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海南岛屯昌晨星地区变基性岩体原岩可能包括辉长岩(粗粒的斜长角闪岩)、辉长-辉绿岩(中细粒和中粗粒的斜长角闪岩)和枕状熔岩(细粒或块状斜长角闪岩)。由于受多期变质和蚀变作用的影响,组成这些岩石的多数矿物如角闪石、斜长石和绿泥石等常表现两个或两个以上的世代。角闪石环带矿物化学分析表明,从核到边,钛、铝、(钠+钾)含量增长,反映了压力和温度同时升高的进变质演化过程;相反,角闪石环带从核部到边部钛、铝和钾+钠含量降低,则暗示温度和压力同时降低而进入另一个退变质演化阶段。所获得的 Sm-Nd 全岩及角闪石的内部等时线年龄为128±12 Ma、Rb-Sr 全岩等时线年龄分别为131.8±6.2 Ma和344±11Ma。根据角闪石环带、矿物共生组合、微结构以及变质温压条件的半定量计算和同位素定年,屯昌晨星地区变基性岩体的变质作用可能经历了三个演化阶段。第一阶段(～527～450 Ma)可能记录了与洋底变质作用有关的(亚)绿片岩相至角闪岩相条件,早期的阳起石、钙质角闪石及镁铁质角闪石残余核为该阶段的产物;第二阶段(～330～240 Ma)进变质作用达到高峰的P=～0.9 GPa、T=～700℃,显示了过渡的高角闪石相-麻粒岩相变质条件。广泛的剪切变形及韭闪质普通角闪石-韭闪石边是该阶段的产物;第三阶段(～130 Ma～90 Ma)显示一个绿片岩相变质条件(P=～0.1～0.3 GPa、7=～300～400℃),可能与区域/热接触变质有关。因而屯昌晨星地区变基性岩体的变质作用演化显示了一个逆时针 P-T-t 轨迹,最可能与古太平洋板块俯冲导致的大陆边缘裂解及洋壳化和随后的年轻洋壳消亡、陆(华南大陆)-陆(印支板块)碰撞事件有关。
The original rocks of the metamorphic rocks in the Tunchang area of Tunchang, Hainan Island may include gabbro (coarse-grained amphibolite), gabbro-diabase (medium and coarse-grained amphibolite) And pillow lava (fine-grained or massive amphibolite). Due to the multistage metamorphism and alteration, most of the minerals that make up these rocks, such as amphibole, plagioclase and chlorite, often exhibit two or more generations. The chemical analysis of amphibole ring zone mineralization shows that the increase of (Na + K) content from core to edge reflects the progressive evolution of pressure and temperature at the same time. On the contrary, Decreasing the contents of titanium, aluminum, potassium and sodium from the edge to the edge implies that the temperature and pressure decrease at the same time and enter another stage of retrogressive metamorphism. The obtained Sm-Nd whole rock and amphibole have an internal isochron age of 128 ± 12 Ma and an isochron age of 131.8 ± 6.2 Ma and 344 ± 11 Ma for Rb-Sr. According to the semi-quantitative calculation of hornblende zone, mineral assemblage, microstructure, metamorphic thermo-compression conditions and isotopic dating, the metamorphism of the metamorphic rocks in Tunxing area may have experienced three stages of evolution. The first stage (~ 527 ~ 450 Ma) may record the (sub) greenschist facies to amphibolite facies related to the metamorphism of the ocean floor. The early stage actinolite, calcareous amphibole and mafic horn flash The residual core of the rock is the product of this stage. In the second stage (~ 330-240 Ma), the metamorphism peaked at P = ~ 0.9 GPa and T = ~ 700 ℃, indicating that the transitional hornblende-granulite facies Metamorphic conditions. Extensive shear deformation and allochryseriaceous amphibole-leechesite facies are the product of this stage; the third stage (~ 130 Ma ~ 90 Ma) shows a greensquam metamorphic condition (P = ~ 0.1 ~ 0.3 GPa , 7 = ~ 300 ~ 400 ℃), may be related to regional / thermal contact deterioration. Thus the metamorphic evolution of the metamorphic rocks in the Tunchang area shows a counterclockwise PTt path most likely to be caused by the continental margin cracking and oceanic crustal subduction and subsequent extinction of the young oceanic crust caused by the subduction of the Paleo-Pacific plateau ) - Lu (Indo-China Plate) collision event.