Petrological and geochemical characterization of the arc-related Suru–Thasgam ophiolitic slice along the Indus Suture Zone, Ladakh Himalaya

Abstract The Ladakh Himalayan ophiolites preserve remnants of the eastern part of the Neo-Tethyan Ocean, in the form of Dras, Suru Valley, Shergol, Spongtang and Nidar ophiolitic sequences. In Kohistan region of Pakistan, Muslim Bagh, Zhob and Bela ophiolites are considered to be equivalents of Ladakh ophiolites. In western Ladakh, the Suru–Thasgam ophiolitic slice is highly dismembered and consists of peridotites, pyroxenites and gabbros, emplaced as imbricate blocks thrust over the Mesozoic Dras arc complex along the Indus Suture Zone. The Thasgam peridotites are partially serpentinized with relict olivine, orthopyroxene and minor clinopyroxene, as well as serpentine and iron oxide as secondary mineral assemblage. The pyroxenites are dominated by clinopyroxene followed by orthopyroxene with subordinate olivine and spinel. Gabbros are composed of plagioclase and pyroxene (mostly replaced by amphiboles), describing an ophitic to sub-ophitic textural relationship. Geochemically, the studied rock types show sub-alkaline tholeiitic characteristics. The peridotites display nearly flat chondrite-normalized rare earth element (REE) patterns ((La/Yb)N = 0.6–1.5), while fractionated patterns were observed for pyroxenites and gabbros. Multi-element spidergrams for peridotites, pyroxenites and gabbros display subduction-related geochemical characteristics such as enriched large-ion lithophile element (LILE) and depleted high-field-strength element (HFSE) concentrations. In peridotites and pyroxenites, highly magnesian olivine (Fo88.5-89.3 and Fo87.8-89.9, respectively) and clinopyroxene (Mg no. of 93–98 and 90–97, respectively) indicate supra-subduction zone (SSZ) tectonic affinity. Our study suggests that the peridotites epitomize the refractory nature of their protoliths and were later evolved in a subduction environment. Pyroxenites and gabbros appear to be related to the base of the modern intra-oceanic island-arc tholeiitic sequence.

Download Full-text

Geochemical Characterization of Serpentinized Peridotites from the Shergol Ophiolitic Slice along the Indus Suture Zone (ISZ), Ladakh Himalaya, India

The Journal of Geology ◽

10.1086/692653 ◽

2017 ◽

Vol 125 (5) ◽

pp. 501-513 ◽

Cited By ~ 7

Author(s):

Irfan Maqbool Bhat ◽

Talat Ahmad ◽

D. V. Subba Rao

Keyword(s):

Suture Zone ◽

Geochemical Characterization ◽

Ladakh Himalaya

Download Full-text

Serpentinization at the Rainbow and Saldanha sites, Mid-Atlantic Ridge: Mineralogical, geochemical, and isotopic features

The Canadian Mineralogist ◽

10.3749/canmin.1900010 ◽

2019 ◽

Vol 57 (5) ◽

pp. 677-706

Author(s):

Isabel Ribeiro da Costa ◽

Frederick Joseph Wicks ◽

Fernando J.A.S. Barriga

Keyword(s):

