Dunite may also form by the accumulation of olivine crystals on the floor of large basaltic or picritic magma chambers. It is thus probable that highly serpentinized peridotites are down. Compositional signatures of ssztype peridotites from the. The mantle and crustal evolution of two garnet peridotite suites from the western gneiss region, norwegian caledonides. I bought this book for a friend of mine that grew up in san luis obispo, ca.
Veins, dikes, and pods of the uae mantle peridotites. Magnetic properties of serpentinized peridotites from the dongbo. Serpentinized peridotites were already sampled at a. Peridotites from the izuboninmariana forearc odp leg. Previous studies have suggested that the garnet peridotites represent alaskanstyle magmatic cumulates or oceanic serpentinites that were subducted to depths of 200km. Its a similar situation if i write vegetables and fruits and it is changed to vegetables, apples and fruits. Mineralogy and geochemistry of peridotites and chromitites in the.
It has been interpreted as an ophiolitic massif derived from the. I wrote peridotites, pyroxenites but it was expanded to peridotites, dunites and pyroxenites. Pdf the mantle and crustal evolution of two garnet. Magnetic properties of serpentinized peridotites from the. Geochemistry and tectonic significance of peridotites from. The mantle peridotites collected from the typical ibm forearc seamounts torishima forearc, conical, and south chamorro seamount have similar geochemical compositions to those from the hahajima. Here, we present petrological data on a forearc peridotite suite obtained as xenoliths in an alkali basalt dike 7. Peridotite is ultramafic, as the rock contains less than 45% silica. Therefore, the s 60% and s 2030% serpentinized peridotites represent the most magnetic rocks in the dongbo ophiolite, and peridotites with such degrees of serpentinization are most likely the sources of the large. Dunites from conical seamount have much higher ferric iron contents than their spatially related harzburgites, with fe 2 o 3 contents up to 4. Geochemistry of serpentinized peridotites from the mariana.
Iron isotopic constraints on the origin of peridotite and. Peridotite, a coarsegrained, darkcoloured, heavy, intrusive igneous rock that contains at least 10 percent olivine, other iron and magnesiarich minerals generally pyroxenes, and not more than 10 percent feldspar. Peridotites can also form as cumulates in layered intrusions, peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of pyroxenes, chromite, plagioclase, and amphibole. Abyssal and suprasubduction peridotites in the lajishan. Typical peridotite sample dunite, left and large olivine crystal right. Lithology and petrologic nature of the forearc mantle have been left unclear due to the very limited sampling to date. One of these days i might get the chance to read it. Archean middle proterozoic more than 1ga and upper proterozoic about 600 ma which is associated with the formation of dunites and chromitites. The northern extension of the semail ophiolite in the uae is dominated by tectonic mantle peridotites and gabbros.
Evaluation of ultramafic deposits in the eastern united states and. Petrology of the yugu peridotites in the gyeonggi massif. These include lherzolite, harzburgite, dunite, wehrlite, and kimberlite see photos. The host alkali basalt is of asthenosphere origin, and. Both dunites and harzburgites in this area preserve lattice preferred orientations in olivine, with a strong a axis lineation plunging gently to the nnw miller and mogk, 1987. Most tabular dunites have a nw strike, with steep dips as mentioned above. Spatial distribution of melt conduits in the mantle. Citeseerx peridotites from the izuboninmariana forearc. Diamonds were found together with chromospinel, moissanite, graphite, zircon, corundum, garnets. The lowal opx in the luobasa dunites has been attributed to the reaction of boninitic melts with the surrounding peridotites zhou et al. These deposits are coexistent with the blue ridge mountains, and outcrop in a belt about 300 miles long.
Petrogenesis of highly depleted peridotites and gabbroic rocks from the mayaribaracoa ophiolitic belt eastern cuba article pdf available in contributions to mineralogy and petrology 1516. The chromite occurrences are hosted in the mantle peridotites. Formation of podiform dunites in the lycian peridotite. Great overview of the mix of eccentric characters who made up this dunelandscape community of individuals. We have implemented such a study using olivinespinel diffusivity patterns in fresh mineralogical samples from the finero maficultramafic complex in the ivreaverbano zone of northern italy. The samples are identified by sequential numbers for simplicity.
Ultramafic rocks peridotites, dunites, pyroxenites occur at the base of the stillwater and bushveld complexes, and are overlain by a variety of norites, troctolites, gabbros, and anorthosites. Implications for the elemental recycling at subduction zones. Magnetic properties of a suite of variably serpentinized peridotites from the dongbo ophiolite, sw. A very limited amount of gabbroic lithologies 1 kg in total were recovered at the scc and ccc, limited to small intrusions within mantle peridotites. If the address matches an existing account you will receive an email with instructions to reset your password. Postdepletion metasomatism of both rock types is indicated by variable enrichment in the light rare earth elements, th, ba and sr. Peridotite is a dense, coarsegrained igneous rock consisting mostly of the minerals olivine and. These rocks have been chosen to test a new magnetic fabric based on measuring the anisotropy of magnetic susceptibility ams in highfield with a vibrating sample magnetometer. The errotobbio et peridotite in the ligurian alps of n italy represents the mantle section of the voltri massif, the largest ophiolite exposure in the european alps. Problem is that dunite is already one of peridotites. In the rocks shown below, the greenish material is forsterite olivine magnesiumrich mg,fe 2 sio 4.
