Metamorphic Evolution of a Tremolite Marble from the Dabie UHP Terrane, China: A Focus on Zircon
Penglei Liu , Zhenmin Jin
Journal of Earth Science ›› 2022, Vol. 33 ›› Issue (2) : 493 -506.
In this study, a tremolite marble from the Dabie ultrahigh-pressure (UHP) terrane, east-central China was investigated for its metamorphic evolution by focusing on zircon. The marble contains an amphibolite-facies assemblage of dolomite, Mg-calcite, tremolite, biotite, and plagioclase, while zircon in the marble witnesses a complex recrystallization and growth history under both amphibolite-and eclogite-facies conditions. Cathodoluminescence reveals eight characteristic zones for zircon. As indicated by mineral inclusions in zircon, two zones formed no earlier than amphibolite-facies retrogression and are too thin to date. The other six zones contain inclusions of dolomite, aragonite, diopside (X Na=Na/(Na+Ca)=0.11–0.14), garnet (X Ca=0.51–0.62, X Mg=0.21–0.23, X Fe=0.17–0.26, X Mn=0.01), phengite and rutile, and formed under eclogite-facies conditions. Phase equilibria calculations illustrat that the Na-richest diopside formed under UHP conditions. Being an accessory eclogite-facies mineral in the marble, the analyzed chemistry of garnet inclusions cannot be reproduced by phase equilibria calculations because solid-solution models for many other minerals don’t incorporate Mn-endmembers. The eclogite-facies zircon zones show low HREE contents and flat MREE-HREE distribution patterns, which are interpreted to have been determined by the low bulk-rock HREE content instead of the presence of accessary garnet in the marble. U-Pb dating yielded a large age dataset ranging from about 250 to 210 Ma for the eclogite-facies zircon zones. Statistically, the eclogite-facies ages are characterized by a Gaussian distribution with a median peak at 232 Ma. We propose that zircon experienced a “protracted” recrystallization and/or growth history in the tremolite marble during the Triassic subduction and exhumation.
Dabie / UHP / marble / mineral inclusion / recrystallization / zoned zircon / tectonics
| [1] |
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| [2] |
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| [3] |
|
| [4] |
|
| [5] |
|
| [6] |
|
| [7] |
|
| [8] |
|
| [9] |
|
| [10] |
|
| [11] |
|
| [12] |
|
| [13] |
|
| [14] |
|
| [15] |
|
| [16] |
|
| [17] |
|
| [18] |
|
| [19] |
|
| [20] |
|
| [21] |
|
| [22] |
|
| [23] |
|
| [24] |
|
| [25] |
|
| [26] |
|
| [27] |
|
| [28] |
|
| [29] |
|
| [30] |
|
| [31] |
|
| [32] |
|
| [33] |
|
| [34] |
|
| [35] |
|
| [36] |
|
| [37] |
|
| [38] |
|
| [39] |
|
| [40] |
|
| [41] |
|
| [42] |
|
| [43] |
|
| [44] |
|
| [45] |
|
| [46] |
|
| [47] |
|
| [48] |
|
| [49] |
|
| [50] |
|
| [51] |
|
| [52] |
|
| [53] |
|
| [54] |
|
| [55] |
|
| [56] |
|
| [57] |
|
| [58] |
|
| [59] |
|
| [60] |
|
| [61] |
|
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