Eclogite

Classification：Metamorphic Rock

Eclogites are mainly composed of garnet and omalite. They are a very beautiful rock, which is a metamorphic rock formed under high-pressure environment, and the original rock is basalt.

One of the regional metamorphic rocks. It is the largest rock in the metamorphic rock. It is generally believed that it is formed by the metamorphism of basic and ultrabasic magmatic rocks under great pressure conditions, and the temperature conditions are not limited, which can be formed within the range of low temperature to high temperature. The main mineral components are light red garnet and green omen. They are mostly medium coarse grain, granular texture and massive structure, with deep color. Lenslike or small rock masses are often found in gneiss.

Eclogite introduction:
Eclogiteeclogite is a metamorphic rock. It is formed by regional metamorphism. It is mainly composed of high-pressure metamorphic rocks composed of ommite and magnesium rich garnet. The omphacite containing diopside, jadeite, clinopyroxene, garnet pyrope for calcium iron. It contains quartz, kyanite, spinel, naughty pyroxene, olivine, Jin Hongshi, stonalite, and some other minerals such as blue amphibole, common hornblende, xanite, sphore, but not plagioclase.
The Eclogite is mainly composed of garnet and omyroxene, the two is more than 80%, the garnet is a ferro - Al - Garnet - a series of calcite - alalite, and the diopyroxene, calcite, jadeite, and conical pyroxene. The mineral assemblages include a small number of secondary minerals, coriite, corundum, diamond, trapezite, polysilicon muscovite, kyanite, epidote, antra, blue amphibole, hornblende, Jin Hongshi and so on.
Eclogite is a low and medium low temperature metamorphic rock in petrological classification. The surface outcrop is very rare and its occurrence is very complex. It is usually in the nuclear part of the orogenic belt and often represents the boundary of the paleo plate. It can be a inclusion in the Kimberley rock, and can also be produced in the pomegranate peridotite. Eclogite can be associated with some granulite facies rocks and can also be associated with the blue amphibole schist in the high pressure metamorphic belt.

Characteristics and causes:
Generally speaking, Eclogite is dark, coarse-grained, and granular. Often with the characteristics of secondary minerals such as kyanite named Eclogite. The chemical composition of Eclogite is similar to that of basalt, but its occurrence and origin are rather complicated.

Eclogite geological sites:
The typical Eclogite should be rocks of magnesium aluminum garnet and omiroxene, Eclogite microstructural map, granular crystal structure, 160 times magnification, green pyroxene and red magnesium aluminum garnet. The color of minerals omphacite is green, dark green, light green, light red, red, magnesium aluminum garnet is dark red. It is a massive structure with unequal grain structure. A small amount of Eclogite has undergone strong plastic deformation and the crystallization of minerals under stress.
Eclogite can be produced as a inclusion in the Kimberley rock; it can also occur in the pomegranate peridotite intrusive body; it can be associated with the granulite and amphibolite facies, and can also occur in the blue schist of the high pressure metamorphic belt. The difference of occurrence reflects the complexity of the origin of Eclogite. The main points of origin of Eclogite are as follows: Eclogite is formed in the mantle, is the crystalline product of the mantle material at a certain depth, or the remnant of the partial melting of the mantle rocks; Eclogite is the product of the basalt in the deep crust of the continental crust; Eclogite is formed by the crystallization of basaltic magma under the high rock pressure. Eclogite is the product of deep crust metamorphism. The pressure is very high, 1.1 ~ 1.5Gpa, up to 3Gpa. The temperature range is wide: 450~750 degrees centigrade.
There are 3 kinds of production states: (1) inclusions occur in Kimberley rock and stratified ultrabasic rocks. The clip was layered, lens produced in the amphibolite and granulite facies rocks. In a sandwich or lens produced in hornblende facies rocks in hard stone column. It is generally believed that it is formed under extremely high pressure, but the temperature varies widely. Kimberley rock Eclogite package that is a product of mantle both body waves.
According to petrography, mineral composition, chemistry and thermodynamics analysis, it shows that the Eclogite has recorded 6 stages of metamorphism and has "clockwise" PT evolution trajectory. From stage I, stage II to stage III, the characteristics of the progressive metamorphism are shown near the isothermal supercharging, and the maximum pressure in stage III reaches P=2.53 GPa, and the IV and V stages show a process of increasing temperature and depressurization, and the temperature is up to T=627 C at the fifth stage, while the phase VI is the process of reducing temperature and depressurization. The process implies that the high-pressure plate may be in a non uniform state during the process of subduction and reentry. It is presumed that the process of increasing temperature and degeneration in the later period of Zhujiachong Eclogite may be caused by the recovery of the disturbed geothermal line, the "heat dissipation" of the process of ultra high pressure Eclogite degeneration, and the sensitivity of this kind of Eclogite to the temperature change.