Upper Mantle ◽

Hydrothermal Activity ◽

Isotopic Data ◽

Geochemical Characterization ◽

Textural Evolution ◽

Mantle Peridotites ◽

Carbonate Deposition ◽

Mid Atlantic Ridge ◽

Ree Patterns

Abstract The Rainbow hydrothermal field (36°14′N) and the Saldanha seamount (36°34′N), in the Mid-Atlantic Ridge (MAR), are tectonic exposures of serpentinized upper mantle peridotites, both associated with significant hydrothermal activity. On the basis of detailed mineralogical and geochemical characterization of serpentinites from both sites, several serpentinization-related issues are discussed in the present work. As expected in oceanic environments, most of the sampled rocks are lizardite-chrysotile serpentinites exhibiting a variety of pseudomorphic through non-pseudomorphic textures, such textural evolution probably being related to changing water/rock ratios during this retrograde process. Oxygen isotope temperatures indicate that the serpentinization took place at 300–200 °C; on the other hand, isotopic data suggest that replacement of early pseudomorphic lizardite by lizardite ± chrysotile non-pseudomorphic textures requires that temperatures and/or water/rock ratios are high enough to promote the necessary dissolution–recrystallization processes. Mass-balance calculations for olivine-serpentine and orthopyroxene-serpentine pairs provided a basis for establishing serpentinization reactions likely to have produced the present rocks. Moreover, these calculations also showed that, notwithstanding some noticeable loss of MgO from olivine and of SiO2 from orthopyroxene, serpentinization of both minerals implies volume increases on the order of 26–27%, therefore potentially promoting the overall expansion of the rock. The geochemical and isotopic features of the studied rocks indicate that unmodified seawater was responsible for the serpentinization of the MAR peridotites. However, the mineralogy and REE patterns of some of these serpentinites indicate occasional subsequent interaction of the serpentinized rocks with seawater at much lower temperatures (seafloor alteration, characterized by carbonate deposition and negative Ce anomalies), or with high-temperature ore-forming hydrothermal fluids (ore-forming alteration, characterized by sulfide precipitation and steep positive Eu anomalies).

Download Full-text

MINERALOGICAL AND GEOCHEMICAL CHARACTERIZATION OF ZEOLITES IN ALBANIAN OPHIOLITIC PLAGIOGRANITES

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.14105 ◽

2017 ◽

Vol 50 (4) ◽

pp. 1781

Author(s):

E. Goga Beqiraj ◽

F. Muller ◽

A. Beqiraj

Keyword(s):

Secondary Mineral ◽

Geochemical Characterization ◽

The North ◽

Plutonic Complex ◽

Ophiolitic Complex

The plagiogranites, that represent the uppermost part of the plutonic complex of the Albanian ophiolites, are intensively altered. They crop out in the north - easternsectors of the Albanian ophiolitic complex presenting intrusive contacts with volcanic and gabbroic rocks. The zeolite, that is a typically secondary mineral, has filled thin veins and/or small vesicles of the rock. From the XRD, EMPA and microscopic analyses it is concluded that this zeolite belongs to the laumontite - leonhardite (LAU) series.

Download Full-text

Petrography and Geochemical Characterization of a Granite Batholith in Idanre, Southwestern Nigeria

Sains Malaysiana ◽

10.17576/jsm-2021-5002-04 ◽

2021 ◽

Vol 50 (2) ◽

pp. 315-326

Author(s):

Oluwatoyin O. Akinola ◽

Azman A. Ghani ◽

Elvaene James

Keyword(s):

Calc Alkaline ◽

Southwestern Nigeria ◽

Geochemical Characterization ◽

Fine Grained ◽

Rock Types ◽

Pan African ◽

High K ◽

Granite Batholith ◽

Type Granite

Idanre granite batholith in southwestern Nigeria contain three rock types, namely, Older granite undifferentiated (OGu), Older granite porphyritic (OGp) and Older granite fine-grained (OGf). The granitoids intruded into a basement rock of primarily migmatite gneiss. Petrography indicates that quartz, orthoclase, hornblende, and biotite are common to all members while microcline is more prominent in OGp and plagioclase is poorly represented in OGf. Despite minor differences in petrographic features, the granite units generally have similar geochemical relationships. The average SiO2 contents in OGp (70.49%), OGu (68.7%) and OGf (65.8%) are comparable to similar Pan-African suites located in eastern and northern Nigeria. Na2O+K2O-CaO versus SiO2 diagram shows all the granite members are calcic, K2O vs SiO2 plot classify the granites as high-K calcic alkali to shoshonitic. ANK vs ACNK plot indicatesthey are peraluminous. Plot of A/CNK vs SiO2 and K2O vs Na2O diagrams classified the rock as S-type granite. The granitoids are calc-alkaline with elevated Na2O (>2.6%) and Al/(Na2O+CaO) contents (OGu, 2.1-3.4; OGp, 2.4-3.1 and OGf, 2.2-2.9). The tectonic diagram (Rb vs (Y+Nb) indicatesthatthe batholith is Within Plate Granite (WPG.

Download Full-text