Search

Globally Cenozoic interval witnessed recurrent climatic change of warming and cooling episodes of various magnitudes. The geological archives of the western part of the Kutch Basin are bestowed with spectacular igneous structures formed during the Deccan Trap volcanism. Overlying, Cenozoic successions of the Kutch Basin also get affected by the global climatic perturbations, which get registered in their impressive stratigraphic successions. Sedimentation in the basin was primarily controlled by the rate of relative sea-level fluctuations vs. background siliciclastic supply. Combined effect of climatic perturbations and relative sea-level fluctuation along passive-margin setting resulted in the occurence of variety of fossils, lithology and sedimentary structures, available all over the Cenozoic outcrops. To conserve and protect endangered geological features, geoscientists around the world have recognized several geosites, which can serve as standard reference section for further research and sustainable development for generations. In this study, we identify some spectacular outcrops from the western parts of the Kutch Basin (Cenozoic outcrops and Deccan Trap exposures) and document their properties to be recognized as potential geosites. These sites preserve exclusive geological features and provide template to understand the geological processes, however, needs conservation and protection. We propose the following assorted geosites viz. (1) Entablature geosite, (2) Pillow lava geosite, (3) Taphonomy geosite, (4) Fossil crab geosite, (5) Trace fossil geosite and (6) Soft sediment deformation (SSD) geosite. These sites may serve as exclusive locations for students field excursion, field-training for diverse professionals, social outreach activities and future reference section; indeed helps to achieve the implementation of some of the geoheritage goals. Diverse and unique geological features can be easily approached by thoroughly connected rail network and metalled roads. [ABSTRACT FROM AUTHOR]

As a part of the Kermanshah ophiolite in western Iran, the Cretaceous Nourabad-Dinavar ophiolitic complex is a remnant of the Neo-Tethys oceanic lithosphere and represents transitional mantle-crust and upper crust units in the Nourabad and Dinavar regions, respectively. All the units were affected by the two metamorphic regimes of static metamorphism and dynamic metamorphism. The whole-rock chemical data of the basic samples (i.e. gabbros, basalts, and dykes) show that they are related to the island-arc regime. The main reasons for this conclusion are as follows: their affinity with the calc-alkaline series, LREE enrichment, and subduction-related proxies such as the negative anomalies of Nb, Ta, Zr, and Hf and the positive anomaly of Th. On the other hand, the mineral chemistry analysis confirms that the studied ophiolitic complex is a MORB-type ophiolite emplaced in the supra-subduction zone. This is supported by mineralogical evidence including the compositional dependence of olivines (fo90-91) on the spinel peridotite mantle facies, spinel minerals (Al-chromite and Mg/Cr-bearing hercynite), and Mg-rich orthopyroxenes (enstatite) in the harzburgites. The geochemical modeling implies that this complex evolved through the following successive magmatic steps: 1) the partial melting of a mixed NMORB-EMORB (50:50) source producing spinel harzburgite residues; 2) the fractional crystallization of the basic partial melts during their ascent to the surface and the formation of gabbro bodies; 3) the assimilation and fractional crystallization process as the NMORB components re-enter the chamber and produce basic pillow lavas, lava flows, and some fine-grained gabbro bodies (i.e. dykes). Accordingly, it can be interpreted that the emplacement history of the studied ophiolite succession has two stages: 1) an obduction stage in the Campanian; 2) an exhumation stage in the post-Cretaceous. [ABSTRACT FROM AUTHOR]

Paleomagnetism has played a crucial role in unraveling processes such as plate motion and the emplacement of volcanic products. Despite its significance, a full range of such studies have not been possible for samples from the oceans, primarily due to the technical obstacles associated with obtaining oriented samples from the seafloor. Here we devised a rapid and uncomplicated technique for collecting oriented samples from the seafloor utilizing a cross-line laser system installed on the biaxial pan-tilt unit of the human occupied vehicle (HOV) SHINKAI 6500. This system comprises one laser capable of projecting a vertical line with horizontal mobility, together with a second laser positioned perpendicular to the vertically oriented beam, allowing flexibility to adjust its projection both upward and downward. The center of the cross-line laser is focused on a target rock or sediment corer. Orientation of the cross-line laser is calculated from the positions of SHINKAI 6500 and the pan-tilt unit, which are recorded every second. An accurate restoration of the collected sample to its original orientation can be achieved based on the laser path marked on the rock surface and the laser orientation data. We collected rocks and sediments from the seafloor of the Okinawa Trough in order to test our new orientation method and conducted paleomagnetic measurements on them. Paleomagnetic directions of the rocks are roughly consistent with the Earth's current magnetic field direction, proving validity of the method. This innovative method has the potential to become widely adopted for collecting oriented samples from seafloor using a HOV and remotely operated vehicle (ROV). • We invented a new technique for collecting oriented samples from the seafloor. • The cross-line laser system installed on the submersible SHINKAI 6500 is used. • Oriented rocks and sediments were collected from the seafloor of the Okinawa Trough. • Paleomagnetic directions of the rocks proves validity of the method. [ABSTRACT FROM AUTHOR]

