Evidence for mantle heterogeneity from platinum-group-element abundances in Indian Ocean basalts

1992 ◽  
Vol 29 (11) ◽  
pp. 2329-2340 ◽  
Author(s):  
Brian J. Fryer ◽  
John D. Greenough
Keyword(s):  
Melting Point ◽  
Indian Ocean ◽  
Noble Metal ◽  
Oceanic Island ◽  
Core Material ◽  
Magma Evolution ◽  
Metal Concentrations ◽  
The Core ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Oceanic-island tholeiitic basalts recovered from four sunken oceanic islands along the Reunion hot-spot trace show trace-element and mineralogical characteristics ranging from typical oceanic-island tholeiites to incompatible-element-depleted tholeiites resembling mid-ocean-ridge basalts. There are also variable degrees of magma evolution at each island. Noble metal (Au, Pd, Pt, Rh, Ru, Ir) abundances tend to decrease with magma evolution and with magma "alkalinity", indicating that the metals behave as compatible elements during crystal fractionation processes and during mantle melting processes. Palladium-to-iridium ratios also decrease with increasing alkalinity. Absolute abundances of elements such as Pd are higher than those in typical mid-ocean-ridge basalts, by factors up to 30, despite many major-element similarities with the latter. Comparison with other types of mafic rocks shows that Pd/Ir ratios increase with decreasing alkalinity in basaltic rocks but plunge to alkali-basalt values in komatiites. A model involving retention of low-melting-point Au, Pd, and Rh in mantle sulphides, which completely dissolve by intermediate percentages of melting, and the high-melting-point metals Ir and Ru in late-melting mantle alloys explains increasing Pd/Ir ratios with decreasing alkalinity (increasing melting percentages) in oceanic basalts and the low Pd/Ir ratios of high-percentage melt komatiites.The high noble metal concentrations in Indian Ocean basalts compared with basalts from many other ocean basins are most easily explained by higher concentrations in their source regions. This may be related to incomplete mixing of a post-core-formation meteoritic component of the upper mantle, or deep mantle plume-derived blebs of core material that either failed to reach the core, during core–mantle differentiation, or were plucked from the core by a convecting lower mantle. The latter is tentatively favoured due to the apparently higher noble metal concentrations in oceanic-island (plume) basalts.

scholarly journals Protolith Oceanic Island Arc dari Granitoid Tipe M dan I di Karangsambung, Kebumen, Jawa Tengah

2019 ◽  
Vol 20 (4) ◽  
pp. 249
Author(s):  
Chusni Ansori ◽  
Shaban Godang ◽  
Defry Hastria ◽  
Isyqi Isyqi
Keyword(s):  
Field Studies ◽  
Oceanic Island ◽  
Island Arc ◽  
Rock Fragments ◽  
Geochemical Study ◽  
Mid Ocean Ridge ◽  
Granitoid Rocks ◽  
Ocean Ridge ◽  
Mantle Magma ◽  
Carbonatite Magma

Granitoid rocks which found at Luk Ulo melange complex as rock fragments with  pale gray colour and faneritic texture. Petrogenesis and geotectonic of the granitoid is under debate. Some geologists consider as plagiogranite, which is formed from the Mid Ocean-ridge (MOR); or leucogranite which is formed from continental collision, and others argue as arc-related granitoid type.The field studies ware carried out on 5 (five) tracks around Luk Ulo River and 1 (one) track at Lokidang River. The pale grey Karangsambung granitoid is composed of the mainly  K-feldspar (34-55%), plagioclase (10-25%) and quartz (25-35%), and chemically contains SiO2 (61.25 - 66.06%); Al2O3 (13.94 – 14.61%), K2O (2.53 - 4.00%), Na2O (3.42 - 4.10%), CaO (2.32 - 4.76%), Fe2O3 total (5.85 – 8.71%), MgO (0.98 – 1.97%). The granitoid is M- and I-type that were formed at 760o - 800o C with a depth of about 20-30 km, resulting from the differentiation of magma from a fragment origin of the K-enriched oceanic island arc originating from drifting of the IAB fragment. The sample of basalt 17D has a relatively high of Nb/Ta ratio (20), low Rb (<2 ppm), low Ba (17 ppm), and is interpreted as interacting with MORB mantle magma containing rutile-melt;whereas quartz monzonite (17A) has a relatively low of Zr/Sm ratio (3.86), which is indicated to have been contaminated by a carbonatite magma. The spidergram pattern of mantle metagabbro (sample no. 13) similar with the basalt from IAB-Bransfield Strait (Antarctica). Results of a comprehensive geochemical study proposes that the current condition of the Karangsambung zone is part of geotectonic of ACM-Eurasia, that composed of a combination of four rock fragments, i.e. (a) the rocks which sourced from IAB fragments, (b) mantle MORB, (c) continental crust from the origin of ACM-Eurasia, (d) the origin fragment from carbonatite magma.Keyword: Luk Ulo Melange Complex, pale grey granitoid, Island-arc granitoid, M  and I-type granitoid

