1
|
Turner SJ, Langmuir CH. An alternative to the igneous crust fluid + sediment melt paradigm for arc lava geochemistry. SCIENCE ADVANCES 2024; 10:eadg6482. [PMID: 38875329 PMCID: PMC11177931 DOI: 10.1126/sciadv.adg6482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Accepted: 05/13/2024] [Indexed: 06/16/2024]
Abstract
A long-standing paradigm of arc geochemistry is that the trace element compositions of arc lavas arise from two compositionally distinct slab components: an aqueous dehydration fluid from the subducting igneous ocean crust that transports "fluid-mobile" elements, such as barium (Ba), and a sediment melt that supplies thorium (Th) and the light rare earth elements. This two-component framework has been widely called upon to explain global geochemical trends as well as geochemical variations within individual arcs, such as the Marianas. Here, we show that this paradigm is inconsistent with mass balance, due to the low Ba contents of igneous ocean crust, and with experimental data, which show that aqueous fluids from the igneous oceanic crust would be too dilute to substantially affect arc compositions. Observations previously attributed to the sediment melt/igneous-crust-fluid hypothesis are better explained by diverse subducting sediment compositions coupled with ambient mantle wedge heterogeneity, both globally and for the Marianas.
Collapse
Affiliation(s)
- Stephen J Turner
- University of Houston, Houston, TX, USA
- University of Massachusetts Amherst, Amherst, MA, USA
| | | |
Collapse
|
2
|
Qin Z, Tao H, Xie Z, Liu Y. Petrogenesis and geodynamic implications of the Late Devonian dioritic and granitic intrusive rocks in the Dananhu Belt, Eastern Tianshan Orogenic Belt. Heliyon 2024; 10:e26053. [PMID: 38390074 PMCID: PMC10881888 DOI: 10.1016/j.heliyon.2024.e26053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 02/06/2024] [Accepted: 02/07/2024] [Indexed: 02/24/2024] Open
Abstract
The Late Devonian magmatism of the Dananhu arc belt in the Central Asian Orogenic Belt provides a critical geological record. This study provides new comprehensive geochronological, geochemical, and Sr-Nd isotopic data of granodioritic and dioritic intrusions in the Dananhu belt. These findings contribute to unraveling the regional tectonic history and constraining the geodynamic processes involved. Zircon U-Pb dating indicates that the granodiorites and diorites were formed at 382.7 ± 3.8Ma and 363.1 ± 4.3Ma, respectively. The granodiorites show characteristics similar to I-type granites with high SiO2, low MgO and Mg# and aluminium saturation index (<1.1), negligible Eu anomalies, low (K2O + Na2O)/CaO ratios and zircon saturation temperatures (average = 696 °C). Granodiorites also show depleted isotope signatures (εNd(t) = +5.85 to +6.27 and low (87Sr/86Sr)i = 0.704082-0.704583) and juvenile TDM ages (741-793Ma), indicating their origin from a juvenile crust. The diorites are characterized by enrichments in large ion lithophile elements, U and Pb, but depleted in Nb and Ta displaying typical geochemical features of a subduction-related origin, together with high εNd(t) (+6.10 to +6.84) and low initial Sr isotopes (0.703745-0.704601), suggesting that they originated from a subduction fluid modified depleted mantle. The petrogenesis of both granodiorites and diorites in the Dananhu arc provides evidence that they formed through magmatic processes in a subduction tectonic setting. Considering the adakites associated with slab melting from previous studies in the Dananhu arc, it is plausible that the north-dipping subduction of the North Tianshan oceanic lithosphere have contributed to the Dananhu arc magmatism during the Late Devonian.
