Partial Melting of the Lower Oceanic Crust: Implications for Tracing the Slab Component in the Source of Mid‐Ocean Ridge Basalts

2020 ◽  
Vol 125 (10) ◽  
Author(s):  
Yu Wang ◽  
Yigang Xu
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Mid Ocean Ridge ◽  
Ocean Ridge ◽  
Lower Oceanic Crust

scholarly journals Reaction Between Mid‐Ocean Ridge Basalt and Lower Oceanic Crust: An Experimental Study

2019 ◽  
Vol 20 (9) ◽  
pp. 4390-4407 ◽  
Author(s):  
Alexandra Yang Yang ◽  
Chunguang Wang ◽  
Yan Liang ◽  
C. Johan Lissenberg
Keyword(s):  
Experimental Study ◽  
Oceanic Crust ◽  
Ridge Basalt ◽  
Mid Ocean Ridge ◽  
Ocean Ridge ◽  
Lower Oceanic Crust

scholarly journals Partial Melting of Lower Oceanic Crust Gabbro: Constraints From Poikilitic Clinopyroxene Primocrysts

2018 ◽  
Vol 6 ◽  
Author(s):  
Julien Leuthold ◽  
C. Johan Lissenberg ◽  
Brian O'Driscoll ◽  
Ozge Karakas ◽  
Trevor Falloon ◽  
...  
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Lower Oceanic Crust

Platinum-group element geochemistry of intraplate basalts from the Aleppo Plateau, NW Syria

2012 ◽  
Vol 150 (3) ◽  
pp. 497-508 ◽  
Author(s):  
GEORGE S.-K. MA ◽  
JOHN MALPAS ◽  
JIAN-FENG GAO ◽  
KUO-LUNG WANG ◽  
LIANG QI ◽  
...  
Keyword(s):  
Partial Melting ◽  
Middle Miocene ◽  
Primitive Mantle ◽  
Element Geochemistry ◽  
Alkali Basalts ◽  
Melt Extraction ◽  
Mid Ocean Ridge ◽  
Order Of Magnitude ◽  
Platinum Group ◽  
Ocean Ridge

AbstractEarly–Middle Miocene intraplate basalts from the Aleppo Plateau, NW Syria have been analysed for their platinum-group elements (PGEs). They contain extremely low PGE abundances, comparable with most alkali basalts, such as those from Hawaii, and mid-ocean ridge basalts. The low abundances, together with high Pd/Ir, Pt/Ir, Ni/Ir, Cu/Pd, Y/Pt and Cu/Zr are consistent with sulphide fractionation, which likely occurred during partial melting and melt extraction within the mantle. Some of the basalts are too depleted in PGEs to be explained solely by partial melting of a primitive mantle-like source. Such ultra-low PGE abundances, however, are possible if the source contains some mafic lithologies. Many of the basalts also exhibit suprachondritic Pd/Pt ratios of up to an order of magnitude higher than primitive mantle and chondrite, an increase too high to be attributable to fractionation of spinel and silicate minerals alone. The elevated Pd/Pt, associated with a decrease in Pt but not Ir and Ru, are also inconsistent with removal of Pt-bearing PGE minerals or alloys, which should have concurrently lowered Pt, Ir and Ru. In contrast, melting of a metasomatized source comprising sulphides whose Pt and to a lesser extent Rh were selectively mobilized through interaction with silicate melts, may provide an explanation.

scholarly journals Lithogeochemistry of the Mid-Ocean Ridge Basalts near the Fossil Ridge of the Southwest Sub-Basin, South China Sea

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 465 ◽  
Author(s):  
Kai Sun ◽  
Tao Wu ◽  
Xuesong Liu ◽  
Xue-Gang Chen ◽  
Chun-Feng Li
Keyword(s):  
South China Sea ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
South China ◽  
Spreading Rate ◽  
Tholeiitic Basalt ◽  
Spinel Peridotite ◽  
China Sea ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

