摘要
荣城大疃地区的榴辉岩及有关的超基性岩出露在胶南-苏北构造混杂岩带的东北部。榴辉岩在超基性岩和片麻岩中呈构造块体产出。前者的原岩为玄武岩或玄武质岩浆早期分离结晶的堆晶岩在660～790℃和13～18(×10~5kPa)条件下变质形成,后者为辉长质堆晶岩在660～790℃和15～19(×10~5kPa)条件下变质形成。石榴二辉橄榄岩本身也呈构造块体产于片麻岩中,经历了739±80℃～1033±95℃和45～52.7(×10~5kPa)的低温高压变质。这些岩石的形成与海西—印支期华北板块与扬子板块之间的消减碰撞造山作用有关。
The petrogenesis of the eclogites and related peridotitic rocks in Datuan area of Rongcheng County, a part of the northeastern section of the tectonic melange zone in Southern Shandong-Northern Jiangsu region has been studied in this paper by means of petrological, mineralogical, petrochemical and geochemical methods. According to their occurrence,the eclogites can be divided into type P, occurring in peridotitic body as tectonic fragments, and type G, occurring in gneisses as tectonic blocks. The former can be divided into two subtypes in protolith,namely, subtype P_1 derived from basaltic melt, and subtype P_2 derived from cumulate formed by early fractional crystallization of basalitic magma. The protolith of type G eclogites has been considered to be gabbroic cumulate.
These types of eclogites are different from each other in petrochemistry and REE geochemistry. The subtype P_1 eclogite has a wide range of chemical composition following the evolution trend of basaltic magma. They are of oceanic affinity in bulk rock composition, and show REE pattern similar to that of OIB or E-type MORB. The type P_2 eclogites have a rather constant chemical composition characterized by high content of MgO and CaO and low content of TiO_2 and FeO in comparison with other types of eclogites.Their REE patterns are of an inverted 'V' shape,indicating that they are of cumulate origin. The type G eclogites have a considerable range of chemical composition. As a whole, however, they are characterized by high content of Al_2O_3 ,and low content of MgO and Na_2O. Among them, some show the LREE-and MREE-rich distribution patterns, and some an obviously positive Eu anomaly typical of gabbroic cumulate.
By use of geobarometers and geothermometers, the P-T conditions for ecrystallization of various types of eclogites have been estimated as follows:1300～1800 MPa and 660～790℃ for type P and 1500～1900 MPa and 660～790℃ for type G. However, the P-T conditions for crystallization of garnet lherzolites are 4500～5270 MPa and 739±80～1033±95℃. It may be inferred from the data in this paper that the formation of the eelogites was related to the late Hercynian-Indosinian subduction-collision orogene between the North China and Yangtze Paleocontinents.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
1992年第1期27-39,T001,共14页
Acta Petrologica Sinica
基金
国家自然科学基金
关键词
榴辉岩
成因
岩石学
山东
Petrogenesis
Eclogite
Peridotitic rock
Rongcheng
Shangdong