We report on the occurrence of pillow lava in the upper part of the banded‐iron‐formation (BIF) sequence of the Quadrilátero Ferrífero, famous for hosting world‐class iron‐ore deposits in Minas Gerais, Brazil. A pillow‐lava domain is found as an outlier within the BIF sequence, known as the Itabira iron formation or the Itabira Group. The pillow lava occurs as lateritized, indurated crusts in a sequence of ochreous itabirite, the weathered expression of dolomitic itabirite, a metamorphosed BIF rock containing dolomite. About 90 zircon grains, extracted from two samples of lateritized pillow lava, an indurated pillow rim and a friable pillow core, yielded Archaean to Palaeoproterozoic ages between 3.37 and 2.14 Ga, with age clusters at 2.98, 2.72, 2.25, and 2.14 Ga, and minor clusters at 3.37, 3.26, 3.16, and 2.82 Ga. The youngest grains, all exhibiting perfectly euhedral crystals, defined a Concordia age at 2,141 ± 6 Ma, interpreted as the age of subaqueous volcanism. This young zircon age and the perfectly euhedral zircon crystals suggest that the pillow‐lava domain represents an outlier of Palaeoproterozoic volcanic rocks, which covered the unconformity between the Itabira Group and the overlying Piracicaba Group. The finding of pillow lava lends support to previous, but usually ignored works, which described metavolcanic rocks in spatial association with the Itabira Group, and provides evidence for subaqueous volcanism that challenges the prevailing view of a stable‐shelf or passive‐margin setting for the geological evolution of the Minas Supergroup. [ABSTRACT FROM AUTHOR]

Abstract Subduction‐related lavas have higher Fe3+/∑Fe than midocean ridge basalts (MORB). Hypotheses for this offset include imprint from subducting slabs and differentiation in thickened crust. These ideas are readily tested through examination of the time‐dependent evolution of slab‐derived signatures, thickening crust of the overriding plate, and evolving redox during subduction initiation. Here, we present Fe3+/ΣFe and volatile element abundances of volcanic glasses recovered from International Ocean Discovery Program (IODP) Expedition 352 to the Izu‐Bonin‐Mariana (IBM) forearc. The samples include forearc basalts (FAB) that are stratigraphically overlain by low‐ and high‐silica boninite lavas. The FAB glasses have 0.18–0.85 wt% H2O, 75–233 ppm CO2, S contents controlled by saturation with a sulfide phase (602–1,386 ppm), Ba/La from 3.9‐10, and Fe3+/ΣFe ratios from 0.136 to 0.177. These compositions are similar to MORB and suggest that decompression melting of dry and reduced mantle dominates the earliest stages of subduction initiation. Low‐ and high‐silica boninite glasses have 1.51–3.19 wt% H2O, CO2 below detection, S contents below those required for sulfide saturation (5–235 ppm), Ba/La from 11 to 29, and Fe3+/∑Fe from 0.181 to 0.225. The compositions are broadly similar to modern arc lavas in the IBM arc. These data demonstrate that the establishment of fluid‐fluxed melting of the mantle, which occurs in just 0.6–1.2 my after subduction initiation, is synchronous with the production of oxidized, mantle‐derived magmas. The coherence of high Fe3+/∑Fe and Ba/La ratios with high H2O contents in Expedition 352 glasses and the modern IBM arc rocks strongly links the production of oxidized arc magmas to signatures of slab dehydration.

