Geochemistry and petrogenesis of early Proterozoic amphibolites, west-central Colorado, U.S.A.

Knoper, Michael; Condie, Kent C.

doi:10.1016/0009-2541(88)90129-5

Cited by 66 publications

(48 citation statements)

References 38 publications

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“…9) may be used to evaluate melting or differentiation processes of the mantle (Rajamani et al, 1985;Knoper and Condie, 1988). Fractional crystallisation and batch melting trajectories are distinguished on these diagrams of compatible (Cr) and incompatible elements (Zr N ).…”

Section: Trace Element Modelling and Petrogenesismentioning

confidence: 99%

Geochemistry and petrogenesis of Neoarchaean high-Mg low-Ti mafic igneous rocks in an intracratonic setting, Central India craton: Evidence for boninite magmatism

Srivastava

2006

Geochem. J.

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The southern Central India craton (also known as Bastar craton) has experienced several episodes of mafic magmatism during the early Precambrian time. These mafic igneous rocks are emplaced as dyke and volcanic rocks. A set of mafic dyke swarm and few exposures of mafic volcanics, both emplaced in the Neoarchaean time, contain high-SiO 2 (>52 wt%), high-MgO (>8 wt%), and low-TiO 2 (mostly <0.5 wt%) and classified as boninites on IUGS classification scheme. Al 2 O 3 / CaO ratio classifies these high-Mg mafic igneous rocks into high-Ca and low-Ca (Type 3) boninites. High-Ca boninites show typical boninitic geochemical characteristics, whereas low-Ca variety shows geochemical characteristics similar to the high-Mg norites. Siliceous high-magnesium basalts (SHMB) show similar geochemical properties as observed for the high-Mg norites. Early Precambrian high-Mg norites are reported from the rift setting environment but, on the other hand, boninitic magmatism represents an enigmatic style of magmatism and commonly formed at convergent margin settings. Most boninites are Phanerozoic in age and rarely reported from the Archaean terrains. The established geological and tectonic setting of the Archaean Bastar craton clearly suggests existence of a stable continental rift environment in the region since the Archaean time. Thus, report of Neoarchaean boninite-like rocks in an intracratonic setting is an important feature noticed in the Archaean terrain of Indian peninsula. A highly refractory mantle source region is required to form boninitic magma. Refractory lithosphere may be result of extensive extraction of mafic magma during Mesoarchaean. The preservation of refractory reservoir beneath the Bastar craton for long period of time corroborates a high degree of crustal stability during the Meso-Neoarchaean time. Trace element modelling suggests that high-Mg mafic igneous rocks under study are product of different pulses of boninitic magma produced by ~20-25% melting of a refractory mantle source.

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Section: Trace Element Modelling and Petrogenesismentioning

confidence: 99%

Geochemistry and petrogenesis of Neoarchaean high-Mg low-Ti mafic igneous rocks in an intracratonic setting, Central India craton: Evidence for boninite magmatism

Srivastava

2006

Geochem. J.

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“…[32] Similar magnetite-bearing quartzites associated with mafic metavolcanic rocks have been interpreted as metacherts or cherty iron formations from several localities throughout the Colorado province, including near Gunnison [Condie and Nuter, 1981;Knoper and Condie, 1988], Salida [Boardman, 1986], and in the Green Mountain Formation [Condie and Shadel, 1984]. All of these quartzites differ significantly in character and mineralogy from Proterozoic continental shelf deposits reported from Colorado and New Mexico.…”

Section: Metachert (Quartzite)mentioning

confidence: 85%

“…The southern boundary separating the Colorado/Yavapai province from the circa 1.65 Ga Mazatzal province [Karlstrom and Bowring, 1988] is a northeast trending diffuse zone that extends from southern Arizona to central Colorado [Bennett and DePaolo, 1987;Reed et al, 1987;Shaw and Karlstrom, 1999;Karlstrom et al, 2002]. Geochronologic, geochemical, xenolith, and structural data suggest that this boundary was initially a north dipping subduction zone [e.g., Reed et al, 1987;Knoper and Condie, 1988;Selverstone et al, 1999;Shaw and Karlstrom, 1999], but seismic data have been used to argue for a south dipping structure .…”

Section: Overviewmentioning

confidence: 99%

“…[3] Geochemical data from metavolcanic and metasedimentary rocks within the Early Proterozoic terranes of the southwestern United States are generally interpreted to represent arc, backarc, and intra-arc deposits [Condie and Martel, 1983;Reed et al, 1987;Bickford and Boardman, 1984;Boardman and Condie, 1986;Knoper and Condie, 1988;Premo and Loucks, 2000]. Taken together, these data have been used to argue that southward growth of Laurentia occurred via successive accretion of island arc/backarc terranes onto the Archean craton along multiple subduction zones [e.g., Hills and Houston, 1979;Condie, 1982;Karlstrom and Houston, 1984;Reed et al, 1987;Knoper and Condie, 1988;Houston et al, 1989;Van Schmus et al, 1993].…”