Collapse
Affiliation(s)
- Zhen Qin
- Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Huifei Tao
- Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China
- National Engineering Research Center of Offshore Oil and Gas Exploration, 100027, China
| | - Zaibo Xie
- Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yutong Liu
- Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| |
Collapse
|
3
|
Late Ordovician Mafic Magmatic Event, Southeast Siberia: Tectonic Implications, LIP Interpretation, and Potential Link with a Mass Extinction. MINERALS 2020. [DOI: 10.3390/min10121108] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
A geochronological, isotopic, and geochemical study of the Suordakh event of mafic magmatic intrusions on the southeast Siberian margin was undertaken. U-Pb baddeleyite dating of a mafic sill intruding lower Cambrian rocks, yielded a 458 ± 13 Ma emplacement age. The chemical composition and stratigraphic setting of this dated sill differed from that previously attributed to the Suordakh event, implying that additional intrusions, previously mapped as Devonian, potentially belonged to the Suordakh event. No correlation between L.O.I. and concentration of highly mobile major and trace elements was documented, showing small or no influence of hydrothermal alteration on the chemical composition of the intrusions. A new tectonic reconstruction located an island arc and active margin relatively close to the study area. However, all samples had chemical compositions close to that of OIB and did not display Ta-Nb and Ti-negative anomalies, nor other features typical for subduction-related magmatism. The major and trace element distribution was most characteristic of within-plate basalts with the mantle source composition being transitional from spinel to garnet lherzolite. Combining four U-Pb baddeleyite dates of mafic sills and dykes from southeast Siberia, the age of the Suordakh event was estimated at 454 ± 10 Ma. The area of the Suordakh event was at least 35,000–40,000 km2 (an estimate including sills previously interpreted as Devonian), and could be increased with additional dating in Southeastern Siberia. Similar ages for within-plate intrusions were reported from South Korea, West Mongolia, South Argentina, North Iran and Northwest Canada, and these ca. 450 Ma ages were collectively close in timing with the latest Ordovician (Hirnantian) mass extinction. More high-precision dating is necessary to fully test a link between the Suordakh event (and the other age-correlative events) and the end-Ordovician mass extinction.
Collapse
|
4
|
Geochronology, Geochemistry, and Geodynamic Relationship of the Mafic Dykes and Granites in the Qianlishan Complex, South China. MINERALS 2020. [DOI: 10.3390/min10121069] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The Qianlishan complex, located in Hunan Province of South China, is closely associated with intense W-dominated polymetallic mineralization. The Qianlishan complex is composed of three phases: the main-phase porphyritic and equigranular granites, granite porphyry, and mafic dykes. Geochronologically, the zircon U-Pb dating results show that the porphyritic and equigranular granites have ages of approximately 159 and 158 Ma, respectively, similar to those of mafic dykes (approximately 158 Ma), while the granite porphyry was formed later at approximately 145 Ma. Geochemically, the mafic dykes are characterized by calc-alkaline high-Mg andesite (HMA) with high MgO, TiO2, Mg#, and CA/TH index. They exhibit significantly depleted εNd(t) and εHf(t) with high Ba/La, La/Nb, and (La/Yb)N, indicating that they formed from mixing melts of depleted asthenospheric mantle and metasomatized subcontinental lithospheric mantle (SCLM). The main-phase granites are peraluminous and are characterized by high SiO2, low (La/Yb)N ratios, and relative depletion in Ba, Sr, Ti, and Eu. They also display negative correlations between La, Ce, Y, and Rb contents, suggesting that they are highly fractionated S-type granites. Furthermore, they show high εNd(t) and εHf(t), CaO/Na2O ratios, HREE, and Y contents, indicating that they were produced by parental melting of ancient basement mixed with mantle-derived components. In contrast, the granite porphyry shows A-type signature granites, with higher εNd(t) and εHf(t) and CaO/Na2O ratios than the main-phase granites but similar Zr/Nb and Zr/Hf ratios to the mafic dykes, suggesting that they are the products of partial melting of a hybrid source with ancient basement and the mafic dykes. We thus infer that the slab roll-back led to generation of Qianlishan back-arc basalt and HMA and further triggered the formation of the Qianlishan granite.
