U–Th–Pb and Lu–Hf isotopic constraints on the evolution of sub-continental lithospheric mantle, French Massif Central

Tracing the metasomatic and magmatic evolution of continental mantle roots with Sr, Nd, Hf and and Pb isotopes: A case study of Middle Atlas (Morocco) peridotite xenoliths

“…However, high-eHf clinopyroxene separates generally originate from highly infertile harzburgites that are unlikely to participate in mantle melting. Fertile lherzolites, however, seem to maintain coupled Sr-Nd-Hf isotopes indistinguishable from the bulk of oceanic basalts (e.g., Shaw et al, 2007;Wittig et al, 2007).…”

“…In comparison, emerging Nd-Hf isotope data suggests remarkable variation in lithospheric minerals that is distinct from the tightly correlated OIB range in certain, carbonatite/hydrous fluid-metasomatised xenoliths suites (Bizimis et al, , 2007Wittig et al, 2006;Shaw et al, 2007). Therefore, the combination of Hf and Nd isotopes may yield a powerful, although yet to be tested tool in detecting incorporation of SCLM into terrestrial volcanism (Pearson and Nowell, 2002;Wittig et al, 2006Wittig et al, , 2007. However, high-eHf clinopyroxene separates generally originate from highly infertile harzburgites that are unlikely to participate in mantle melting.…”

“…Moreover, Th and U show contrasting behavior during metasomatic enrichment in hydrous and some carbonatitic liquids (Bell and Tilton, 2001) that percolate through the SCLM. As such, hydrous and carbonatitic fluids may result in highly fractionated 232 Th/ 238 U ratios (j) in mantle minerals that are distinctly lower (e.g., Wittig et al, 2007) or higher (this study) than estimates for depleted MORB-mantle (DMM, j $ 2.5) and Bulk Silicate Earth (BSE, j $ 3.4, Galer and O'Nions, 1985). In contrast, percolating silicate melts are less likely to impose fractionated 232 Th/ 238 U on the SCLM and are thought to impart j within the typical range of DMM and BSE.…”

Lu-Hf Isotopic Systematics and Its Applications for Geology

“…Rb-Sr, Sm-Nd 및 U-Pb 동위원소 시스템의 경우, 모원소와 자원소 모두 액상친화적인 원소로 암석권맨틀에서의 이차 변성교대작용동안 쉽게 거동한다 (Downes, 2001;Wittig et al, 2007;Choi and Mukasa, 2012). ReOs 동위원소 시스템의 경우는 맨틀 암석내 Os 농도 가 변성교대작용을 일으키는 매체(예, 함수유체, 탄산 염질 유체 또는 규질 액체 등)보다 약 10-10,000배 정도로 높아서 이차 거동에 대하여 상대적으로 안정 한 편이다 (Walker et al, 1989;Pearson et al, 1995;Reisberg and Lorand, 1995).…”

“…그러나 Re과 Os 같은 백금족원소는 대개 맨틀 암석내 부구성광물 인 황화광물에 농집되어 있어 이들의 이차거동에 매 우 민감하므로 주의가 필요하다 (Gao et al, 2002;Lorand et al, 2013). 최근 연구 결과에 의하면 LuHf 동위원소시스템은 맨틀 내 변성교대작용 동안 쉽 게 거동하지 않으므로 Re-Os법과 교차 활용하면 비 교적 신뢰도 높은 범주의 연대측정이 가능하다고 알 려졌다( Pearson and Nowell, 2003;Lapen et al, 2005;Wittig et al, 2007;Choi et al, 2010;Choi and Mukasa, 2012). 맨틀 단사휘석 내 Lu-Hf 폐쇄온도는 약 900 o C로 추정된다 (Choi et al, 2008;Choi and Mukasa, 2012).…”