Section: Introductionmentioning

confidence: 99%

“…Taken together, these data have been used to argue that southward growth of Laurentia occurred via successive accretion of island arc/backarc terranes onto the Archean craton along multiple subduction zones [e.g., Hills and Houston, 1979;Condie, 1982;Karlstrom and Houston, 1984;Reed et al, 1987;Knoper and Condie, 1988;Houston et al, 1989;Van Schmus et al, 1993].…”

Section: Introductionmentioning

confidence: 99%

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Early Proterozoic oceanic crust in the northern Colorado Front Range: Implications for crustal growth and initiation of basement faults

Cavosie¹,

Selverstone

2003

Tectonics

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Early Proterozoic oceanic crust exposed in a shear zone in the northern Colorado Front Range provides insight into the tectonic evolution of the Colorado province. Tectonically intermingled mylonitic amphibolite (locally pillowed), metagabbro, clinopyroxenite, metachert, and mélange are preserved within the Buckhorn Creek shear zone west of Fort Collins. Whole rock geochemical data support formation of the igneous protoliths in an oceanic environment. Major and trace element data overlap samples from modern oceanic ridges, and are distinct from modern arc trends. Metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes; core and mantle microstructures indicate initial deformation at temperatures >900°C. Secondary amphiboles define both subhorizontal and subvertical lineations. Kinematic analysis indicates that the rocks experienced E‐W strike‐slip deformation prior to and during amphibolite‐facies metamorphism, followed by N‐S shortening. 40Ar/39Ar data from secondary hornblende yield age steps as old as 1.9 Ga. Based on the chemical data and kinematic evidence for strike‐slip deformation, we propose that the Buckhorn Creek rocks originated at an oceanic ridge‐transform intersection. The high‐T pyroxene fabrics formed during ocean floor deformation prior to 1.7 Ga regional deformation of the Colorado province. The Buckhorn Creek fragment likely represents original oceanic basement for 1.8–1.7 Ga arc magmatism and sedimentation that ultimately formed the Colorado province continental crust. Reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in Colorado. Once formed, subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long‐lived crustal discontinuities.

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Origin of geochemical mantle components: Role of spreading ridges and thermal evolution of mantle

Kimura

Gill

Keken

et al. 2017

Geochem Geophys Geosyst

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We explore the element redistribution at mid-ocean ridges (MOR) using a numerical model to evaluate the role of decompression melting of the mantle in Earth's geochemical cycle, with focus on the formation of the depleted mantle component. Our model uses a trace element mass balance based on an internally consistent thermodynamic-petrologic computation to explain the composition of MOR basalt (MORB) and residual peridotite. Model results for MORB-like basalts from 3.5 to 0 Ga indicate a high mantle potential temperature (T p ) of 1650-15008C during 3.5-1.5 Ga before decreasing gradually to 13008C today. The source mantle composition changed from primitive (PM) to depleted as T p decreased, but this source mantle is variable with an early depleted reservoir (EDR) mantle periodically present. We examine a twostage Sr-Nd-Hf-Pb isotopic evolution of mantle residues from melting of PM or EDR at MORs. At high-T p (3.5-1.5 Ga), the MOR process formed extremely depleted DMM. This coincided with formation of the majority of the continental crust, the subcontinental lithospheric mantle, and the enriched mantle components formed at subduction zones and now found in OIB. During cooler mantle conditions (1.5-0 Ga), the MOR process formed most of the modern ocean basin DMM. Changes in the mode of mantle convection from vigorous deep mantle recharge before 1.5 Ga to less vigorous afterward is suggested to explain the thermochemical mantle evolution.

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Geochemistry and petrogenesis of early Proterozoic amphibolites, west-central Colorado, U.S.A.

Cited by 66 publications

References 38 publications

Geochemistry and petrogenesis of Neoarchaean high-Mg low-Ti mafic igneous rocks in an intracratonic setting, Central India craton: Evidence for boninite magmatism

Geochemistry and petrogenesis of Neoarchaean high-Mg low-Ti mafic igneous rocks in an intracratonic setting, Central India craton: Evidence for boninite magmatism

Early Proterozoic oceanic crust in the northern Colorado Front Range: Implications for crustal growth and initiation of basement faults

Origin of geochemical mantle components: Role of spreading ridges and thermal evolution of mantle

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