Collapse
|
5
|
Richter M, Nebel O, Maas R, Mather B, Nebel-Jacobsen Y, Capitanio FA, Dick HJB, Cawood PA. An Early Cretaceous subduction-modified mantle underneath the ultraslow spreading Gakkel Ridge, Arctic Ocean. SCIENCE ADVANCES 2020; 6:6/44/eabb4340. [PMID: 33127673 PMCID: PMC7608816 DOI: 10.1126/sciadv.abb4340] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Accepted: 09/14/2020] [Indexed: 06/11/2023]
Abstract
Earth's upper mantle, as sampled by mid-ocean ridge basalts (MORBs) at oceanic spreading centers, has developed chemical and isotopic heterogeneity over billions of years through focused melt extraction and re-enrichment by recycled crustal components. Chemical and isotopic heterogeneity of MORB is dwarfed by the large compositional spectrum of lavas at convergent margins, identifying subduction zones as the major site for crustal recycling into and modification of the mantle. The fate of subduction-modified mantle and if this heterogeneity transmits into MORB chemistry remains elusive. Here, we investigate the origin of upper mantle chemical heterogeneity underneath the Western Gakkel Ridge region in the Arctic Ocean through MORB geochemistry and tectonic plate reconstruction. We find that seafloor lavas from the Western Gakkel Ridge region mirror geochemical signatures of an Early Cretaceous, paleo-subduction zone, and conclude that the upper mantle can preserve a long-lived, stationary geochemical memory of past geodynamic processes.
Collapse
Affiliation(s)
- Marianne Richter
- Isotopia Laboratory, School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia.
- School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
| | - Oliver Nebel
- Isotopia Laboratory, School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
- School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
| | - Roland Maas
- School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Ben Mather
- School of Geosciences, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Yona Nebel-Jacobsen
- Isotopia Laboratory, School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
- School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
| | - Fabio A Capitanio
- School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
| | - Henry J B Dick
- Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543-1539, USA
| | - Peter A Cawood
- Isotopia Laboratory, School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
- School of Earth, Atmosphere and Environment, Monash University, Clayton, Victoria 3800, Australia
| |
Collapse
|
6
|
Wang Q, Hawkesworth CJ, Wyman D, Chung SL, Wu FY, Li XH, Li ZX, Gou GN, Zhang XZ, Tang GJ, Dan W, Ma L, Dong YH. Pliocene-Quaternary crustal melting in central and northern Tibet and insights into crustal flow. Nat Commun 2016; 7:11888. [PMID: 27307135 PMCID: PMC4912662 DOI: 10.1038/ncomms11888] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Accepted: 05/10/2016] [Indexed: 11/10/2022] Open
Abstract
There is considerable controversy over the nature of geophysically recognized low-velocity–high-conductivity zones (LV–HCZs) within the Tibetan crust, and their role in models for the development of the Tibetan Plateau. Here we report petrological and geochemical data on magmas erupted 4.7–0.3 Myr ago in central and northern Tibet, demonstrating that they were generated by partial melting of crustal rocks at temperatures of 700–1,050 °C and pressures of 0.5–1.5 GPa. Thus Pliocene-Quaternary melting of crustal rocks occurred at depths of 15–50 km in areas where the LV–HCZs have been recognized. This provides new petrological evidence that the LV–HCZs are sources of partial melt. It is inferred that crustal melting played a key role in triggering crustal weakening and outward crustal flow in the expansion of the Tibetan Plateau. The role of the low velocity-high conductivity zones (LV–HCZs) in developing the Tibetan Plateau has remained controversial. Here, Wang et al. present new geochemical and petrological data that show the LV–HCZs are sources of partial melt thus giving insight into the development of the Tibetan Plateau.
