Some additional observations on inclusions in the granitic rocks of the Sierra Nevada

Abstract

Microgranular quartz diorite and diorite inclusions are widespread in central Sierra Nevada granitoid rocks and are almost exclusively restricted to hornblende‐bearing rocks, most commonly felsic tonalites and mafic granodiorites. Strontium 87/strontium 86 values of the inclusions and host granitoids from individual plutons generally plot on single isochrons that agree closely with previously determined ages. Neodymium 143/neodymium 144 values of five inclusions ranged from 0.51229 to 0.51248 and yield εNd values that correlate closely with values of their respective hosts. The Nd‐Sm and Rb‐Sr systematics indicate that most inclusions were in isotopic equilibrium with enclosing materials at the time of formation. Silica contents of inclusions and granitoids are contiguous, but inclusions generally contain less than, and granitoids more than, 60% SiO2. Linear continuity of the femic oxide and H2O+ trends relative to SiO2 suggests many inclusions formed as concentrations of hydrous mafic minerals. Variation of other major element oxides and trace elements support this inference. The aforementioned data are generally inconsistent with a direct genetic link between the mafic inclusions and the mantle‐derived basalt. However, many initial Sierra Nevada magmas were produced by mixing of mafic, mantle‐derived melts and felsic crustal materials, resulting in isotopically varied tonalitic and granodioritic magmas. Most inclusions thus represent fragmented crystal accumulations of early‐formed, near‐liquidus minerals generated from these previously mixed magmas.

Overlapping Sr–Nd–Hf–O isotopic compositions in Permian mafic enclaves and host granitoids in Alxa Block, NW China: Evidence for crust–mantle interaction and implications for the generation of silicic igneous provinces

“…The similar mineral assemblages and isotopic compositions of the MMEs and host granitoids in both plutons, which are considered further in Section 6.2, are commonly used to indicate that the microgranular enclaves crystallized from coeval, cognate host magmas via accumulation (Dahlquist, 2002;Dodge and Kistler, 1990) or chilled margins processes (Donaire et al, 2005;Esna-Ashari et al, 2011;Pascual et al, 2008). The cumulate model has been criticized because it would not be compatible with the small grain size and the fine-grained margins of many enclaves (Donaire et al, 2005;Esna-Ashari et al, 2011).…”

Mantle-derived arc related mafic enclaves and host orthogneiss from the Shyok Suture Zone of NE Ladakh, India: An evidence of magma-mixing

“…4-9) produces near-linear trends or overlapping pattern suggesting genetic linkage between them, and could be related to the processes of restite unmixing (Chappell et al, 1987), or fractional crystallization (Dodge and Kistler, 1990) or mixing of mafic-felsic magmas (e.g., Castro et al, 1990;Barbarin and Didier, 1992;Perugini et al, 2003;Arvin et al, 2004;Kumar and Rino, 2006). A wide and near-linear compositional range of ME cannot however, be produced as cumulates of OG or restite separation, particularly for the overlapped ME and OG.…”

“…Their origin has been the subject of investigation for over a century right from Lacroix (1890) introducing the term "enclave" to describe fragments of foreign rocks enclosed in homogeneous igneous rock, which has diverse characteristics, implications, and origins. The renewed interest in enclaves and subsequent debate has centered mainly around whether the enclaves are fragments of recrystallized, refractory and residual materials (Chappell et al, 1987;Chen et al, 1989), or they represent cumulate fragments of felsic host (Dodge and Kistler, 1990), or a resultant of felsic-mafic magma-mixing and mingling processes (e.g., Vernon, 1984Vernon, , 1990Barbarin and Didier, 1992;Castro et al, 1990;Arvin et al, 2004;Kumar and Rino, 2006;Kumar, 2010).…”

Cretaceous to Early Tertiary Granites and Magma Mixing in South Korea : Their Spatio-temporal Variations and Tectonic Implications (Multiple Slab Window Model)

“…각 지역의 주요 암 상을 출현 빈도에 따라 나열하면, 옥천분지에는 알칼 리장석화강암, 섬장화강암(syenogranite), 몬조화강암 과 화강섬록암, 영동-광주분지에는 몬조화강암과 섬장 화강암 그리고 경상분지에는 몬조화강암, 섬장화강암, 화강섬록암과 알칼리장석화강암이다 (Jwa, 2002). 경상분지에 분포하는 화강암은 둥근형태의 산점상 심성암체로 천소 관입(마이아롤리틱 정동, 세립질의 미문상조직, 각섬석 지압계)을 하였으며, 각 암체의 지 열역사 해석을 통해 관입 후 빠른 냉각을 겪었던 것으 로 보고되었다 (Shin and Nishimura, 1993;Lee et al, 1995 (Chappell et al, 1987;Chen et al, 1989;Dodge and Kistler, 1990;Barbarin and Didier, 1991;Didier and Barbarin, 1991;Elburg, 1996;Mass et al, 1997). 1998, 2000; 김춘식 외, 1999; 김종선 과 이준동, 2000).…”