Structural analysis:
Geochemical and structural analyses of Eclogite and amphibolite indicate that the retrograde metamorphism of Eclogite is strongly localized, which is consistent with the localization of deformation. Non conservative elements (K, Rb, Cs and Ba) have similar characteristics in these two kinds of Eclogite. The retrograde metamorphism of ultra high pressure Eclogite phase, Eclogite phase to amphibolite or even lower metamorphic facies has little effect on non conservative elements (K, Rb, Cs, Ba, etc.). In the retrograde metamorphism of Eclogite, omenite or garnet decomposes into mineral assemblages of plagioclase + amphibole, which requires considerable amount of water.

Eclogite structural analysis:
Since the above elements are soluble and easy to migrate in aqueous solutions, the degenerative Eclogite should show considerable changes in these non conservative elements if the degenerative process is accompanied by a large number of dispersed fluids. Therefore, the above characteristics indicate that in the process of retrograde metamorphism, there is basically no foreign liquid, and the source of the fluid is formed in dehydration or decomposition of the anhydrous mineral in the reputation; these fluids are only limited in migration, and the conservative elements dissolved in these fluids are redistributed near the place.
The results are consistent with the observations based on isotopic, fluid inclusions, petrography and Eclogite's deformation structures. The finite and internal buffer fluid derived from the dehydration and dehydration of anhydrous minerals in the reputation can explain (1) why the retrogression and Eclogite ductile shear bands are highly localized in Su Lu's strongly retrograde metamorphic Eclogite; (2) there is a large amount of apatite even in the strong degeneration domain.
The form and scale of the above inference fluid is helpful to understand the deformation characteristics of Sulu ultra-high pressure Eclogite. In the CCSD main hole and the surface Eclogite, ductile deformation is usually highly regionalized, often coincided with highly degenerated mass domains. This relationship also shows the high localization of the fluid and the appearance of the pipe flow, which not only promotes shear deformation, but also is the main factor to promote the partial retrogression of Eclogite.

The process of degeneration:
The main hole of the Chinese Continental Scientific Drilling is located on the typical ultrahigh pressure metamorphic belt of Dabie Su Lu. In the core of 0-2000m, Eclogite accounts for more than 50%. Most of the Eclogite experienced different degrees of retrogression. According to the degenerative quality of OMP and garnet, the main minerals in Eclogite.

Eclogite evolution process:
The retrogression process of 0-2000mEclogite can be divided into 2 major stages, 4 sub stages: the first major stage (also divided into slight retrogression, partial retrogression) and second major stages (also divided into retrogression and retrograde metamorphism). The general trend of retrogression is that the garnet is gradually replaced by the chive amphibole or the black mica + epidote, and the diopenite is gradually replaced by the hornblende + albite, and the Jd content decreases gradually and is partially converted to the neon pyroxene. The temperature and pressure conditions of Eclogite in the process of retrograde metamorphism are: peak metamorphism temperature is 697-831 C, pressure is about 3.0Gpa, the temperature of partial retrogression stage is 629-776 C and pressure 1.2-1.6Gpa; the temperature of retrograde metamorphism stage is 550-650 C and pressure 0.5-0.7Gpa; the temperature of the stage of strong retrograde metamorphism is 300~400, and the pressure 0.30-0.35Gpa. According to the characteristics of rock, mineral and temperature and pressure conditions, it is inferred that the process of Eclogite's reentry has experienced two major stages: the first major stage is the rapid return of the near isothermal depressurization (Eclogite has experienced the first stage of retrogression during this period), and the second stage is the slow rise of temperature lowering and lowering (Eclogite then went through the first step. " Two stages of retrogression). The retrograde metamorphism of omomite is not only a symbol of the two stage of Eclogite retrograde metamorphism, but also a sign to distinguish the two exhumation stages.