TY - JOUR

T1 - Zoned crystal records of transcrustal magma transport, storage and differentiation

T2 - Insights from the shatsky rise oceanic plateau

AU - Van Gerve, Thomas D.

AU - Neave, David A.

AU - Almeev, Renat R.

AU - Holtz, Francois

AU - Namur, Olivier

N1 - Funding Information: This work was supported by the German Research Foundation (DFG; Emmy Noether grant) and the Research Foundation - Flanders (FWO; Odysseus grant) through ON. D.A.N. acknowledges support from the DFG (NE2097/1-1) and the University of Manchester (Presidential Fellowship). F.H. acknowledges support from the DFG (HO1337/35).

PY - 2020/8

Y1 - 2020/8

N2 - Magmatic processes occurring in the deepest parts of sub-volcanic plumbing systems remain poorly constrained. However, crystal mush fragments incorporated into ascending magmas can provide valuable insights into the processes and conditions of transcrustal magma transport, storage and differentiation. Here we use lava samples drilled from Tamu Massif, Shatsky Rise, to understand the magmatic processes taking place in a region of thickened oceanic crust. We observe correlations between crystal textures and compositional zones in plagioclase that reveal relationships between mechanisms of magmatic differentiation and the crustal depths at which they occurred. When combined with geothermobarometric models, our observations indicate that deep crustal crystal storage took place in high-crystallinity mushes at two discrete levels (~17 and ~27km depth). Diffusive constraints from crystal zoning lengthscales indicate that the lifetime of crystals within the mushes exceeded several thousand years. Magmatic recharge was frequent and produced various dissolution textures in plagioclase. In contrast, shallow crystal storage (~2.4 km depth) took place in a liquid-dominated domain where crystal residence times were much shorter. Crystal zoning patterns indicate that magmas transporting crystals from the deepest environment to the surface sometimes accumulated additional crystals from mid-crustal storage regions and sometimes did not, highlighting the complexity of magma assembly processes. Temperature contrasts in the lower crust at Shatsky Rise are probably low, owing to extensive magma input and a paucity of hydrothermal cooling at depth. Crystal growth morphologies are consequently relatively simple. Crystallization in thick and thermally mature crusts may therefore lead to less complexity in crystal textures than crystallization in thinner crusts where temperature contrasts are higher. Our observations indicate that combining thermobarometry with studies of crystal textures and crystal compositions is a powerful approach for improving our understanding of magmatic differentiation and magma ascent paths.

AB - Magmatic processes occurring in the deepest parts of sub-volcanic plumbing systems remain poorly constrained. However, crystal mush fragments incorporated into ascending magmas can provide valuable insights into the processes and conditions of transcrustal magma transport, storage and differentiation. Here we use lava samples drilled from Tamu Massif, Shatsky Rise, to understand the magmatic processes taking place in a region of thickened oceanic crust. We observe correlations between crystal textures and compositional zones in plagioclase that reveal relationships between mechanisms of magmatic differentiation and the crustal depths at which they occurred. When combined with geothermobarometric models, our observations indicate that deep crustal crystal storage took place in high-crystallinity mushes at two discrete levels (~17 and ~27km depth). Diffusive constraints from crystal zoning lengthscales indicate that the lifetime of crystals within the mushes exceeded several thousand years. Magmatic recharge was frequent and produced various dissolution textures in plagioclase. In contrast, shallow crystal storage (~2.4 km depth) took place in a liquid-dominated domain where crystal residence times were much shorter. Crystal zoning patterns indicate that magmas transporting crystals from the deepest environment to the surface sometimes accumulated additional crystals from mid-crustal storage regions and sometimes did not, highlighting the complexity of magma assembly processes. Temperature contrasts in the lower crust at Shatsky Rise are probably low, owing to extensive magma input and a paucity of hydrothermal cooling at depth. Crystal growth morphologies are consequently relatively simple. Crystallization in thick and thermally mature crusts may therefore lead to less complexity in crystal textures than crystallization in thinner crusts where temperature contrasts are higher. Our observations indicate that combining thermobarometry with studies of crystal textures and crystal compositions is a powerful approach for improving our understanding of magmatic differentiation and magma ascent paths.

KW - Crystal mush

KW - Crystal textures

KW - Crystal zoning

KW - Oceanic crust

KW - Plagioclase

UR - http://www.scopus.com/inward/record.url?scp=85099627433&partnerID=8YFLogxK

U2 - 10.1093/petrology/egaa080

DO - 10.1093/petrology/egaa080

M3 - Article

AN - SCOPUS:85099627433

VL - 61

JO - Journal of Petrology

JF - Journal of Petrology

SN - 0022-3530

IS - 8

M1 - egaa080

ER -