The Shape and Volume of the Skaergaard Intrusion, Greenland: Implications for Mass Balance and Bulk Composition

Nielsen, Thorkild

doi:10.1093/petrology/egg092

Cited by 157 publications

(118 citation statements)

References 43 publications

Supporting

Mentioning

103

Contrasting

Order By: Relevance

“…1 m/year for the po-C unit, decreasing continuously upwards (pomi-C: 0.3 m/ year; pomic-C: 0.1 m/year; pmic-C: 0.06 m/year; pomica-C: 0.02 m/year). However, the rather high crystal accumulation rates, especially for po-C cumulates, contrast with the values commonly accepted for crystal accumulation rate at the floor of mafic layered intrusions (\0.1 m/year; Morse 1979, Sparks et al 1985Nielsen 2004). In the assumption of a high accumulation rate for po-C cumulates (e.g., 1 m/year), compaction cannot be efficient at expelling the intercumulus melt when the residual porosity is lower than 0.22 (Fig.…”

Section: Efficiency Of Compaction and Compositional Convectioncontrasting

confidence: 62%

Efficiency of compaction and compositional convection during mafic crystal mush solidification: the Sept Iles layered intrusion, Canada

Namur

Charlier

2012

Contrib Mineral Petrol

View full text Add to dashboard Cite

Adcumulate formation in mafic layered intrusions is attributed either to gravity-driven compaction, which expels the intercumulus melt out of the crystal matrix, or to compositional convection, which maintains the intercumulus liquid at a constant composition through liquid exchange with the main magma body. These processes are length-scale and time-scale dependent, and application of experimentally derived theoretical formulations to magma chambers is not straightforward. New data from the Sept Iles layered intrusion are presented and constrain the relative efficiency of these processes during solidification of the mafic crystal mush. Troctolites with meso-to ortho-cumulate texture are stratigraphically followed by Fe-Ti oxide-bearing gabbros with adcumulate texture. Calculations of intercumulus liquid fractions based on whole-rock P, Zr, V and Cr contents and detailed plagioclase compositional profiles show that both compaction and compositional convection operate, but their efficiency changes with liquid differentiation. Before saturation of Fe-Ti oxides in the intercumulus liquid, convection is not active due to the stable liquid density distribution within the crystal mush. At this stage, compaction and minor intercumulus liquid crystallization reduce the porosity to 30%. The velocity of liquid expulsion is then too slow compared with the rate of crystal accumulation. Compositional convection starts at Fe-Ti oxide-saturation in the pore melt due to its decreasing density. This process occurs together with crystallization of the intercumulus melt until the residual porosity is less than 10%. Compositional convection is evidenced by external plagioclase rims buffered at An 61 owing to continuous exchange between the intercumulus melt and the main liquid body. The change from a channel flow regime that dominates in troctolites to a porous flow regime in gabbros results from the increasing efficiency of compaction with differentiation due to higher density contrast between the cumulus crystal matrix and the equilibrium melts and to the bottom-up decreasing rate of crystal accumulation in the magma chamber.

show abstract

Section: Efficiency Of Compaction and Compositional Convectioncontrasting

confidence: 62%

Efficiency of compaction and compositional convection during mafic crystal mush solidification: the Sept Iles layered intrusion, Canada

Namur

Charlier

2012

Contrib Mineral Petrol

View full text Add to dashboard Cite

show abstract

“…3c and d), as seen in the aforementioned cumulate gabbros (Turner, 1996;Nielsen, 2004;Zhou et al, 2005Zhou et al, , 2008aZhao et al, 2009;Namur et al, 2011;VanTongeren and Mathez, 2012). Therefore, the low Mg, Cr and Ni concentrations, together with the lack of modal olivine and cumulate textures in all samples, likely denote a non-cumulate origin.…”

Section: Accumulation or Fractional Crystallizationmentioning

confidence: 81%

“…The 1.21 Ga high Fe-Ti gabbros in this study do not show these characteristics. In particular, the Yishui gabbros are alkaline in nature, also inconsistent with most cumulate gabbros that are tholeiitic (Nielsen, 2004;Zhou et al, 2008a,b;Zhao et al, 2009;Namur et al, 2011;VanTongeren and Mathez, 2012). They also do not possess a prominent sub-horizontal igneous lamination defined (Wang et al, 2004.…”

