodite, hedenbergite, hutcheonite, kushiroite, margarite, monticellite, Na-melilite, nepheline, pentlandite, pyrrhotite, sodalite, spinel, tilleyite, wadalite, and wollastonite. The secondary mineral assemblages are mainly defined by chemical compositions of the primary melilite replaced and elements introduced by an aqueous fluid. Gehlenitic melilite (\u00c5k<35) in CTAs and mantles of B1s is mainly replaced by anorthite + grossular; clintonite, corundum, spinel, and Al-diopside are minor. \u00c5kermanitic melilite (\u00c5k35-90) in type B2s, FoBs, and cores of B1s is replaced by the grossular + monticellite + wollastonite, grossular + monticellite, and grossular + Al-diopside assemblages; forsterite, spinel, clintonite, and Na-melilite are minor. In type Cs, lacy melilite (\u00e5kermanitic melilite with rounded inclusions of anorthite) is pseudomorphically replaced by the grossular + forsterite + monticellite and grossular + Al-diopside assemblages; Na-melilite is minor. Primary and secondary anorthites in the peripheral portions of CAIs are replaced by nepheline, sodalite, and ferromagnesian olivine. Some CAIs contain voids and cracks filled by andradite, hedenbergite, wollastonite, \u00b1sodalite, \u00b1grossular, \u00b1monticellite, \u00b1tilleyite, and \u00b1calcite. All CAIs studied are surrounded by Wark-Lovering rims, fine-grained matrix-like rims composed of lath-shaped ferroan olivine and abundant nepheline grains, and a layer of salite-hedenbergite pyroxenes + andradite + wollastonite. Grossular associating with monticellite, Al-diopside, and forsterite and replacing \u00e5kermanitic melilite (27Al\/24Mg ~ 2) has high 27Al\/24Mg ratios (30\u2212100) and shows no resolvable excess of radiogenic 26Mg (26Mg). The 27Al\/24Mg ratios (7\u221210) and 26Mg<\/em> (2\u22123\u2030) in the nearly monomineralic grossular veins crosscutting gehlenitic melilite are similar to those of the host melilite and plot along a regression line with 26Al\/27Al ratio of ~5\u00d710\u22125. Oxygen isotopic compositions of secondary minerals in the most Type Bs measured in situ with the UH Cameca ims-1280 and matrix-matched standards plot along mass-dependent fractionation line with \u220617O of ~ \u22123\u00b12\u2030 with \u03b418O ranging from ~0 to ~10\u2030. Primary melilite and anorthite in the host CAIs are similarly 16O-depleted, whereas spinel, forsterite, and most Al,Ti-diopside grains have 16O-rich compositions (\u220617O ~ \u221225\u00b12\u2030). Secondary grossular and forsterite in type Cs and type B1 CAI TS-34 show a range of \u220617O, from ~ \u221215 to ~ \u22121\u2030; the 16O-enriched compositions of grossular and forsterite plot along the carbonaceous chondrite anhydrous mineral line. The similar ranges of \u220617O and positions on the three-isotope oxygen diagram are observed for primary anorthite; melilite is generally 16O-depleted compared to anorthite (\u220617O ~ \u22125 to \u22121\u00b12\u2030); spinel and fassaite are 16O-rich (except very Ti-rich fassaite in TS-34 and CTA CAIs). We conclude that Allende CAIs experienced an open-system in situ metasomatic alteration at relatively high temperatures (200-250 \u00b0C) in the presence of CO2- and H2O-bearing fluid with \u220617O of ~ \u22123\u00b12\u2030 followed by thermal metamorphism at ~ 500 \u00b0C on the CV chondrite parent asteroid. During the alteration, most elements were mobile: Si, Na, Cl, K, Fe, S, and Ni were introduced; Al, Ti, Mg, and Ba were locally mobilized; Ca and some Mg and Al were lost from the host inclusions. The alteration occurred after nearly complete decay of 26Al, >3 Ma after crystallization of CAIs with the canonical (26Al\/27Al)0 of (5.25\u00b10.02)\u00d710-5; 26Mg* in grossular was inherited from the primary melilite and provide no chronological significance. Oxygen isotopic heterogeneity of primary minerals in the Allende CAIs at least partly is due to isotopic exchange with an aqueous fluid that largely affected melilite, anorthite, perovskite, Zr- and Sc-rich oxides and silicates, and possibly very Ti-rich fassaite.”<\/p>\n","protected":false},"excerpt":{"rendered":"

Alexander N. Krot, Michail I. Petaev & Kazuhide Nagashima Progress in Earth and Planetary Science, Volume 8, Article number: 61 (2021)Published: 4 November 2021 LINK (OPEN ACCESS)PDF (OPEN ACCESS) “We report on the mineralogy, petrography,…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[66,9,585,14,2531,2532,2533],"tags":[108,1846,3273,4890,1812,5181,5479,675,727,725],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/29468"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=29468"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/29468\/revisions"}],"predecessor-version":[{"id":29469,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/29468\/revisions\/29469"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=29468"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=29468"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=29468"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}