Highly siderophile element geochemistry and Re–Os isotopic systematics of carbonatites: Insights from Tamil Nadu, India

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00025798%3A_____%2F19%3A00000017" target="_blank" >RIV/00025798:_____/19:00000017 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/67985831:_____/19:00505893 RIV/00216208:11310/19:10402370

Výsledek na webu

<a href="https://www.sciencedirect.com/science/article/pii/S0012821X19303115" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0012821X19303115</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.epsl.2019.05.035" target="_blank" >10.1016/j.epsl.2019.05.035</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Highly siderophile element geochemistry and Re–Os isotopic systematics of carbonatites: Insights from Tamil Nadu, India

Popis výsledku v původním jazyce

Carbonatite metasomatism has been widely implicated for worldwide mafic mantle suites but so far, no combined data have been available for highly siderophile element systematics (HSE – Os, Ir, Ru, Pt, Pd, Re) and Re–Os isotopic compositions in carbonatites themselves. We present the first systematic survey of the HSE and Re–Os isotopic compositions in a suite of well-characterized Neoproterozoic carbonatites, silicocarbonatites and associated silicate rocks (pyroxenites, monzogabbros, syenites) from south India in order to place constraints on the HSE systematics in carbonatite magmas, anchoring possible mantle sources of carbonatites and relationship to the ambient crustal lithologies as well as preliminary constraints on carbonatite metasomatism in Earth’s mantle. The most plausible explanation for generally low HSE contents in calciocarbonatites from Tamil Nadu (sum HSE <1.22 ppb) involves a low-degree (<1 per cent) partial melting of the mantle source producing sulfur-saturated carbonatitic magmas leaving behind sulfide phases retaining HSE. The new data also indicate a strong FeO control on the distribution of Os and Pt during segregation of carbonatite melt from its enriched mantle source and/or melt differentiation. The combined 187Re/188Os values (from 0.10 to 217), 187Os/188Os ratios (0.186–10.4) and initial gamma Os values back-calculated to 800 Ma (from +0.1 to +6052) predict that most Tamil Nadu calciocarbonatites were plausibly derived from a carbonated peridotite source with <10 per cent recycled component. This model would thus provide significant constraints on the origin/source of carbonatites, irrespective of their post-emplacement history. The unusual, volumetrically rare, Mg–Cr-rich silicocarbonatites (sum HSE = 14–41 ppb) display almost identical HSE patterns with those of host pyroxenites and predominantly high Pt (up to 38 ppb), the origin of which remains unknown. Positive co-variations between Pt, Pd and Re, and the well-developed positive correlation between Pt and MgO in these Mg–Cr-rich silicocarbonatites argue for a source coming predominantly from the upper mantle. The Re–Os isotopic systematics agree with direct incorporation of enriched mantle-derived material into parental melts but variable incorporation of potassium-rich crustal materials is evidenced by highly positive gamma Os 800 Ma values for a sub-suite of Mg–Cr-rich silicocarbonatites, indicating intense fenitization. The highly radiogenic Os isotopic compositions of monzogabbros and a syenite argue for their derivation from crustal lithologies with no or only negligible contribution of mantle material. Collectively, low Ir, Ru, Pt and Pd contents found in the Tamil Nadu carbonatites appear to indicate the incapability to significantly modify the total budget of these elements in the Earth’s mantle during carbonatite metasomatism. In contrast, very high Re/Os ratios found in some of the analyzed carbonatites, paralleled by extremely radiogenic 187Os/188Os signature, can produce large modification of the Re–Os isotopic composition of mantle peridotites during carbonatite melt percolation when high melt/rock ratios are achieved.

Název v anglickém jazyce

Highly siderophile element geochemistry and Re–Os isotopic systematics of carbonatites: Insights from Tamil Nadu, India

Popis výsledku anglicky

Carbonatite metasomatism has been widely implicated for worldwide mafic mantle suites but so far, no combined data have been available for highly siderophile element systematics (HSE – Os, Ir, Ru, Pt, Pd, Re) and Re–Os isotopic compositions in carbonatites themselves. We present the first systematic survey of the HSE and Re–Os isotopic compositions in a suite of well-characterized Neoproterozoic carbonatites, silicocarbonatites and associated silicate rocks (pyroxenites, monzogabbros, syenites) from south India in order to place constraints on the HSE systematics in carbonatite magmas, anchoring possible mantle sources of carbonatites and relationship to the ambient crustal lithologies as well as preliminary constraints on carbonatite metasomatism in Earth’s mantle. The most plausible explanation for generally low HSE contents in calciocarbonatites from Tamil Nadu (sum HSE <1.22 ppb) involves a low-degree (<1 per cent) partial melting of the mantle source producing sulfur-saturated carbonatitic magmas leaving behind sulfide phases retaining HSE. The new data also indicate a strong FeO control on the distribution of Os and Pt during segregation of carbonatite melt from its enriched mantle source and/or melt differentiation. The combined 187Re/188Os values (from 0.10 to 217), 187Os/188Os ratios (0.186–10.4) and initial gamma Os values back-calculated to 800 Ma (from +0.1 to +6052) predict that most Tamil Nadu calciocarbonatites were plausibly derived from a carbonated peridotite source with <10 per cent recycled component. This model would thus provide significant constraints on the origin/source of carbonatites, irrespective of their post-emplacement history. The unusual, volumetrically rare, Mg–Cr-rich silicocarbonatites (sum HSE = 14–41 ppb) display almost identical HSE patterns with those of host pyroxenites and predominantly high Pt (up to 38 ppb), the origin of which remains unknown. Positive co-variations between Pt, Pd and Re, and the well-developed positive correlation between Pt and MgO in these Mg–Cr-rich silicocarbonatites argue for a source coming predominantly from the upper mantle. The Re–Os isotopic systematics agree with direct incorporation of enriched mantle-derived material into parental melts but variable incorporation of potassium-rich crustal materials is evidenced by highly positive gamma Os 800 Ma values for a sub-suite of Mg–Cr-rich silicocarbonatites, indicating intense fenitization. The highly radiogenic Os isotopic compositions of monzogabbros and a syenite argue for their derivation from crustal lithologies with no or only negligible contribution of mantle material. Collectively, low Ir, Ru, Pt and Pd contents found in the Tamil Nadu carbonatites appear to indicate the incapability to significantly modify the total budget of these elements in the Earth’s mantle during carbonatite metasomatism. In contrast, very high Re/Os ratios found in some of the analyzed carbonatites, paralleled by extremely radiogenic 187Os/188Os signature, can produce large modification of the Re–Os isotopic composition of mantle peridotites during carbonatite melt percolation when high melt/rock ratios are achieved.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10505 - Geology

Projekt

<a href="/cs/project/GA15-08583S" target="_blank" >GA15-08583S: Role karbonatitů pro bilanci HFSE a HSE prvků v zemském plášti - kombinovaný přístup pomocí stabilních a radiogenních izotopů</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2019

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Earth and Planetary Science Letters

ISSN

0012-821X

e-ISSN

—

Svazek periodika

520

Číslo periodika v rámci svazku

August 15

Stát vydavatele periodika

NL - Nizozemsko

Počet stran výsledku

13

Strana od-do

175-187

Kód UT WoS článku

000474502200018

EID výsledku v databázi Scopus

2-s2.0-85067071175