The Upper Cretaceous Arangue complex is located in the Makran zone at the SE of Iran. The complex consists of ultra-mafic rocks, microgabbro dykes, pillow lavas and lime stones that pillow lavas are mainly exposed to the northwest and southeast part of study area. There are oval and tubular basalt lavas with cracked bread crust surface. They predominantly have plagioclase, clinopyroxene with minor olivine and opaque minerals in a fine-grained groundmass along with glass. Mineral chemistry data show that plagioclases and clinopyroxene composition varies from An68.27-81.73 Ab18.27-31.57 Or0- 0.41 and Wo38.1- 47.8Fs8.2-19.3 En38.6-48.7 respectively. In the geochemical diagrams, the Arangue complex pillow lavas fall in the basalt and sub-alkaline fields. Geochemical data indicate that the Arangue complex pillow lavas are tholeiitic. The absence of a distinct Eu anomaly (Eu/Eu*= 0.8-1.2), indicates that plagioclase fractionation is not notable, or that the magma is a little oxidized. The Arangue complex pillow lavas show properties similar to transitional basalts between enriched MORB and OIB and some BABB. However, their enrichment in incompatible elements and low Nb and La / Nb ratios (0.8-2.1) display that these have affinity of the BABB. These were produced by approximately 15-25% partial melting of plagioclase lherzolite where fractionation was controlled by removal of clinopyroxene, spinel, and olivine. Petrogenetic study indicates that the source of mantle lherzolite is subjected to enrichment variables in subduction components consisting of fluids for the Arangue Complex pillow lavas. [ABSTRACT FROM AUTHOR]

Ophiolites, found in orogenic belts, are slices of ancient oceanic lithosphere obducted on land during continental collision and ocean closure. They provide valuable insights into submarine volcanological and petrological processes. Palaeotectonic interpretations of ophiolites have heavily depended on geochemical data, despite the considerable submarine alteration and even metamorphism commonly observed in ophiolites. No independent checks on the geochemistry-based inferences are usually provided or sought. Here, we present a hitherto unavailable volcanic facies perspective on the ~ 140 Ma Nidar ophiolite, exposed > 4100 m above sea level in the Ladakh region of the Indian Trans-Himalaya. We describe features of pillow lavas and hyaloclastite forming the oceanic crust and of peperite and silicic volcanic ash layers in the overlying sedimentary cover (mainly radiolarian cherts, dated at 132–112 Ma). The whole volcanosedimentary sequence is inconsistent with a mid-ocean ridge setting. We interpret it as having formed in a shallow (~ 2.5 km) submarine environment, with ongoing explosive silicic eruptions, in an Early Cretaceous, compositionally bimodal, intra-oceanic island arc in the Neo-Tethys Ocean. Geochemical-isotopic data on the Nidar ophiolite have previously been used to argue for an intra-oceanic arc origin. We suggest that a volcanic facies approach to the study of ophiolites can be a valuable guide to their palaeodepths and palaeotectonic settings. [ABSTRACT FROM AUTHOR]

The amorphous carbonaceous material (CM) in mafic igneous rocks is important for deciphering the relationships between igneous and hydrocarbon systems in Earth interior. Deciphering of CM in Precambrian rocks it is a challenge because of reworking by later superimposed events but could give insights into evolution of these systems in time. We report the results of combined field and petrological studies, Raman spectroscopy and carbon isotope analysis of well-preserved ca. 2.0 Ga pillow lavas in the Onega Basin, Karelian craton, Eastern Fennoscandian Shield. In these rocks CM is present in both pillow and inter-pillow areas as poorly ordered carbon. In the MORB-like basalts of the Zaonega Formation, CM occurs in post-magmatic veinlets formed via migration of hydrothermal fluids. In the OIB-type basalts of the Suissary Formation, CM is found in amygdales, inclusions in feldspar, and in devitrified volcanic glass indicating a CM deposition via a rapid cooling of C-rich magma. Despite morphological diversity carbon isotopic composition indicates a biogenic origin of CM in both the MORB- and OIB-like basalts. The most likely source was the Paleoproterozoic oilfield in the Zaonega Formation, commonly referred to as the Shunga event. • Paleoproterozoic basaltic pillow lavas contain up to 6 wt. % of amorphous carbonaceous material in two textural positions. • In groundmass, microliths and amygdales, amorphous carbonaceous material was deposited from the melt during the lava cooling. • In post-solidification veins of the lavas, amorphous carbonaceous material was precipitated from hydrothermal fluids. • δ13C org signatures indicate origin of the carbonaceous material from a single source, ca. 2.0 Ga oilfield within the Paleoproterozoic Zaonega Formation. [ABSTRACT FROM AUTHOR]

