科研之友
微信
新浪微博
Facebook
分享链接
摘要
Epidote-group minerals (EGM), including some of unusual chemical compositions, occur with pyrite and pyrrhotite in the Lower Paleozoic carbonaceous amphibole schist of the meta-ophiolitic Pernek Group at Rybnfcek, near Pezinok, southwestern Slovakia. Euhedral to anhedral dissakisite-(La), mukhinite, and clinozoisite are associated with V-and Cr-rich garnet (goldmanite - grossular - uvarovite solid-solution), V-and Cr-rich muscovite, amphibole-group minerals (magnesiohornblende, tremolite, actinolite, and edenite), diopside, titanite, albite, quartz, siderite and sulfide minerals (pyrite, pyrrhotite, rarely chalcopyrite and sphalerite). Strong compositional zoning and three stages of EGM formation were found. The core of EGM grains consists of V- and Cr-rich dissakissite-(La) (V <= 0.33 apfu, Cr <= 0.44 apfu); it grades into REE-rich mukhinite of varying Cr contents (REE <= 0.46 apfu, 0.13 to 0.43 apfu Cr). Clinozoisite I, which is V- and Cr-rich (V <= 0.40 apfu, Cr <= 0.42 apfu), occurs as an overgrowth upon the dissakisite-mukhinite cores. A second generation of V-, Cr- and REE-poor clinozoisite (clinozoisite II) has replaced mukhinite and clinozoisite I at the grain rim, and it is also found in veins that cut the grains. Many substitutions can change the compositions of the EGM: V(3+) and Al(3+) cause the VAl(-1) substitution; CrAl(-1) and CrV(-1) substitutions may be extensive, but both are of limited extent, and Cr(3+) is partly independent of the contents of substituents; Mg(2+) substitution reflects the REEMgCa(-1)Al(-1), REEMgCa(-1)V(-1), and REEMgCa(-1)Cr(-1) exchange-vectors. Most REE patterns show enrichment in the light REE. Chondrite-normalized REE patterns show a negative Ce anomaly and a slightly positive Eu anomaly in clinozoisite I and dissakisite-(La), but mukhinite lacks this Eu anomaly. Dissakisite-(La) most likely originated at or near the peak conditions of contact thermal metamorphism induced by the Hercynian-age intrusion of the Modra granitic massif, whereas mukhinite and clinozoisite I formed during retrogression. Clinozoisite II may reflect the younger (Alpine?) low-grade metamorphic overprint.
- 出版日期2010-6