Collapse
Affiliation(s)
- Qiang Wang
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.,CAS Center for Excellence in Tibetan Plateau Earth Sciences (CETES), Beijing 100101, China
| | - Chris J Hawkesworth
- School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK.,Department of Earth and Environmental Sciences, University of St Andrews, North Street, St Andrews KY16 9AL, UK
| | - Derek Wyman
- School of Geosciences, The University of Sydney, Sydney, New South Wales 2006, Australia
| | - Sun-Lin Chung
- Institute of Earth Sciences, Academia Sinica, Nangang, Taipei 11529, Taiwan.,Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan
| | - Fu-Yuan Wu
- Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
| | - Xian-Hua Li
- Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
| | - Zheng-Xiang Li
- ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, Perth, Western Australia 6845, Australia
| | - Guo-Ning Gou
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Xiu-Zheng Zhang
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Gong-Jian Tang
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Wei Dan
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Lin Ma
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| | - Yan-Hui Dong
- State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
| |
Collapse
|
7
|
Hou Z, Liu Y, Tian S, Yang Z, Xie Y. Formation of carbonatite-related giant rare-earth-element deposits by the recycling of marine sediments. Sci Rep 2015; 5:10231. [PMID: 26035414 PMCID: PMC4451788 DOI: 10.1038/srep10231] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2014] [Accepted: 04/02/2015] [Indexed: 11/13/2022] Open
Abstract
Carbonatite-associated rare-earth-element (REE) deposits are the most significant source of the world’s REEs; however, their genesis remains unclear. Here, we present new Sr-Nd-Pb and C-O isotopic data for Cenozoic carbonatite-hosted giant REE deposits in southwest China. These REE deposits are located along the western margin of the Yangtze Craton that experienced Proterozoic lithospheric accretion, and controlled by Cenozoic strike-slip faults related to Indo-Asian continental collision. The Cenozoic carbonatites were emplaced as stocks or dykes with associated syenites, and tend to be extremely enriched in Ba, Sr, and REEs and have high 87Sr/86Sr ratios (>0.7055). These carbonatites were likely formed by melting of the sub-continental lithospheric mantle (SCLM), which had been previously metasomatized by high-flux REE- and CO2-rich fluids derived from subducted marine sediments. The fertility of these carbonatites depends on the release of REEs from recycled marine sediments and on the intensity of metasomatic REE refertilization of the SCLM. We suggest that cratonic edges, particularly along ancient convergent margins, possess the optimal configuration for generating giant REE deposits; therefore, areas of metamorphic basement bounded or cut by translithospheric faults along cratonic edges have a high potential for such deposits.
Collapse
Affiliation(s)
- Zengqian Hou
- 1] State Key Laboratory of Continental Tectonics and Dynamics Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, P. R. China [2] Continental Tectonics Centre, Northwestern University, Xi'an, P.R. China
| | - Yan Liu
- State Key Laboratory of Continental Tectonics and Dynamics Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, P. R. China
| | - Shihong Tian
- Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, P.R. China
| | - Zhiming Yang
- State Key Laboratory of Continental Tectonics and Dynamics Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, P. R. China
| | - Yuling Xie
- University of Science and Technology, Beijing, Beijing 100083, P. R. China
| |
Collapse
|
8
|
Davis RE, Moyer CL. Extreme spatial and temporal variability of hydrothermal microbial mat communities along the Mariana Island Arc and southern Mariana back-arc system. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007jb005413] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Richard E. Davis
- Biology Department; Western Washington University; Bellingham Washington USA
| | - Craig L. Moyer
- Biology Department; Western Washington University; Bellingham Washington USA
| |
Collapse
|
9
|
Fan W, Guo F, Wang Y, Zhang H. Late Mesozoic mafic magmatism from the North China Block: constraints on chemical and isotopic heterogeneity of the subcontinental lithospheric mantle. ACTA ACUST UNITED AC 2007. [DOI: 10.1144/sp280.4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractAvailable major, trace element and Sr–Nd isotope data for the late Mesozoic mafic rocks in the eastern North China Block (NCB) show chemical and isotopic differences between rocks from different tectonic units. Such differences are interpreted as signatures inherited from the melted mantle sources, which had experienced distinctive enrichment processes during lithospheric evolution. The subcontinental lithospheric mantle beneath the NCB interior is characterized by long-term light REE (LREE) enrichment and EM1-like Sr–Nd isotopic signatures. Such a lithospheric mantle is mainly composed of chemically refractory peridotites that are common in cratonic regions. In contrast to that of the NCB interior, beneath the northern part of the NCB a relatively chemically fertile mantle was enriched in large ion lithophile elements and LREE and depleted in Nb–Ta and Th–U. It has higher 87Sr/86Sr(i) and εNd(t) than that of the interior of the block, and is interpreted to have been modified by recycled lower continental crust components related to the palaeo-Asian Ocean subduction. The lithospheric mantle beneath the southern NCB has the highest 87Sr/86Sr(i) and the lowest εNd(t), and is chemically transitional between the interior and northern part of the block. Formation of such an enriched lithospheric mantle was closely associated with modification from the subducted Yangtze lower–middle crust during Triassic collision between the North China and Yangtze Blocks. A lithospheric extension–thinning model is proposed to explain the petrogenesis of these late Mesozoic mafic rocks in the eastern North China Block. This process was amplified by effects from surrounding plate interactions, including the rapid northward movement of the palaeo-Pacific Ocean, compressional forces from the Siberian plate, the Tethyan tectonic belt and possibly the Indo-China Block. The resultant forces triggered lithospheric extension, asthenospheric upwelling, and decompressional melting of the enriched mantle sources.
