X-Ray Diffraction and Chemical Study of Secondary Minerals from Deep Sea Drilling Project Leg 51, Holes 417A and 417D.

Scheidegger, K. F. and Stakes, D. S. (1980) X-Ray Diffraction and Chemical Study of Secondary Minerals from Deep Sea Drilling Project Leg 51, Holes 417A and 417D. Open Access Initial Reports of The Deep Sea Drilling Project, 51/52/53 (Part 2) . pp. 1253-1263. DOI 10.2973/dsdp.proc.515253.150.1980.

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Secondary minerals found in fracture fillings and in fragments of altered
basalt from Holes 417A and 417D were studied by both X-ray
diffraction and chemical techniques. Minerals found in fracture fillings
from Hole 417A are dominated by montmorillonite, "protoceládonite,"
analcite, and lesser saponite; celadonite and ferrosaponite are the characteristic
secondary minerals in Hole 417D fracture fillings. Assuming that
minerals found in such fracture fillings reflect the composition of the
secondary fluids that produced them, it is apparent that those from Hole
417A were dominantly Al-rich, while those from Hole 417D were more
enriched in Fe, Mg, and K. X-ray diffraction study of bulk samples
support such fundamental differences in secondary mineralogy. In addition,
the X-ray data on bulk samples suggest that primary plagioclase is
the feldspar in Hole 417D rocks, and secondary potassium feldspar is the
feldspar in Hole 417A altered rocks.
Using available published data on secondary miner?1" found in other
altered oceanic crust, it is possible to interpret the differences in secondary
mineralogy that exist between the two sites. Secondary minerals
present in Hole 417D rocks are believed to have formed under hydrothermally
influenced, low temperature, nonoxidative diagenesis;
whereas, those present in Hole 417A were produced under similarly low
temperatures, but much more highly oxidizing conditions. The fundamental
differences in secondary mineralogy between the two sites can be
best explained by the accompanying remobilization of elements that involved
plagioclase alteration in Hole 417A rocks. A comparison of the
composition of Hole 417A and 417D secondary minerals with those found
in younger crust suggests that the age of crust, influenced by the changing
conditions of alteration, control the chemistry of secondary minerals
found in available pore spaces in altered rocks. Minerals found in young
crust (<15 m.y.B.P.) are highly Mg-rich; minerals found in crust of
intermediate age (—15-50 m.y.B.P.) are dominantly enriched in Fe and
Mg; and those found in older crust have higher contents of Al and K.

Document Type: Article
Refereed: No
Open Access Journal?: Yes
DOI etc.: 10.2973/dsdp.proc.515253.150.1980
ISSN: 0080-8334
Projects: Enrichment, DSDP
Date Deposited: 14 Feb 2017 14:08
Last Modified: 14 Feb 2017 14:08
URI: http://oceanrep.geomar.de/id/eprint/36528

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