Description The preserved Precambrian crustal record is strongly episodic, and observation that h... more Description The preserved Precambrian crustal record is strongly episodic, and observation that has been attributed to preservational effects or episodic crustal production. These age peaks are associated with juvenile crustal production, voluminous high-temperature volcanism, massive mantle depletion, widespread orogeny and mineralisation, large apparent polar wander velocity spikes, and subsequent paleointensity increases. The impact of these events impinged on the glaciation record, atmospheric and ocean ...
Tertiary diatremes of the Navajo volcanic field brought a wide variety of Proterozoic xenoliths t... more Tertiary diatremes of the Navajo volcanic field brought a wide variety of Proterozoic xenoliths to the surface of the Colorado Plateau. Examination of crustal xenoliths from the Navajo volcanic field diatremes per-mits reconstruction of Proterozoic pressure-temperature (PT) ...
Geochimica et Cosmochimica Acta Supplement, Jul 1, 2008
Although most geologic data clearly point to an onset of modern plate tectonics, at least locally... more Although most geologic data clearly point to an onset of modern plate tectonics, at least locally, by 3 Ga, geodynamic modeling for high mantle temperatures suggests that plate tectonics had several false starts, each followed by a return to stagnant lid tectonics. The distribution of U/Pb zircon ages in granitoids and detrital zircons suggests the last plate-tectonic shutdown may have started about 2.4 Ga and lasted the order 250 My. There is also little Nd or Hf isotope evidence to support significant juvenile additions to the continental ...
Combined field, seismic, xenolith, and heat flow data from the Four Corners region of the Colorad... more Combined field, seismic, xenolith, and heat flow data from the Four Corners region of the Colorado Plateau permit construction of a four-layer crustal model in which a thin sediment layer is underlain sequentially by Early Proterozoic supracrustal rocks and granitoids, intermediate plutonic ...
Mafic xenoliths from the Navajo Volcanic Field (NVF) in the Colorado Plateau are represented by f... more Mafic xenoliths from the Navajo Volcanic Field (NVF) in the Colorado Plateau are represented by four lithologies, in order of decreasing abundance: garnet granulite, amphibolite, gabbro, and pyroxene granulite, Eight geochemical groups are defined based chiefly on REE ...
Proterozoic granitoid xenoliths from the Navajo Volcanic Field (NVF) in the southwestern United S... more Proterozoic granitoid xenoliths from the Navajo Volcanic Field (NVF) in the southwestern United States range in composition from tonalitediorite to granite with the latter greatly dominating. There is no apparent relationship between chemical or isotopic composition and age, ...
Eos Transactions American Geophysical Union, Oct 13, 2009
Although it is well established that orogeny is episodic, the duration, correlation and geographi... more Although it is well established that orogeny is episodic, the duration, correlation and geographic distribution of orogenic episodes is not well constrained. Using large numbers of concordant U/Pb zircon ages from subduction-related granitoids (> 7000), it is now possible to better constrain these variables. Monte Carlo simulation probabilistic histograms of zircon age spectra remove questionable and spurious age peaks, yet
The Tijeras Greenstone of mid-Proterozoic age is comprised of basalt flows and sills interlayered... more The Tijeras Greenstone of mid-Proterozoic age is comprised of basalt flows and sills interlayered with small amounts of potassium-rich felsic volcanic rocks, arkose, and quartzite. The basalts are depleted in light REE ($$[La/Sm] _{N} = 0.3-0.7$$) and appear to have been derived from a depleted mantle source similar in composition to the source of mid-ocean ridge and back-arc basin tholeiites. The greenstone is inter-nreted as a fragment of a basalt field erupted in a continental rift.
In terms of high field strength element ratios Nb/Th, Zr/Nb, Nb/Y and Zr/Y, most basalts from non... more In terms of high field strength element ratios Nb/Th, Zr/Nb, Nb/Y and Zr/Y, most basalts from non-arc type Archean greenstones are similar to oceanic plateau basalts, suggestive of mantle plume sources. A large number of these basalts have ratios similar to primitive mantle composition. Perhaps the Archean mantle was less fractionated than at present and “primitive mantle” comprised much of
... Late Archean and Early Proterozoic mafic dike swarms and rift-related basalts, which are wide... more ... Late Archean and Early Proterozoic mafic dike swarms and rift-related basalts, which are widespread on most Precambrian shields, should be ... CONDIE, KC, and HUNTER, DR, 1976, Trace element geochemistry of Archean granitic rocks from the Barberton region, South Africa ...