Collapse
Affiliation(s)
- W. Fan
- Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou, 510640, China (e-mail:)
| | - F. Guo
- Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou, 510640, China (e-mail:)
| | - Y. Wang
- Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou, 510640, China (e-mail:)
| | - H. Zhang
- Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
| |
Collapse
|
10
|
Abstract
The continental crust covers nearly a third of the Earth's surface. It is buoyant--being less dense than the crust under the surrounding oceans--and is compositionally evolved, dominating the Earth's budget for those elements that preferentially partition into silicate liquid during mantle melting. Models for the differentiation of the continental crust can provide insights into how and when it was formed, and can be used to show that the composition of the basaltic protolith to the continental crust is similar to that of the average lower crust. From the late Archaean to late Proterozoic eras (some 3-1 billion years ago), much of the continental crust appears to have been generated in pulses of relatively rapid growth. Reconciling the sedimentary and igneous records for crustal evolution indicates that it may take up to one billion years for new crust to dominate the sedimentary record. Combining models for the differentiation of the crust and the residence time of elements in the upper crust indicates that the average rate of crust formation is some 2-3 times higher than most previous estimates.
Collapse
Affiliation(s)
- C J Hawkesworth
- Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK.
| | | |
Collapse
|
11
|
The zircon SHRIMP chronology and trace element geochemistry of the Carboniferous volcanic rocks in western Tianshan Mountains. ACTA ACUST UNITED AC 2005. [DOI: 10.1007/bf03182672] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
|
12
|
Kessel R, Schmidt MW, Ulmer P, Pettke T. Trace element signature of subduction-zone fluids, melts and supercritical liquids at 120–180 km depth. Nature 2005; 437:724-7. [PMID: 16193050 DOI: 10.1038/nature03971] [Citation(s) in RCA: 905] [Impact Index Per Article: 47.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2005] [Accepted: 06/24/2005] [Indexed: 11/08/2022]
Abstract
Fluids and melts liberated from subducting oceanic crust recycle lithophile elements back into the mantle wedge, facilitate melting and ultimately lead to prolific subduction-zone arc volcanism. The nature and composition of the mobile phases generated in the subducting slab at high pressures have, however, remained largely unknown. Here we report direct LA-ICPMS measurements of the composition of fluids and melts equilibrated with a basaltic eclogite at pressures equivalent to depths in the Earth of 120-180 km and temperatures of 700-1,200 degrees C. The resultant liquid/mineral partition coefficients constrain the recycling rates of key elements. The dichotomy of dehydration versus melting at 120 km depth is expressed through contrasting behaviour of many trace elements (U/Th, Sr, Ba, Be and the light rare-earth elements). At pressures equivalent to 180 km depth, however, a supercritical liquid with melt-like solubilities for the investigated trace elements is observed, even at low temperatures. This mobilizes most of the key trace elements (except the heavy rare-earth elements, Y and Sc) and thus limits fluid-phase transfer of geochemical signatures in subduction zones to pressures less than 6 GPa.