Mid-ocean ridge basalts (MORB) in the South China Sea (SCS) record deep crust-mantle processes during seafloor spreading. We conducted a petrological and geochemical study on the MORBs obtained from the southwest sub-basin of the SCS at site U1433 and U1434 of the International Ocean Discovery Program (IODP) Expedition 349. Results show that MORBs at IODP site U1433 and U1434 are unaffected by seawater alteration, and all U1433 and the bulk of U1434 rocks belong to the sub-alkaline low-potassium tholeiitic basalt series. Samples collected from site U1433 and U1434 are enriched mid-ocean ridge basalts (E-MORBs), and the U1434 basalts are more enriched in incompatible elements than the U1433 samples. The SCS MORBs have mainly undergone the fractional crystallization of olivine, accompanied by the relatively weak fractional crystallization of plagioclase and clinopyroxene during magma evolution. The magma of both sites might be mainly produced by the high-degree partial melting of spinel peridotite at low pressures. The degree of partial melting at site U1434 was lower than at U1433, ascribed to the relatively lower spreading rate. The magmatic source of the southwest sub-basin basalts may be contaminated by lower continental crust and contributed by recycled oceanic crust component during the opening of the SCS.

Hydrous partial melting within the lower oceanic crust

Terra Nova ◽  
2005 ◽  
Vol 17 (3) ◽  
pp. 286-291 ◽  
Author(s):  
Juergen Koepke ◽  
Sandrin T. Feig ◽  
Jonathan Snow
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Lower Oceanic Crust

Geochemical characteristics of mafic lavas from the Neotethyan ophiolites in western Turkey: implications for heterogeneous source contribution during variable stages of ocean crust generation

2007 ◽  
Vol 145 (1) ◽  
pp. 37-54 ◽  
Author(s):  
E. ALDANMAZ ◽  
M. K. YALINIZ ◽  
A. GÜCTEKIN ◽  
M. C. GÖNCÜOĞLU
Keyword(s):  
Oceanic Crust ◽  
Mantle Source ◽  
Western Turkey ◽  
Source Contribution ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Mafic Lavas ◽  
Ocean Ridge ◽  
Heterogeneous Source ◽  
Subduction Component

AbstractThe Late Triassic to Late Cretaceous age mafic lavas from the Neotethyan suture zone ophiolites in western Turkey exhibit a wide diversity of geochemical signatures, indicating derivation from extremely heterogeneous mantle sources. The rocks as a whole can be divided into three broad subdivisions based on their bulk-rock geochemical characteristics: (1) mid-ocean ridge basalts (MORB) that range in composition from light rare earth element (LREE)-depleted varieties (N-MORB; (La/Sm)N<1) through transitional MORB to LREE enriched types (E-MORB; (La/Sm)N>1); (2) the ocean island basalt (OIB)-type alkaline volcanic rocks with significant enrichment in LILE, HFSE and L-MREE, and a slight depletion in HREE, relative to normal mid-ocean ridge basalts (N-MORB); and (3) the supra-subduction zone (SSZ)-type tholeiites originated from arc mantle sources that are characterized by selective enrichments in fluid-soluble large ion lithophile elements (LILE) and LREE relative to the high field strength elements (HFSE). The formation of MORB tholeiites with variable enrichments and depletions in incompatible trace elements is probably related to the processes of crust generation along an oceanic spreading system, and the observed MORB–OIB associations can be modelled by heterogeneous source contribution and mixing of melts from chemically discrete sources from sub-lithospheric reservoirs. Evaluation of trace element systematics shows that the inferred heterogeneities within the mantle source regions are likely to have originated from continuous processes of formation and destruction of enriched mantle domains by long-term plate recycling, convective mixing and melt extraction. The origin of SSZ-type tholeiites with back-arc basin affinities, on the other hand, can be attributed to the later intra-oceanic subduction and plate convergence which led to the generation of supra-subduction-type oceanic crust as a consequence of imparting a certain extent of subduction component into the mantle melting region. Mixing of melts from a multiply depleted mantle source, which subsequently received variable re-enrichment with a subduction component, is suggested to explain the generation of supra-subduction-type oceanic crust. The geodynamic setting in which much of the SSZ-type ophiolitic extrusive rocks from western Turkey were generated can be described as an arc-basin system that is characterized by an oceanic lithosphere generation most probably associated with melting of mantle material along a supra-subduction-type spreading centre.