Abstract: The study of volcanogenic and volcanogenic-sedimentary rocks (Early Proterozoic pillow lava of Karelia and South Africa), where diverse fossilized bacteria (prokaryotes) and probably even eukaryotes shows that, during this early period, conditions of cooling lava flows and igneous rocks were favorable for bacterial development and colonization. [ABSTRACT FROM AUTHOR]

Field, petrological and mineral chemistry for meta-volcanic rocks from the Aravalli sequence (Aravalli Craton, India) are presented. Field evidence such as volcanic flows and suspect pillow lava structures, dominant Fe-tholeiite lava flows intercalated with quartzites and argillaceous sediments, indicate rift tectonic environment. Primary mineralogy was obliterated during post-magmatic processes such as metamorphism corresponding to the greenschist to lower amphibolite facies conditions. The rock’s mineral composition was overprinted by plagioclase–chlorite–amphibole–epidote assemblage. The relicts of clinopyroxene were observed. The P-T estimation indicates a temperature of 550–600 °C for the pressure ranging from 3.0 to 7.0 kbar for the majority of amphiboles and 8.0–10.7 kbar for the minority. Geochemically, these rocks are komatiitic (picritic) and high-Fe tholeiitic basalts with 45.06−59.2 wt.% SiO2 and MgO content from 5 to 22.4 wt.% and Mg# of 17 to 71. They show large-ion lithophile elements (LILE) and light rare-earth elements (LREE) enrichment. Chondrite normalized rare-earth elements (REE) patterns for the Aravalli lava are moderately enriched with (La/Sm)N = 1.1−3.85, (La/Yb)N from 1.49 (komatiites) to 14.91 (komatiitic basalts). The trace element systematics with the negative Nb, P and Zr anomalies reflect their derivation from enriched sub-continental lithospheric sources, although minor crustal contamination cannot be ruled out. Aravalli rocks are considered to represent the transition from continental rift magmatism to shallow submarine eruption.

The Eocene subaqueous volcanic units in NE Turkey developed as pillow, closely packed pillow, isolated pillow, pillow breccia, hyaloclastite breccia and rare peperitic facies with red micritic limestones. They are locally set on volcaniclastic sandstone and claystone alternations and gradually pass to tuffs and volcanic breccias. The pillow lava samples generally exhibit intersertal, intergranular, microlitic porphyritic, variolitic, vesicular and glomeroporphyritic and glassy textures with clinopyroxene (Wo 47-52 En 40-45 Fs 6-8 ), plagioclase (An 10 to An 96 ), olivine (Fo 79-87 ) and Fe-Ti oxides (Usp 0-0.27 ). Saponite, interlayered chlorite/saponite, rare beidellite and calcite were determined after olivine, rarely after plagioclase as well as in the glassy groundmass. Illite was restricted to plagioclase and the glassy groundmass. Na-Ca zeolites, chlorites/saponites, beidellite, dolomite and calcite occur as void infillings and in the glassy groundmass. Mineralogical, lithochemical and isotopic interpretations as well as thermometric calculations reveal a low-temperature seawater alteration in a semi-closed environment for the alteration of primary minerals and volcanic glass in addition to sealed vesicles and open systems for crosscutting veins. Due to the short exposure time intervals of seawater to rocks, the total chemistry of the rocks is not fully changed and most of the elements seem to be immobile, remaining in the system as a result of precipitation in voids and cracks. Thermometric estimations indicate that, the temperature of heated seawater is approximately 160 °C at the highest point especially in the vesicles, and decreases to approximately 85 °C due to circulation, resulting in alterations of the primary phases and volcanic glass. [ABSTRACT FROM AUTHOR]

http://dx.doi.org/10.17014/ijog.vol3no1.20084This paper discusses the study on the basalt volcanic rocks and the volcano morphology indicating the existence of an ancient submarine volcano in Tawangsari-Jomboran sub-regency, Sukoharjo- Wonogiri, Central Java. In general, this basalt volcanic rocks were identified as andesite breccia which might be grouped into the Mandalika Formation of Oligosen-Miosen age (Surono et al., 1992). The origin of the Mandalika Formation in relation to the classic sedimentation process and the submarine volcanism is still needed to be evaluated. The present study was based on the detailed descriptions of the rocks both in the field and in the laboratory. The autoclastic basalt outcrops consisting of breccias show the characteristics of the igneous rock fragment component embedded in the groundmass with the same composition, namely igneous rock, dark grey to black in colour; porphyritic texture, rough surface, brecciated; pillow structures, massive, fine vesicularities, amygdaloidal filled with calcite, and radial fractures; calk-alkaline andesite composition ( SiO = 54.71% , K O = 1.15% ). This rock body attains the dimension of 2 - 5 m length, and 40 cm - 1 m in diameter with the direction of the deposition varies following the direction of the eruption source. Brecciated structures on the surface was controlled by the high cooling rate and the low flow, while the interior of the rock is massive because it was not in a direct contact to the cooler mass outside. Autoclastic basalt breccias and or the pillow basalt lava was interpreted to be formed by the undulating low gradient of morphology with the average angle of o. On the other hand, the low basaltic magma viscosity produced the effusive eruption related to the formation of the low angle morphology. The distance between the hills generally composed of pillow basalt is between 500 m - 1 km. The typical pillow structure of the igneous rock as described above is interpreted to be the product of the lava flow related to the effusive eruption from a submarine volcano located under or close to the seawater surface.