Collapse
Affiliation(s)
- Ronit Kessel
- Institute of Earth Science, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel.
| | | | | | | |
Collapse
|
13
|
George R, Turner S, Hawkesworth C, Morris J, Nye C, Ryan J, Zheng SH. Melting processes and fluid and sediment transport rates along the Alaska-Aleutian arc from an integrated U-Th-Ra-Be isotope study. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2002jb001916] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Rhiannon George
- Department of Earth Sciences; University of Bristol; Bristol UK
| | - Simon Turner
- Department of Earth Sciences; University of Bristol; Bristol UK
| | | | - Julie Morris
- Department of Earth and Planetary Sciences; Washington University; Saint Louis Missouri USA
| | - Chris Nye
- Alaska Volcano Observatory; Alaska Division of Geological and Geophysical Surveys; Fairbanks Alaska USA
| | - Jeff Ryan
- Department of Geology; University of South Florida-Tampa; Tampa Florida USA
| | - Shu-Hui Zheng
- Department of Earth System Science; University of California; Irvine California USA
| |
Collapse
|
14
|
Kincaid C, Hall PS. Role of back arc spreading in circulation and melting at subduction zones. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2001jb001174] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Chris Kincaid
- Graduate School of Oceanography; University of Rhode Island; Narragansett Rhode Island USA
| | - Paul S. Hall
- Graduate School of Oceanography; University of Rhode Island; Narragansett Rhode Island USA
| |
Collapse
|
15
|
Tamura Y. Some geochemical constraints on hot fingers in the mantle wedge: evidence from NE Japan. ACTA ACUST UNITED AC 2003. [DOI: 10.1144/gsl.sp.2003.219.01.11] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractMantle melting and the production of magmas along the NE Japan arc may be controlled by hot regions in the mantle wedge (hot fingers) that move toward the volcanic front along upward-sloping trajectories. At depths equivalent to 1–2 GPa, where magmas are expected to segregate from mantle diapirs, the hot-finger structures result in a decreasing thermal gradient away from volcanic front. Low-alkali tholeiite is therefore formed by the greater degree of diapiric melting near the volcanic front; high-alumina basalt and alkali olivine basalt are produced by lesser degrees of diapiric melting to the west. The grouping of volcanoes at the volcanic front is interpreted as being controlled by thermal structure in the mantle wedge, and groups are concentrated above the tips of the hot fingers. Map-view variations of minimum 87Sr/86Sr of NE Japan volcanoes are interpreted as resulting from transport of fertile and high-87Sr/86Sr mantle material into the magma source region in the hot fingers. Given that mantle diapirs are formed in the lower part of the mantle wedge, a greater proportion of fertile material will be contained in the diapirs at the tips of the hot fingers, resulting in higher 87Sr/86Sr magmas along the volcanic front. Conveyor-like return flow carries the sheet-like remnants of the fingers to depth along the top of the subducting slab.
Collapse
Affiliation(s)
- Y. Tamura
- Institute for Frontier Research on Earth Evolution (IFREE), Japan Marine Science and Technology Centre (JAMSTEC)
Yokosuka 237-0061, Japan
| |
Collapse
|
16
|
Kelemen PB, Rilling JL, Parmentier EM, Mehl L, Hacker BR. Thermal structure due to solid-state flow in the mantle wedge beneath arcs. INSIDE THE SUBDUCTION FACTORY 2003. [DOI: 10.1029/138gm13] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
|
17
|
Kelemen PB, Yogodzinski GM, Scholl DW. Along-strike variation in the Aleutian Island Arc: Genesis of high Mg# andesite and implications for continental crust. INSIDE THE SUBDUCTION FACTORY 2003. [DOI: 10.1029/138gm11] [Citation(s) in RCA: 176] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
|
18
|
Seismological constraints on structure and flow patterns within the mantle wedge. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/138gm05] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
|
19
|
Abstract
AbstractThe South Sandwich Islands are one of the world’s classic examples of an intraoceanic arc. Formed on recently generated back-arc crust, they represent the earliest stages of formation of arc crust, and are an excellent laboratory for investigating variations in magma chemistry resulting from mantle processes, and generation of silicic magmas in a dominantly basaltic environment. Two volcanoes are examined. Southern Thule in the south of the arc is a complex volcanic edifice with three calderas and compositions that range from mafic to silicic and tholeiitic to calc-alkaline. It is compared to the Candlemas-Vindication edifice in the north of the arc, which is low-K tholeiitic and strongly bimodal from mafic to silicic. Critically, Southern Thule lies along a cross-arc, wide-angle seismic section that reveals the velocity structure of the underlying arc crust. Trace element variations are used to argue that the variations in both mantle depletion and input of a subducted sediment component produced the diverse low-K tholeiite, tholeiite and calc-alkaline series. Primitive, mantle-derived melts fractionally crystallized by c. 36% to produce the most Mg-rich erupted basalts and a high-velocity cumulitic crustal keel. Plagioclase cumulation produced abundant high-Al basalts (especially in the tholeiitic series), and strongly influenced Sr abundances in the magmas. However, examination of volumetric and geochemical arguments indicates that the silicic rocks do not result from fractional crystallization, and are melts of amphibolitic arc crust instead.
