豫西东秦岭造山带核部杂岩中钙质变质岩的变质作用演化

METAMORPHIC EVOLUTION IN CALCAREOUS ROCKS IN THE CORE COMPLEX OF EASTERN QINLING OROGENIC BELT, WESTERN HENAN

秦岭杂岩中的钙质变质岩经历了晋宁和加里东-海西两个巨构造-热旋回的强烈影响和改造。在加里东的深位(≥15km)接触热变晕的钙质变质岩中,保存了若干精美的非平衡结构。凭借非平衡结构的研究分析,重塑了接触热变质的递进变质和退变质阶段的反应形式以及冷却过程的P-T-X_(co_2)路径。

The polymetamorphic calcareous rocks of Qinling Complex in western Henan were intensively affected by both Jinninian Tectonothermal Cycle and Caledonian-Hercynian Tectonothermal Cycle. In the Jinning Cycle, the regional amphibolite-upper amphibolite facies metamorphism gave rise to three progressive metamorphic zones. The foresterite zone is distributed in the core, with the diopside zone and tremolite zone bordering on its south and north, respectively. The subsequent Caledonian-Hercynian Tectonothermal Cycle did not cause further growth of minerals throughout the region except for those rocks within the thermal aureole of some synchronous intrusive granites. In such an aureole in Shewei area, some nonequilibrium textures including corona,symplectite and exsolution lameller are well preserved in the calcareous rocks, which permits us to reconstruct the metamorphic reaction sequence of both prograde and retrograde processes and the P-T-X_(CO_2) trajectories during the cooling process. The prograde P-T path of the contact metamorphism is near isobaric heating; the metamorphic peak conditions are T≥750℃ and P=500～700MPa. The retrograde P-T path is near isobaric. In terms of the phase relationships from the thermodynamic calculated isobaric T-X_(CO_2) diagram, the X_(CO_2) for both carbonate rocks and meta-calcsilicate rocks decreased gradually with decrease of the metamorphic temperature.