http://dx.doi.org/10.17014/ijog.vol3no4.20081Lithologically, the Nampurejo Pillow Lava, Kebo and Butak Formations, which are dominated by volcanic rocks, spread west - eastly, along the northern foot of the Baturagung Mountains. The Nampurejo Pillow Lava, which has an Early Oligocene age, is overlain by the Late Oligocene - Early Miocene Kebo and Butak Formations successively. The Nampurejo Pillow Lava consists of basaltic pillow-lavas showing pillow structures and they are intercalated by black sandstones. The Kebo Formation comprises alternating sandstone and pebbly sandstone with intercalations of siltstone, claystone, tuff, and shale. On the other hand, the Butak For- mation is composed of polymic breccia with intercalations of sandstone, pebbly sandstone, claystone, and siltstone/shale. The three units were deposited in a deep – shallow marine basin, which was filled by volcanic prod- ucts. Compared to the lower part of the Kebo Formation, volcanic activities during the deposition of the upper part of the Kebo Formation and the Butak Formation were more active.

http://dx.doi.org/10.17014/ijog.vol3no3.20081Pillow lava flows of pyroxene basalt containing 50 wt.% SiO are exposed at Opak River, west of Watuadeg Village, Sleman - Yogyakarta. The length of flow structures is between 2 – 10 m, with diameter of 0.5 – 1.0 m and it has a glassy skin at the surface body. Flow directions vary from N70E in the northern side, through N 120E in the middle to N 150E in the southern side. About 150 m away from the river to the west, there is a small hill about 15 m high, that has a similar composition with the pillow lavas. Both lava flows and the small hill are composed of pyroxene basalt, dark grey in color, hypocrystalline vitrophyre to porphyritic texture, with fine-grained phenocrysts of pyroxene (10 %) and plagioclase (25 %) set in glassy groundmass. These data indicate that the small hill was the eruption source of the basaltic pillow lavas. The lavas are overlain by pumice-rich volcaniclastic rocks, composed of tuff, lapillistones and pumice breccias, that are known as the Semilir Formation. Near the contact with lavas, the volcaniclastic rocks contain some fragments of pyroxene basalt, similar composition with the pillow lavas. This fact, together with analyses of petrology, volcanology, and radiometric dating show that the basaltic pillow lavas are unconformably overlain by the Semilir Formation.

The eclogites exposed along northeastern boundary of the Belomorian orogen in the eastern Fennoscandian Shield were formed as a result of Mesoarchean–Neoarchean subduction and collision. As has been shown previously, the common protolith of the Salma-type subduction-related eclogite was oceanic layered gabbro. In this paper, we characterize eclogites formed from volcanic–sedimentary rocks of the upper oceanic crust, which comprised pillow lavas and associated aluminous sediments that filled the interpillow space intercalated with lava flows. As a result of eclogite facies metamorphism, the aluminous sediments have been transformed into coarse-grained garnet–phengite–quartz rocks under pressure no lower than 21 kbar at a temperature of ~650 °C. Alternatively, we cannot rule out the possibility that the garnet–phengite–quartz veins represent solidified felsic melts that were produced by melting of boron-bearing hydrothermally altered oceanic crust in the subduction zone. During transfer to the upper crust under high-P granulite facies conditions, phengite underwent incongruent melting with formation of complex polymineralic pseudomorphs consisting of feldspar, biotite, muscovite and kyanite with corundum and dumortierite. The peak of high-T metamorphism during exhumation of the eclogites is estimated at 850–900 °C, i.e. at least 50–100 °C higher than previous estimates. [ABSTRACT FROM AUTHOR]