Geochemical and geophysical data indicate that the average potash content of young calc-alkaline ... more Geochemical and geophysical data indicate that the average potash content of young calc-alkaline volcanics increases in approximately a linear manner with crustal thickness. If such a relationship existed during the Precambrian, potash contents of early Precambrian ([Formula: see text] billion years) calc-alkaline volcanics in the Canadian Shield indicate that these volcanics were erupted onto a crust that was approximately 10–25 km thick. Since 3–13 km of these volcanics are now exposed, the total thickness of the early Precambrian crust prior to the Kenoran orogeny may have approached or reached presentday crustal thicknesses.
Geochemical and geophysical data indicate that the average potash content of young calc-alkaline ... more Geochemical and geophysical data indicate that the average potash content of young calc-alkaline volcanics increases in approximately a linear manner with crustal thickness. If such a relationship existed during the Precambrian, potash contents of early Precambrian ([Formula: see text] billion years) calc-alkaline volcanics in the Canadian Shield indicate that these volcanics were erupted onto a crust that was approximately 10–25 km thick. Since 3–13 km of these volcanics are now exposed, the total thickness of the early Precambrian crust prior to the Kenoran orogeny may have approached or reached presentday crustal thicknesses.
Analysis of the global distribution of U/Pb ages of both subduction-related granitoids and of det... more Analysis of the global distribution of U/Pb ages of both subduction-related granitoids and of detrital zircons suggests that a widespread reduction in magmatic activity on Earth beginning about 2.45 Ga and lasting for 200–250 My. There are no arc-type greenstones or tonalite–trondhjemite–granodiorite (TTG) suites and only one large igneous province (LIP) reported in this time window. There is little Nd or Hf isotopic evidence to support significant additions to the continental crust at convergent plate margins between ...
Description The preserved Precambrian crustal record is strongly episodic, and observation that h... more Description The preserved Precambrian crustal record is strongly episodic, and observation that has been attributed to preservational effects or episodic crustal production. These age peaks are associated with juvenile crustal production, voluminous high-temperature volcanism, massive mantle depletion, widespread orogeny and mineralisation, large apparent polar wander velocity spikes, and subsequent paleointensity increases. The impact of these events impinged on the glaciation record, atmospheric and ocean ...
Tertiary diatremes of the Navajo volcanic field brought a wide variety of Proterozoic xenoliths t... more Tertiary diatremes of the Navajo volcanic field brought a wide variety of Proterozoic xenoliths to the surface of the Colorado Plateau. Examination of crustal xenoliths from the Navajo volcanic field diatremes per-mits reconstruction of Proterozoic pressure-temperature (PT) ...
Geochimica et Cosmochimica Acta Supplement, Jul 1, 2008
Although most geologic data clearly point to an onset of modern plate tectonics, at least locally... more Although most geologic data clearly point to an onset of modern plate tectonics, at least locally, by 3 Ga, geodynamic modeling for high mantle temperatures suggests that plate tectonics had several false starts, each followed by a return to stagnant lid tectonics. The distribution of U/Pb zircon ages in granitoids and detrital zircons suggests the last plate-tectonic shutdown may have started about 2.4 Ga and lasted the order 250 My. There is also little Nd or Hf isotope evidence to support significant juvenile additions to the continental ...
Combined field, seismic, xenolith, and heat flow data from the Four Corners region of the Colorad... more Combined field, seismic, xenolith, and heat flow data from the Four Corners region of the Colorado Plateau permit construction of a four-layer crustal model in which a thin sediment layer is underlain sequentially by Early Proterozoic supracrustal rocks and granitoids, intermediate plutonic ...
Mafic xenoliths from the Navajo Volcanic Field (NVF) in the Colorado Plateau are represented by f... more Mafic xenoliths from the Navajo Volcanic Field (NVF) in the Colorado Plateau are represented by four lithologies, in order of decreasing abundance: garnet granulite, amphibolite, gabbro, and pyroxene granulite, Eight geochemical groups are defined based chiefly on REE ...
