Posteruptive Thermal History of the Proterozoic Basaltic North Shore Volcanic Group of the Midcontinent Rift: Evidence from K/Ar Data of Celadonite

Abstract

This study reports three K/Ar ages on celadonite, a dioctahedral K-Fe mica, in the Proterozoic North Shore Volcanic Group (NSVG) of the Midcontinent Rift in northeastern Minnesota. Celadonite formed during beginning posteruptive, low-temperature conditions at temperatures<100°C and with input of meteoric water. K/Ar ages between 1062±16 Ma and 955.0±12 Ma document a remarkably long posteruptive thermal history of >100 myrs in a thick continental basaltic sequence. In the stratigraphically lower part of the NSVG, celadonite formation occurred at 1062±16 Ma in an amygdule or a vesicle filled with celadonite, while another celadonite amygdule in a stratigraphically higher flow was dated at 1039.4±14 Ma. Both flows are overprinted by a later multistage lower zeolite-phyllosilicate facies assemblage (laumontite-albite-corrensite±chlorite±smectite±prehnite±pumpellyite). In the stratigraphically higher part of the sequence, celadonite crystallization at an amygdule rim is followed by upper zeolite facies conditions (stilbite-heulandite-smectite assemblage) and was dated at 955.0±12.4 Ma. The constrained time frame of 107 myrs indicates a long-lived, probably not continuous and locally occurring, posteruptive thermal alteration process. The data suggest that alteration was depth-controlled and temporally and spatially inhomogeneous and implies the progression of the sequence from a close-to-the-surface alteration mode with input of meteoric water to a burial metamorphic mode and with locally occurring hydrothermal activity due to continuous magmatic activity. Volcanism in the Midcontinent Rift system is supposed to have lasted between 1109 Ma and 1083 Ma based on U/Pb zircon ages. The first crystallization of celadonite is recorded in the lower part of the NSVG and occurred ca. 30 myrs after the emplacement of the Silver Bay aplite intrusion in the upper part of the NSVG. Burial rates are determined to be 0.04 km·Ma-1and 0.10 km·Ma-1. The hydrothermal alteration under low-temperature burial conditions clearly postdates the rift-related alkaline and tholeiitic magmatism of the Midcontinent Rift and overlaps with the depositional window of the sedimentary rocks that overlie the Midcontinent Rift volcanics, as well as crustal-scale fault systems that were active during Grenvillian tectonic uplift after the cessation of magmatic activity.

Authigenic Green Mica in Interflow Horizons within Late Cretaceous Deccan Volcanic Province, India and Its Genetic Implications

“…The XRD peaks of celadonite were in good agreement with the results obtained in previous studies [1,2,7,13,14]. The ~3.63 Å and ~3.08 Å peaks corresponding to 112 ̅ and 112, respectively, reflected a well-ordered 1 M mica polymorph [1,3,7,13,61]. The value of d060 spacing of the studied green phyllosilicate (~1.509 Å ) was close to the data (between 1.507-1.509 Å ) formerly reported in the literature for dioctahedral mica; i.e., celadonite [2,5,14].…”

“…The 1.51 Å d060 value was given as a discriminating value by the AIPEA nomenclature [80]. Unlike celadonite, glauconite exhibits reduced hkl reflection and broader basal peaks than celadonite, as well as merged 003 and 022 peaks and d060 spacing less than 1.51 Å [2,3,11,14,[58][59][60][61]84]. Therefore, the X-ray diffraction parameters ruled out glauconite and confirmed the presence of celadonite in both green boles.…”

Sources of Hydrothermal Fluids Inferred from Oxygen and Carbon Isotope Composition of Calcite, Keweenaw Peninsula Native Copper District, Michigan, USA

“…The rift-flanking Jacobsville Sandstone consists of fluvial red-to-white-colored sandstone and was likely deposited during the compressional event in association with the protracted development of the Keweenaw fault. The native copper deposits of the Keweenaw Peninsula were formed during a regional hydrothermal event between about 1070 to 1040 Ma (Figure 3) [30][31][32]. The age of the regional hydrothermal event is corroborated by radiometric dating from the native copper associated main-stage minerals in the main area of the Keweenaw Peninsula native copper district, native copper and associated minerals that cross cut the sedimentary rock hosted chalcocite deposit at the White Pine Mine, and the main metamorphogenic-hydro- The native copper deposits of the Keweenaw Peninsula were formed during a regional hydrothermal event between about 1070 to 1040 Ma (Figure 3) [30][31][32].…”

“…The native copper deposits of the Keweenaw Peninsula were formed during a regional hydrothermal event between about 1070 to 1040 Ma (Figure 3) [30][31][32]. The age of the regional hydrothermal event is corroborated by radiometric dating from the native copper associated main-stage minerals in the main area of the Keweenaw Peninsula native copper district, native copper and associated minerals that cross cut the sedimentary rock hosted chalcocite deposit at the White Pine Mine, and the main metamorphogenic-hydro- The native copper deposits of the Keweenaw Peninsula were formed during a regional hydrothermal event between about 1070 to 1040 Ma (Figure 3) [30][31][32]. The age of the regional hydrothermal event is corroborated by radiometric dating from the native copper associated main-stage minerals in the main area of the Keweenaw Peninsula native copper district, native copper and associated minerals that cross cut the sedimentary rock hosted chalcocite deposit at the White Pine Mine, and the main metamorphogenic-hydrothermal event in the North Shore Volcanic Group.…”

“…A late calcite vein at the White Pine mine was dated at about 1000 to 1040 Ma [32] on the low end of the likely age of main-stage hydrothermal activity in the Keweenaw Peninsula but compatible with a continuous latestage hydrothermal activity. Schmidt [31] dated a paragenetic late mineral assemblage in the North Shore Volcanic Group to be about 945 to 965 Ma; this event occurred well after the main-stage native copper forming event, and if the late-stage of the Keweenaw Peninsula is continuous with the main-stage, then the 945 to 965 Ma event may represent a pulse of hydrothermal activity after the late-stage of the Keweenaw Peninsula and perhaps not yet recognized as being present in the Keweenaw Peninsula.…”