The dongbo peridotites in this study consist of five dunite samples and 28 harzburgite samples. Pdf peridotites from the izuboninmariana forearc odp. The northern vourinos peridotites are spinel peridotites, containing neither plagioclase nor garnet, being derived from the spinel stability field in the mantle, which lies in a. Peridotites exposed in the yugu area in the gyeonggi massif, south korea, near the boundary with the okcheon belt, exhibit mylonitic to strongly porphyroclastic textures, and are mostly spinel lherzolites. Dunites are 90% olivine varieties of peridotites, which are ultramafic intrusive igneous rocks. Textures of plutonic rocks university of washington. Compositional heterogeneity and melt transport in mantle. Amphibole is found in some of the peridotites but rarely exceeds 1% of the mode. The effects of pressure, water and differential stress on the crystallographic preferred orientation cpo of olivine were investigated by an integrated study on peridotite samples from four areas.
Our analytical suite includes chromitites and dunites of the. Zlatogorsk, aiyrtau, north kazakhstan region, kazakhstan. Other minerals that coexist with olivine are lowca orthopyroxene opx, highca clinopyroxene cpx, and chromian spinel always present in very low modal abundance. The compositions of peridotites from these layered igneous complexes vary widely, reflecting the relative proportions of. He sent me an article that was written in the local newspaper about these people called the dunites that lived in the pismo beach dunes in the 1930s i think. The northern vourinos peridotites are spinel peridotites, containing neither plagioclase nor garnet, being derived from the spinel stability field in the mantle, which lies in a p range between 0. Peridotite is a dense, coarsegrained igneous rock consisting mostly of the minerals olivine and pyroxene. This ophiolite includes serpentinized peridotites, harzburgites, dunites, gabbros, sheeted dykes, pillow lavas and mudstones. Reos isotopic data provide new constraints on the origin and formation of the peridotites. The fe isotope variations of the minerals together with petrological features and major elemental compositions, suggest a residual origin for the harzburgites and an accumulation process associated with the dunite. The peridotites are mostly harzburgite with little lherzolites and contain various intermittent veins, dikes, and pods. Crspinels from alyki indicate a moderate fertile character and are analogous to those from abyssal peridotites. The dunites by norman hammond goodreads share book.
The day book dunite of western north carolina appears to. Citeseerx transformation of archaean lithospheric mantle. Along with these, the results of upb dating of zircons from. According to the iugs classification le bas and streckeisen, 1991, they are defined as a coarsegrained ultramafic rock type, containing more than 40 % olivine. The day book dunite of western north carolina appears to represent a metamorphosed sliver of mantle rocks, but it has not been serpentinized. Global variations in abyssal peridotite compositions sciencedirect. The cumulative dunites were formed via crystal cumulation from mantle magmas and. The preoceanic evolution of the errotobbio peridotite. Peridotites are the main lithology of the earths upper mantle. Its peridotites consist of spinel harzburgites, dunites and chromitites. The data demonstrate that the harzburgites originated as the residue from melting at a ridge probably the early east scotia sea spreading centre, and were subsequently modified to transitional peridotites and dunites by interaction with south sandwich arc magmas.
Cumulate peridotites often have cumulate textures and exhibit preferred crystal orientation. The spinel group minerals in the ore and in ultramafic samples were sampled in seven different chromite mines y. Geosciences free fulltext petrogenetic implications for ophiolite. Peridotites usually contain olivine as their primary mineral, frequently with. The twin sisters dunite massif, washington state, provides unweathered peridotites for magnetic analysis. Petrology of peridotites and related gabbroic rocks around the. Harzburgites and serpentinized dunites are characterized by ushaped rare earth element patterns and low pdgroup platinumgroup elements resembling the geochemical features of suprasubduction peridotites.
Petrogenesis of highly depleted peridotites and gabbroic. Geochemistry of serpentinized peridotites from the mariana forearc conical seamount, odp leg 125. The fe isotope variations of the minerals together with petrological features and major elemental compositions, suggest a residual origin for the harzburgites and an accumulation process associated with the dunite formation. The most dramatic examples of this are the dunite channels that form during reactive melt flow in the shallow upper mantle kelemen et al. Odp leg 125 recovered serpentinized harzburgites and dunites from three sites on the crests and flanks of the active conical seamount. These differences are examined more closely in the section on oxygen fugacity. Petrogenesis of dunitetroctolite from the uraniwa hills will be shown in a separate paper. Mantle peridotites harzburgites to dunites are abundant in the ccc, whereas only gabbroic rocks were collected at the ncc. These cumulate dunites typically occur in thick layers in layered intrusions, associated with cumulate layers of wehrlite, olivine pyroxenite, harzburgite, and even chromitite a.
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