A discussion concerning the floor of the northwest Indian Ocean - The Owen fracture zone and the northern end of the Carlsberg Ridge

1966 ◽  
Vol 259 (1099) ◽  
pp. 172-186 ◽  
Keyword(s):  
Indian Ocean ◽  
Fracture Zone ◽  
Lateral Displacement ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Characteristic Pattern ◽  
Mid Ocean Ridge ◽  
Carlsberg Ridge ◽  
Ocean Ridge ◽  
Transcurrent Faults

Examination of the shape of the earthquake epicentre belt near Socotra led to the suggestion that a major fracture displaces the axis of the mid-ocean ridge in that area (Matthews 1963). Subsequent surveys have confirmed the existence of a fracture zone which extends 1500 miles from the coast near Karachi southwestwards to the middle of the Somali Basin. Linear ridges and troughs in the zone are associated with negative gravity anomalies but not with magnetic anomalies. Where the fracture zone crosses the line of the Carlsberg Ridge a sinuous trough is developed: south of this feature a characteristic pattern of magnetic anomalies is associated with the volcanic structures of the mid-ocean ridge, north of it a line of large non-magnetic seamounts has been found. It is concluded that the structure underlying the Owen fracture zone is a system of parallel transcurrent faults affecting the ocean floor only, at which the axis of the mid-ocean ridge suffers a net right lateral displacement of 170 mi.

scholarly journals The Indian Ocean, its supra-subduction history, and implications for ophiolites

2021 ◽  
Author(s):  
Eldridge M. Moores ◽  
Nathan Simmons ◽  
Asish R. Basu ◽  
Robert T. Gregory
Keyword(s):  
Indian Ocean ◽  
Subduction Zones ◽  
Southern Indian Ocean ◽  
Apparent Paradox ◽  
Midocean Ridges ◽  
Tectonic Environment ◽  
Mid Ocean Ridge ◽  
Forearc Basins ◽  
Back Arc ◽  
Ocean Ridge

ABSTRACT Ophiolite complexes represent fragments of ocean crust and mantle formed at spreading centers and emplaced on land. The setting of their origin, whether at midocean ridges, back-arc basins, or forearc basins has been debated. Geochemical classification of many ophiolite extrusive rocks reflect an approach interpreting their tectonic environment as the same as rocks with similar compositions formed in various modern oceanic settings. This approach has pointed to the formation of many ophiolitic extrusive rocks in a supra-subduction zone (SSZ) environment. Paradoxically, structural and stratigraphic evidence suggests that many apparent SSZ-produced ophiolite complexes are more consistent with mid-ocean ridge settings. Compositions of lavas in the southeastern Indian Ocean resemble those of modern SSZ environments and SSZ ophiolites, although Indian Ocean lavas clearly formed in a mid-ocean ridge setting. These facts suggest that an interpretation of the tectonic environment of ophiolite formation based solely on their geochemistry may be unwarranted. New seismic images revealing extensive Mesozoic subduction zones beneath the southern Indian Ocean provide one mechanism to explain this apparent paradox. Cenozoic mid-ocean-ridge–derived ocean floor throughout the southern Indian Ocean apparently formed above former sites of subduction. Compositional remnants of previously subducted mantle in the upper mantle were involved in generation of mid-ocean ridge lavas. The concept of historical contingency may help resolve the ambiguity on understanding the environment of origin of ophiolites. Many ophiolites with “SSZ” compositions may have formed in a mid-ocean ridge setting such as the southeastern Indian Ocean.

Seafloor topography and tectonic elements of the Western Indian Ocean

2005 ◽  
Vol 363 (1826) ◽  
pp. 15-24 ◽  
Author(s):  
Lindsay M. Parson ◽  
Alan J. Evans
Keyword(s):  
Indian Ocean ◽  
Plate Boundary ◽  
Western Indian Ocean ◽  
Ocean Basin ◽  
Seafloor Topography ◽  
Sedimentary Sequences ◽  
Mid Ocean Ridge ◽  
The Face ◽  
The Indian Ocean ◽  
Ocean Ridge

The break–up of Gondwanaland and dispersal of several of its component continental fragments, which eventually formed the margins of the Indian Ocean, have produced an ocean basin of enormous variety, both in relief and in origin of seafloor features. The western half of the Indian Ocean alone contains every type of tectonic plate boundary, both active and fossil, and, along with some of the deepest fracture zones, the most complex mid–ocean ridge configurations and some of the thickest sedimentary sequences in the world's ocean basins. This ocean is one of the most diverse on the face of the globe. We explore the evolution of the morphology of the Indian Ocean floor, and discuss the effect of its variations, maxima and minima, on the interconnectivity of the ocean's water masses.

Sign in / Sign up

Export Citation Format

Share Document