Boninitic and tholeiitic dykes in the Lewis Hills mantle section of the Bay of Islands ophiolite: implications for magmatism adjacent to a fracture zone in a back-arc spreading environment

1995 ◽  
Vol 32 (12) ◽  
pp. 2128-2146 ◽  
Author(s):  
Stephen J. Edwards
Keyword(s):  
Partial Melting ◽  
Fracture Zone ◽  
Tholeiitic Magma ◽  
Suprasubduction Zone ◽  
Geochemical Study ◽  
Mid Ocean Ridge ◽  
Hill Area ◽  
Back Arc ◽  
Ocean Ridge ◽  
Mantle Section

A detailed, integrated field, petrographic, and geochemical study of the Springers Hill area of the Bay of Islands ophiolite exposed in the Lewis Hills was undertaken to explain the anomalously high abundance of veins and dykes of chromitite, orthopyroxenite, and clinopyroxenite, and their associated dunites, hosted by a refractory harzburgite–dunite mixture. A geodynamic situation is presented, which is constrained by previous studies requiring formation of the Springers Hill mantle section at a ridge–fracture zone intersection, and the whole of the Bay of Islands ophiolite within a back-arc spreading environment. The veins and dykes formed during magmatism at the ridge–fracture zone intersection and along the fracture zone, as progressively hotter, more fertile (richer in clinopyroxene) asthenosphere ascended and was channelled up and along the fracture zone wall. Shallow melting of refractory harzburgite in the presence of subduction-derived hydrous fluids produced light rare earth element (LREE)-enriched boninitic magma from which crystallized chromitites, some of their associated dunites, and orthopyroxenites. This melting event dehydrated much of the mantle in and around the zone of partial melting. Continued rise and shallow partial melting of hotter, more fertile mantle under conditions of variable hydration generated LREE-depleted, low-Ti tholeiitic magma. This magma crystallized olivine clinopyroxenite, some associated dunite, and clinopyroxenite. The final magmatic event may have involved partial melting of mid-ocean-ridge basalt-bearing mantle at depth, ascent of the magma, and formation of massive wehrlite–lherzolite bodies at the ridge–fracture zone intersection and along the fracture zone. Ridge–fracture zone intersections in suprasubduction-zone environments are sites of boninitic and tholeiitic magmatism because refractory asthenospheric mantle may melt as it is channelled with subduction-derived fluids to shallow depths by the old, cold lithospheric wall of the fracture zone. Heat for melting is provided by the ascent of hotter, more fertile mantle. Extremely refractory magmas do not occur along "normal" oceanic fracture zones because volumes of highly refractory mantle are much less, subduction-derived hydrous fluids are not present, and fracture zone walls extend to shallower depths.

Oxygen isotope geochemistry of rocks from DSDP Leg37

1977 ◽  
Vol 14 (4) ◽  
pp. 771-776 ◽  
Author(s):  
K. Muehlenbachs
Keyword(s):  
Isotopic Composition ◽  
Oxygen Isotope ◽  
Oceanic Crust ◽  
Isotope Geochemistry ◽  
Altered Rock ◽  
Ocean Ridges ◽  
Dredged Materials ◽  
Mid Ocean Ridge ◽  
Intrusive Rocks ◽  
Ocean Ridge

The isotopic compositions of minerals separated from DSDP Leg 37 samples indicate that the primary, unaltered δ18O of both the intrusive and extrusive rocks are identical (~5.7 ‰, SMOW) to those of unaltered basalts dredged from mid-ocean ridges. All of the analyzed basalts (6 to 10 ‰) have been enriched in 18O due to weathering by cold seawater, whereas the intrusive rocks (2.4 and 5.0 ‰) are depleted of 18O probably as a result of exchange with hot seawater at the mid-ocean ridge. Both kinds of altered rock are also known from the study of dredged materials. 18O is preferentially removed from seawater by the first process, but is added to seawater by the second. Exchange of oxygen between oceanic crust and seawater must be considered in any discussion of the evolution of the isotopic composition of the oceans, because large volumes of rock are altered each year as the oceanic crust is formed.

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