Proterozoic granitoid xenoliths from the Navajo Volcanic Field (NVF) in the southwestern United S... more Proterozoic granitoid xenoliths from the Navajo Volcanic Field (NVF) in the southwestern United States range in composition from tonalitediorite to granite with the latter greatly dominating. There is no apparent relationship between chemical or isotopic composition and age, ...
Eos Transactions American Geophysical Union, Oct 13, 2009
Although it is well established that orogeny is episodic, the duration, correlation and geographi... more Although it is well established that orogeny is episodic, the duration, correlation and geographic distribution of orogenic episodes is not well constrained. Using large numbers of concordant U/Pb zircon ages from subduction-related granitoids (> 7000), it is now possible to better constrain these variables. Monte Carlo simulation probabilistic histograms of zircon age spectra remove questionable and spurious age peaks, yet
The Tijeras Greenstone of mid-Proterozoic age is comprised of basalt flows and sills interlayered... more The Tijeras Greenstone of mid-Proterozoic age is comprised of basalt flows and sills interlayered with small amounts of potassium-rich felsic volcanic rocks, arkose, and quartzite. The basalts are depleted in light REE ($$[La/Sm] _{N} = 0.3-0.7$$) and appear to have been derived from a depleted mantle source similar in composition to the source of mid-ocean ridge and back-arc basin tholeiites. The greenstone is inter-nreted as a fragment of a basalt field erupted in a continental rift.
In terms of high field strength element ratios Nb/Th, Zr/Nb, Nb/Y and Zr/Y, most basalts from non... more In terms of high field strength element ratios Nb/Th, Zr/Nb, Nb/Y and Zr/Y, most basalts from non-arc type Archean greenstones are similar to oceanic plateau basalts, suggestive of mantle plume sources. A large number of these basalts have ratios similar to primitive mantle composition. Perhaps the Archean mantle was less fractionated than at present and “primitive mantle” comprised much of
... Late Archean and Early Proterozoic mafic dike swarms and rift-related basalts, which are wide... more ... Late Archean and Early Proterozoic mafic dike swarms and rift-related basalts, which are widespread on most Precambrian shields, should be ... CONDIE, KC, and HUNTER, DR, 1976, Trace element geochemistry of Archean granitic rocks from the Barberton region, South Africa ...
Geochemical and geophysical data indicate that the average potash content of young calc-alkaline ... more Geochemical and geophysical data indicate that the average potash content of young calc-alkaline volcanics increases in approximately a linear manner with crustal thickness. If such a relationship existed during the Precambrian, potash contents of early Precambrian ([Formula: see text] billion years) calc-alkaline volcanics in the Canadian Shield indicate that these volcanics were erupted onto a crust that was approximately 10–25 km thick. Since 3–13 km of these volcanics are now exposed, the total thickness of the early Precambrian crust prior to the Kenoran orogeny may have approached or reached presentday crustal thicknesses.
Geochemical and geophysical data indicate that the average potash content of young calc-alkaline ... more Geochemical and geophysical data indicate that the average potash content of young calc-alkaline volcanics increases in approximately a linear manner with crustal thickness. If such a relationship existed during the Precambrian, potash contents of early Precambrian ([Formula: see text] billion years) calc-alkaline volcanics in the Canadian Shield indicate that these volcanics were erupted onto a crust that was approximately 10–25 km thick. Since 3–13 km of these volcanics are now exposed, the total thickness of the early Precambrian crust prior to the Kenoran orogeny may have approached or reached presentday crustal thicknesses.
Analysis of the global distribution of U/Pb ages of both subduction-related granitoids and of det... more Analysis of the global distribution of U/Pb ages of both subduction-related granitoids and of detrital zircons suggests that a widespread reduction in magmatic activity on Earth beginning about 2.45 Ga and lasting for 200–250 My. There are no arc-type greenstones or tonalite–trondhjemite–granodiorite (TTG) suites and only one large igneous province (LIP) reported in this time window. There is little Nd or Hf isotopic evidence to support significant additions to the continental crust at convergent plate margins between ...
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