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The study focuses on the comparison of the chemical and mineral composition of Lunar regolith probes from Luna-16, -20, -24 stations and their the seacontinent environments. Using microprobe JXA-8200 and JSM-5610LV (400 analyses, 50 images, 9 fragments of layer-by-layer core samples) 18 mineral phases and their 12 varieties were diagnosed. The most common are ironmagnesium and calcium-bearing varieties of silicates – anortite, clinopyroxenes and olivine. The typomorphic features of rock-forming minerals in two types of the lunar surface are discussed. The composition of chromespinelids is demonstrated on a triangular prism diagram.

It is a general tendency that epidote, which is a typical greenschist facies mineral, is scarce in the lower oceanic crust, in spite of the widespread occurrence of the other minerals indicative of similar temperature conditions such as chlorite, actinolite, prehnite and serpentine. To find the cause of this, we carried out petrological analyses of lower crustal rocks of the Oman ophiolite sampled by the Oman Drilling Project of the International Continental Scientific Drilling Program (ICDP). Petrographic observations revealed the tendency, as expected, that the amount of epidote formed by static alteration of plagioclase decreases with depth. Because mineral assemblages indicative of a wide range of temperature conditions from amphibolite to subgreenschist facies occur throughout the cores without systematic variations of abundance, the decrease of epidote amount cannot be explained by the difference of temperature condition of alteration. Petrographic observations also revealed that epidote is absent or rare in rocks containing serpentinized olivine in contrast to prehnite showing a close association with serpentinization of olivine. In an exceptional sample containing both epidote and serpentinized olivine, epidote occurs with chlorite that cuts or replaces plagioclase, mantles adjacent olivine and is connected with chlorite + lizardite veins cutting mesh‐forming serpentine veins. The distribution and mode of occurrence of epidote suggest decoupling of its formation with the main stage of serpentinization. Serpentine veins cutting olivine to form mesh texture are typically lizardite with magnetite ribbons at vein centres and have compositions of lizardite–cronstedtite solid solution at vein margins or in magnetite‐free veins, suggesting a chemical condition with low silica and low oxygen potentials at an early stage of serpentinization. Thermodynamic modelling for olivine and plagioclase alteration at greenschist facies conditions indicates that silica potential for plagioclase alteration to form prehnite + chlorite and epidote + chlorite could be higher than for olivine serpentinization. On the other hand, oxygen potential for the prehnite + chlorite formation is lower than for the epidote + chlorite formation and is comparable with that for olivine serpentinization. From the observations and analyses, it is concluded that epidote formation is inhibited by olivine serpentinization, which maintains a reducing condition for alteration in the lower oceanic crust. [ABSTRACT FROM AUTHOR]

Loveringite, a rare member of the crichtonite group with nominal formula (Ca,Ce)(Ti,Fe,Cr,Mg)21O38, was found in the Khamal layered mafic intrusion, the first known locality for this mineral in the Arabian Shield. The Khamal intrusion, a large post-collisional mafic complex, is lithologically zoned, bottom to top, from olivine gabbro through gabbronorite, hornblende gabbro, anorthosite, and diorite to quartz diorite. Loveringite is found near the base of the complex, as an intercumulus phase in olivine gabbro. Most loveringite grains are homogeneous, although a few grains are zoned from cores rich in TiO2, Al2O3, Cr2O3, and CaO towards rims rich in FeO*, ZrO2, V2O3, Y2O3, and rare earth elements (REE). Petrographic relations indicate that loveringite formed after crystallization of cumulus olivine, pyroxenes, and plagioclase. Anhedral and corroded crystals of loveringite are surrounded by reaction rims of Mn-bearing ilmenite and baddeleyite, suggesting that the residual liquid evolved into and subsequently out of the stability field of loveringite. The budget of incompatible elements (Zr, Hf, REE, U, and Th) hosted in loveringite is anomalous for a primitive mafic liquid. Saturation in loveringite is likely the result of early contamination of the primary melt by anatexis of country rock, followed by isolation of evolving liquid in intercumulus space that restricted communication with the overlying magma chamber. The zoned crystals likely reflect diffusive equilibration between residual loveringite grains and their reaction rims of ilmenite. [ABSTRACT FROM AUTHOR]