Section: Accumulation or Fractional Crystallizationmentioning

confidence: 87%

“…7b) is inconsistent with this view. Indeed, like the cumulate oceanic gabbros and several well-known layered intrusions with Fe-Ti-rich trends in the world (i.e., the Skaergaard Intrusion in East Greenland, Nielsen, 2004;Jakobsen et al, 2005Jakobsen et al, , 2011; the Sept Iles layered intrusion in Canada, Namur et al, 2011; the Bushveld Complex in South Africa, VanTongeren and Mathez, 2012; the Panzhihua intrusion complex, Zhou et al, 2005Zhou et al, , 2008a,b and the Damiao complex in the NCC, Zhao et al, 2009), they are generally sub-alkaline in composition, and exhibit positive Eu and Sr anomalies. Moreover, structurally, they commonly show cryptic layering.…”

Section: Accumulation or Fractional Crystallizationmentioning

confidence: 99%

“…Moreover, most of the Fe-Ti-rich compositions are found in plutonic environments and only rare cases are known for erupted rocks (Clague et al, 1981;Perfit and Fornari, 1983;Sinton et al, 1983;Hunter and Sparks, 1987;Pearce et al, 1994;Hooper, 2000;Harper, 2003;Zhang et al, 2012). Some of these intrusions host world class Fe-Ti oxide deposits, such as the Skaergaard Intrusion in East Greenland (e.g., Nielsen, 2004;Jakobsen et al, 2005Jakobsen et al, , 2011, the Sept Iles layered intrusion in Canada (e.g., Namur et al, 2011), the Bushveld Complex in South Africa (e.g., VanTongeren and Mathez, 2012), the Panzhihua intrusive complex in southwestern China (e.g., Zhou et al, 2005Zhou et al, , 2008a and the Damiao complex in North China (e.g., Zhao et al, 2009). However, the mechanism by which they achieved their enrichment in Fe-Ti contents, especially for those developed in a continental regime, remains controversial.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mesoproterozoic high Fe–Ti mafic magmatism in western Shandong, North China Craton: Petrogenesis and implications for the final breakup of the Columbia supercontinent

Peng

Wilde

et al. 2013

Precambrian Research

View full text Add to dashboard Cite

Formation of thick stratiform Fe‐Ti oxide layers in layered intrusion and frequent replenishment of fractionated mafic magma: Evidence from the Panzhihua intrusion, SW China

Song

et al. 2013

Geochem Geophys Geosyst

127

View full text Add to dashboard Cite

The Panzhihua intrusion is one of the largest layered intrusions that hosts huge stratiform Fe‐Ti oxide layers in the central part of the Emeishan large igneous province, SW China. Up to 60 m thick stratiform massive Fe‐Ti oxide layers containing ~85 modal% of magnetite and ilmenite and overlying magnetite gabbro compose cyclic units of the Lower Zone of the intrusion. The cyclic units of the Middle Zone consist of magnetite gabbro and overlying gabbro. In these cyclic units, contents of Fe2O3(t), TiO2 and Cr and Fe3+/Ti4+ ratio of the rocks decrease upward, Cr content of magnetite and forsterite percentage of olivine decrease as well. The Upper Zone consists of apatite gabbro characterized by enrichment of incompatible elements (e.g., 12–18 ppm La, 20–28 ppm Y) and increasing of Fe3+/Ti4+ ratio (from 1.3 to 2.3) upward. These features indicate that the Panzhihua intrusion was repeatedly recharged by more primitive magma and evolved magmas had been extracted. Calculations using MELTS indicate that extensive fractionation of olivine and clinopyroxene in deep level resulted in increasing Fe and Ti contents in the magma. When these Fe‐Ti‐enriched magmas were emplaced along the base of the Panzhihua intrusion, Fe‐Ti oxides became an early crystallization phase, leading to a residual magma of lower density. We propose that the unusually thick stratiform Fe‐Ti oxide layers resulted from coupling of gravity settling and sorting of the crystallized Fe‐Ti oxides from Fe‐Ti‐enriched magmas and frequent magma replenishment along the floor of the magma chamber.

show abstract

The Shape and Volume of the Skaergaard Intrusion, Greenland: Implications for Mass Balance and Bulk Composition

Cited by 157 publications

References 43 publications

Efficiency of compaction and compositional convection during mafic crystal mush solidification: the Sept Iles layered intrusion, Canada

Efficiency of compaction and compositional convection during mafic crystal mush solidification: the Sept Iles layered intrusion, Canada

Mesoproterozoic high Fe–Ti mafic magmatism in western Shandong, North China Craton: Petrogenesis and implications for the final breakup of the Columbia supercontinent

Formation of thick stratiform Fe‐Ti oxide layers in layered intrusion and frequent replenishment of fractionated mafic magma: Evidence from the Panzhihua intrusion, SW China

Contact Info

Product

Resources

About