Metamorphic Evolution of a Tremolite Marble from the Dabie UHP Terrane, China:A Focus on Zircon

• 作者: Penglei Liu Zhenmin Jin
• 来源期刊: 地球科学学刊（英文版）
• 年，卷（期）: 2022,（2）
• 页码范围: 493-506
• 页数: 14页
• 语种: 英文

摘要

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 con-tains 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 in-dicated by mineral inclusions in zircon, two zones formed no earlier than amphibolite-facies retrogres-sion and are too thin to date. The other six zones contain inclusions of dolomite, aragonite, diopside (XNa=Na/(Na+Ca)=0.11-0.14), garnet (XCa=0.51-0.62, XMg=0.21-0.23, XFe=0.17-0.26, XMn=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 calcula-tions 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 pres-ence 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"pro-tracted"recrystallization and/or growth history in the tremolite marble during the Triassic subduction and exhumation.