To understand the similarity and diversity of serpentinization processes in different rock systems, gabbroic rocks recovered from IODP Site U1415 at the Hess Deep Rift were examined and compared with peridotites from the adjacent ODP Site 895. Textural observations, micro-Raman spectroscopic analyses and electron microprobe analyses indicated that most of the olivine-replacing serpentine in the gabbroic rocks lack the mixing with brucite, which is common in peridotites. At least three stages of serpentinization are observable in the gabbroic rocks; each generation is characterized by different submicroscopic mixtures or solid solutions of sheet silicates: 1) Mg-Fe 2 + lizardite + ferri-lizardite + chlorite, 2) Mg-Fe 2 + lizardite + ferri-lizardite, and 3) Mg-Fe 2 + lizardite + ferri-lizardite + saponite. The first and third generations of serpentine and mixed minerals are relatively Fe-rich, whereas the second generation is Fe-poor and associated with abundant magnetite and pyrrhotite. The major difference between the alteration of gabbroic and peridotitic systems is probably best explained by the iron content and modal abundance of primary olivine and by rock-dominated fluid compositions with a high silica activity due to the alteration of plagioclase in gabbroic rocks. The mineralogical variations between the reported three generations of mixed sheet silicates in gabbroic rocks can be ascribed to variations of silica and/or oxygen activities in the associated fluids under decreasing temperature conditions. The abrupt increase of magnetite crystallization during serpentinization in gabbroic rocks could be caused by oxidation at a relatively high SiO 2 activity without the olivine-serpentine-brucite buffering assemblage. [ABSTRACT FROM AUTHOR]

An association of olivine-gabbroic dikes is located in the northwest of Iran, south-southwest of Germi city (Ardebil province), with N-S trend in the Talesh zone. Mineralogically, these rocks consists of phenocrysts of plagioclase, clinopyroxene (augite) and olivine with minor minerals of biotite, amphibole, apatite, opaque and zircon. The dominant textures in these rocks are porphyry, granular and ophitic. From the chemical aspect, the parent magma is alkaline nature. The spider diagram with a positive lead anomaly indicates the crustal assimilation process with LREE enrichment compared to HREE which is related to enriched mantle. The trend of major oxides vs. SiO2 on Harker diagrams indicates evolution process through differentiation, with slight metasomatism which can be related to subducted slab derived fluid. Based on the aforementioned evidences, the olivine gabbros were formed from an extensional back arc basin resulting from subducting oceanic crust in the northern branch of NeoTethys located between the blocks of Toriid-Anatolli in the south of Armenia beneath the crust of Quafqaz and Armenia. [ABSTRACT FROM AUTHOR]

Zircon SHRIMP U-Pb dating was per- formed for olivine gabbro at Wangmuguan in the Beihuaiyang zone of the Dabie orogen and its country rock (garnet-bearing epidote-mica-quartz schist). The results show that the gabbro was crystallized at 635 ± 5 Ma, in the late Neoproterozoic rather than in the late Paleozoic as previously suggested; its country rocks formed at 464±7 Ma, younger than the enclosed gabbro. The U-Pb age for the gabbro is in good agreement with ages for tuff interbedded with sediments from the Doushantuo Formation in the South China Block and late-Neoproterozoic basic dyke swarms distributed on a large scale over areas of Suizhou to Zaoyang of Hubei Province in the northern margin of the South China Block. This suggests a large-scale magmatic activity occurred at the late Neoproterozoic in the South China Block, so that the gabbro at Wangmuguan in the western segment of the Beihuaiyang zone is geotectonic affinity to the northern margin of the South China Block. Since the olivine gabbro occurs within the schist of Ordovician protolith with tectonic contact between them but forming in different tectonic settings, it is concluded that the late-Neoproterozoic gabbro was detached from the Precambrian basement of the South China Block during the Triassic subduction of the South China Block, and tectonically thrusted over the metamorphosed rocks in the southern margin of the North China Block. [ABSTRACT FROM AUTHOR]

Pressures at which partial crystallization occurs for mid-ocean ridge basalts (MORB) have been examined by a new petrological method that is based on a parameterization of experimental data in the form of projections. Application to a global MORB glass database shows that partial crystallization of olivine + plagioclase + augite ranges from 1 atm to 1·0 GPa, in good agreement with previous determinations, and that there are regional variations that generally correlate with spreading rate. MORB from fast-spreading centers display partial crystallization in the crust at ridge segment centers and in both mantle and crust at ridge terminations. Fracture zones are likely to be regions where magma chambers are absent and where there is enhanced conductive cooling of the lithosphere at depth. MORB from slow-spreading centers display prominent partial crystallization in the mantle, consistent with models of enhanced conductive cooling of the lithosphere and the greater abundance of fracture zones through which they pass. In general, magmas that move through cold mantle experience some partial crystallization, whereas magmas that pass through hot mantle may be comparatively unaffected. Estimated pressures of partial crystallization indicate that the top of the partial melting region is deeper than about 20–35 km below slow-spreading centers and some ridge segment terminations at fast-spreading centers. [ABSTRACT FROM AUTHOR]