Collapse
Affiliation(s)
- P. T. Leat
- British Antarctic Survey
High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - J. L. Smellie
- British Antarctic Survey
High Cross, Madingley Road, Cambridge CB3 0ET, UK
| | - I. L. Millar
- British Antarctic Survey, c/o NERC Isotope Geoscience Laboratory, Kingsley Dunham Centre
Keyworth, Nottingham NG12 5GG, UK
| | - R. D. Larter
- British Antarctic Survey
High Cross, Madingley Road, Cambridge CB3 0ET, UK
| |
Collapse
|
20
|
Turner SP. On the time-scales of magmatism at island-arc volcanoes. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2002; 360:2853-2871. [PMID: 12626270 DOI: 10.1098/rsta.2002.1060] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Precise information on time-scales and rates of change is fundamental to an understanding of natural processes and the development of quantitative physical models in the Earth sciences. U-series isotope studies are revolutionizing this field by providing time information in the range 10(2)-10(4) years, which is similar to that of many modern Earth processes. I review how the application of U-series isotopes has been used to constrain the time-scales of magma formation, ascent and storage beneath island-arc volcanoes. Different elements are distilled-off the subducting plate at different times and in different places. Contributions from subducted sediments to island-arc lava sources appear to occur some 350 kyr to 4 Myr prior to eruption. Fluid release from the subducting oceanic crust into the mantle wedge may be a multi-stage process and occurs over a period ranging from a few hundred kyr to less than one kyr prior to eruption. This implies that dehydration commences prior to the initiation of partial melting within the mantle wedge, which is consistent with recent evidence that the onset of melting is controlled by an isotherm and thus the thermal structure within the wedge. U-Pa disequilibria appear to require a component of decompression melting, possibly due to the development of gravitational instabilities. The preservation of large (226)Ra disequilibria permits only a short period of time between fluid addition and eruption. This requires rapid melt segregation, magma ascent by channelled flow and minimal residence time within the lithosphere. The evolution from basalt to basaltic andesite probably occurs rapidly during ascent or in magma reservoirs inferred from some geophysical data to lie within the lithospheric mantle. The flux across the Moho is broadly andesitic, and some magmas subsequently stall in more shallow crustal-level magma chambers, where they evolve to more differentiated compositions on time-scales of a few thousand years or less.
Collapse
Affiliation(s)
- S P Turner
- Department of Earth Sciences, Wills Memorial Building, University of Bristol, Bristol BS8 1RJ, UK
| |
Collapse
|
21
|
Macpherson CG, Hall R. Timing and tectonic controls in the evolving orogen of SE Asia and the western Pacific and some implications for ore generation. ACTA ACUST UNITED AC 2002. [DOI: 10.1144/gsl.sp.2002.204.01.04] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractSE Asia lies at the convergence of the Eurasian, Pacific and Australian plates. The region is made up of many active arcs, extensional basins, and the remnants of similar tectonic environments developed throughout the Cenozoic. There are many important hydrothermal mineral deposits and prospects in SE Asia but their formation is often poorly understood due to the complicated tectonic history of this region and the knowledge of relationships between mineralization and tectonics. Plate reconstruction offers a framework to integrate geological and geochemical data that can be used to unravel the large-scale tectonic processes that affected mineralized provinces. We present examples of the information that can be derived from this approach and discuss the implications for understanding the origin of some hydrothermal mineral deposits in SE Asia.