To investigate the influence of hydration on brittle deformation of oceanic crustal rocks, we conducted triaxial deformation experiments on gabbroic rocks with various degrees of hydration at a confining pressure of 20 MPa and room temperature, measuring elastic wave velocity. Hydrated olivine gabbros reached a maximum differential stress of 225–350 MPa, which was considerably less than those recorded for gabbros (~450 MPa), but comparable to those for serpentinized ultramafic rocks (250–300 MPa). Elastic wave velocities of hydrated olivine gabbros did not show a marked decrease even prior to failure. This indicated that the deformation of hydrated olivine gabbro is not associated with the opening of the stress-induced cracks that are responsible for dilatancy. Microstructural observations of the samples recovered after deformation showed crack damage to be highly localized to fault zones with no trace of stress-induced crack opening, consistent with the absence of dilatancy. These data suggest that strain localization of hydrated olivine gabbro can be caused by the development of shear cracks in hydrous minerals such as serpentine and chlorite, even when they are present in only small amounts. Our results suggest that the brittle behavior of the oceanic crust may considerably change due to limited hydration. [ABSTRACT FROM AUTHOR]

Isla complex is one of the late Neoproterozoic igneous complexes of the Arabian-Nubian Shield in southern Sinai. This research aims to examine the petrogenesis and tectonic setting of Isla complex, as well as inferring the P-T conditions of the parent magma and the depth of intrusion. A detailed field studies were carried out and representative samples for petrographic and geochemical studies were collected. Chemical analyses of major and trace elements for 18 samples and microprobe analyses for different mineral phases in olivine gabbro were performed. The Isla complex is distinguished into olivine gabbro, diorite and monzonite. The interrelationships between certain oxides and/or oxide ratios point to the important role of fractional crystallization process during the formation of the studied complex and the evolution of its mafic-intermediate rock units. The major fractionated phases were clinopyroxene, amphibole and plagioclase. The analyzed rocks show a gradual decrease in concentration of HFSE from olivine gabbro to monzonite via diorite suggesting overall co-magmatic origin. The low K content in plagioclase and low and constant Y/Nb, Nb/Zr, and K/Nb ratios in gabbroic rock relative diorites and monzonites suggest that during the formation of more evolved rock units, the crustal contamination process became more important. The rock varieties of the Isla complex are fresh and not deformed indicating post-collisional emplacement. The geochemical affinity of Isla complex is analogous to other within-plate post-collisional mafic magmatism of south Sinai. The subduction-related geochemical signature of the examined rocks can be interpreted by partial melting of an enriched lithospheric mantle source following an earlier subduction stage in the ANS. Based on hornblende-plagioclase thermometry, the gabbroic rocks of the Isla complex crystallized at a pressure of 5.5 kbar (~20 km depth), the crystallization temperature was estimated at 823 to 967 °C. The model of lithospheric delamination is supposed to form the studied melt since the delamination of the lithospheric mantle caused the asthenosphere to rise rapidly initiating partial melting and creating the studied gabbroic melt, followed by the fractionation of this melt to form different rock varieties of the Isla complex. The melts then penetrated the crust's base to create the Isla complex in southern Sinai. The estimated age of crystallization and emplacement of the examined complex is < 590–610 Ma, as it invades the old calc-alkaline granites. • The studied Isla complex rock units are olivine gabbro, diorite and monzonite. • Geochemical analysis for major and trace elements were accomplished. • Pyroxene, amphibole, plagioclase and sulfide phases had been chemically analyzed. • An enriched mantle source for the studied mafic intrusions was suggested. • The Isla complex rocks crystallized at a pressure of 5.5 kbar (~20 km depth). [ABSTRACT FROM AUTHOR]

The 1.80–1.76 Ga crystalline basement in Colombia as part of the W-Amazonian Craton is composed mainly of gneisses, granitoids and migmatites, affected later by several compressive and extensional events resulting for example in A-type granites, but also mafic intrusions and dikes. Here we present, after a revision of main geological features, research results obtained on the NW-SE trending ilmenite-apatite-rich Caño Viejita gabbro in the SW-Vichada department some 500 km east of Bogota. Petrographic and geochemical data hint to a metaluminous continental alkaline gabbro enriched in K, Ti and P, possibly due to continental crust reworking or magma mixing, as also confirmed by trace elements characteristics in the apatites like HREE enrichment (Ce/Yb) cn 12–13, negative Eu-anomaly, and Y, Th, Sr, Mn ratios. LA-ICP-MS U–Pb apatite geochronology suggests an early Neoproterozoic emplacement age between 975 ± 9 and 1002 ± 21 Ma related with rifting triggered by the Amazonia-Baltica-Laurentia collision during the Rodinia Supercontinent assembly and associated Grenvillian events. These events also caused mafic intrusions in other parts of the craton. Apatite fission track thermochronometry and thermal history modelling on one sample suggest the onset of the final exhumation stage during Jurassic (~180 Ma), which brought the rocks slowly to their current outcrop position. • LA-ICP-MS U–Pb apatite geochronology as a method for emplacement ages in small intrusions. • Rifting triggered by collisions during the Supercontinent formation. • Mafic intrusions in the W-Amazonian Craton associated to Grenvillian events. • W-Amazonian Craton exhumation stage during Jurassic by Apatite fission track thermochronometry. [ABSTRACT FROM AUTHOR]