Collapse
Affiliation(s)
- Colin G. Macpherson
- Department of Geological Sciences, University of Durham
South Road, Durham DH1 3LE, UK
| | - Robert Hall
- SE Asia Research Group, Department of Geology, Royal Holloway University of London
Egham, Surrey TW20 0EX, UK
| |
Collapse
|
22
|
Abstract
Recent geochemical studies of uranium-thorium series disequilibrium in rocks from subduction zones require magmas to be transported through the mantle from just above the subducting slab to the surface in as little as approximately 30,000 years. We present a series of laboratory experiments that investigate the characteristic time scales and flow patterns of the diapiric upwelling model of subduction zone magmatism. Results indicate that the interaction between buoyantly upwelling diapirs and subduction-induced flow in the mantle creates a network of low-density, low-viscosity conduits through which buoyant flow is rapid, yielding transport times commensurate with those indicated by uranium-thorium studies.
Collapse
Affiliation(s)
- P S Hall
- Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA.
| | | |
Collapse
|
23
|
Turner S, Evans P, Hawkesworth C. Ultrafast Source-to-Surface Movement of Melt at Island Arcs from
226
Ra-
230
Th Systematics. Science 2001; 292:1363-6. [PMID: 11359009 DOI: 10.1126/science.1059904] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Island arc lavas have radium-226 excesses that extend to higher values than those observed in mid-ocean ridge or ocean island basalts. The initial ratio of radium-226 to thorium-230 is largest in the most primitive lavas, which also have the highest barium/thorium ratios, and decreases with increasing magmatic differentiation. Therefore, the radium-226 excesses appear to have been introduced into the base of the mantle melting column by fluids released from the subducting plate. Preservation of this signal requires transport to the surface arguably in only a few hundreds of years and directly constrains the average melt velocity to the order of 1000 meters per year. Thus, melt segregation and channel formation can occur rapidly in the mantle.
Collapse
Affiliation(s)
- S Turner
- Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK.
| | | | | |
Collapse
|
24
|
Prouteau G, Scaillet B, Pichavant M, Maury R. Evidence for mantle metasomatism by hydrous silicic melts derived from subducted oceanic crust. Nature 2001; 410:197-200. [PMID: 11242077 DOI: 10.1038/35065583] [Citation(s) in RCA: 385] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The low concentrations of niobium, tantalum and titanium observed in island-arc basalts are thought to result from modification of the sub-arc mantle by a metasomatic agent, deficient in these elements, that originates from within the subducted oceanic crust. Whether this agent is an hydrous fluid or a silica-rich melt has been discussed using mainly a trace-element approach and related to variable thermal regimes of subduction zones. Melting of basalt in the absence of fluid both requires high temperatures and yields melt compositions unlike those found in most modern or Mesozoic island arcs. Thus, metasomatism by fluids has been thought to be the most common situation. Here, however, we show that the melting of basalt under both H2O-added and low-temperature conditions can yield extremely alkali-rich silicic liquids, the alkali content of which increases with pressure. These liquids are deficient in titanium and in the elements niobium and tantalum and are virtually identical to glasses preserved in mantle xenoliths found in subduction zones and to veins found in exhumed metamorphic terranes of fossil convergent zones. We also found that the interaction between such liquids and mantle olivine produces modal mineralogies that are identical to those observed in metasomatized Alpine-type peridotites. We therefore suggest that mantle metasomatism by slab-derived melt is a more common process than previously thought.
Collapse
Affiliation(s)
- G Prouteau
- UMR 6538, UBO, 6 avenue Le Gargeu, P.B. 809, 29285 Brest, France
| | | | | | | |
Collapse
|
25
|
Turner S, Hawkesworth C. Constraints on flux rates and mantle dynamics beneath island arcs from Tonga–Kermadec lava geochemistry. Nature 1997. [DOI: 10.1038/39257] [Citation(s) in RCA: 143] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|