Early establishment of seafloor hydrothermal systems during structural extension: paleomagnetic evidence from the Troodos ophiolite, Cyprus

Varga, Robert J.; Gee, Jeffrey S.; Bettison-Varga, Lori; Anderson, Robert S.; Johnson, Cari L.

doi:10.1016/s0012-821x(99)00147-8

Cited by 40 publications

(44 citation statements)

References 42 publications

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“…Great circle depicts average dike orientation measured for 14 samples, 047°/72°SE. remanence directions from dikes in Troodos can alternatively be restored using a sequence of rotations constrained by the geologic history of the ophiolite [Varga et al, 1999]. Similarly, a single rotation solution is not geologically plausible in the case of sheeted dikes exposed at Pito Deep Rift, as it likely averages over distinct structural events that give rise to the net rotational history.…”

Section: Structural Rotation Modelsmentioning

confidence: 99%

“…No amount of rotation about one of these single axes alone restores the remanence direction, so at least two of these proposed rotations must have occurred. We can create a series of rotation models based on the geologic relationships outlined above using 1°incremental amounts of rotation along these paths by using a similar strategy for restoration of remanence directions as Varga et al [1999], and remove rotations in reverse order of formation (the most recent rotation affecting the remanence directions should be removed first followed by older rotations, in a reverse sequential order). If we assume secular variation has been successfully averaged, then the initial, expected remanence direction should be near the GAD direction (000°/−40.2°).…”

Section: Structural Rotation Modelsmentioning

confidence: 99%

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Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

Horst¹,

Gee²,

Karson³

2011

J. Geophys. Res.

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[1] The uppermost oceanic crust produced at the superfast spreading (∼142 km Ma −1 , full-spreading rate) southern East Pacific Rise (EPR) during the Gauss Chron is exposed in a tectonic window along the northeastern wall of the Pito Deep Rift. Paleomagnetic analysis of fully oriented dike (62) and gabbro (5) samples from two adjacent study areas yield bootstrapped mean remanence directions of 38.9°± 8.1°, −16.7°± 15.6°, n = 23 (Area A) and 30.4°± 8.0°, −25.1°± 12.9°, n = 44 (Area B), both are significantly distinct from the Geocentric Axial Dipole expected direction at 23°S. Regional tectonics and outcrop-scale structural data combined with bootstrapped remanence directions constrain models that involve a sequence of three rotations that result in dikes restored to subvertical orientations related to (1) inward-tilting of crustal blocks during spreading (Area A = 11°, Area B = 22°), (2) clockwise, vertical-axis rotation of the Easter Microplate (A = 46°, B = 44°), and (3) block tilting at Pito Deep Rift (A = 21°, B = 10°). These data support a structural model for accretion at the southern EPR in which outcrop-scale faulting and block rotation accommodates spreading-related subaxial subsidence that is generally less than that observed in crust generated at a fast spreading rate exposed at Hess Deep Rift. These data also support previous estimates for the clockwise rotation of crust adjacent to the Easter Microplate. Dike sample natural remanent magnetization (NRM) has an arithmetic mean of 5.96 A/m ± 3.76, which suggests that they significantly contribute to observed magnetic anomalies from fast-to superfast-spread crust.

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Section: Structural Rotation Modelsmentioning

confidence: 99%

Section: Structural Rotation Modelsmentioning

confidence: 99%

Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

Horst¹,

Gee²,

Karson³

2011

J. Geophys. Res.

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“…Paleomagnetic investigations, combined with other geophysical analytical methods, have provided useful information on the kinematics of orogenic regions such as the distribution and amount of vertical-axis rotation of thrust sheets (e.g., Channell, 1992;Channell et al, 1992), oroclinal bending (e.g., Lucente and Speranza, 2001;Schill et al, 2002), horizontal-axis tilting of intrusive rocks (e.g., Varga et al, 1999) and latitudinal displacements and rotations of allochthonous terranes (e.g., Beck, 1980;Irving et al, 1985;Hagstrum and Murchey, 1993). Partial to complete remagnetization of rocks, however, is common in orogenic settings, and can often obliterate primary components (i.e., remanent magnetizations acquired during or soon after deposition for sedimentary rocks).…”

Section: Introductionmentioning

confidence: 99%

Late Miocene remagnetization within the internal sector of the Northern Apennines, Italy

2004

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Paleomagnetic and geologic evidence indicates that Upper Jurassic radiolarian cherts of both the Tuscan Cherts Formation (continental margin, Tuscan Units) and the Monte Alpe Cherts Formation (oceanic crust, Ligurian Units) were remagnetized during Miocene orogenesis of the Northern Apennines of Italy. Characteristic overprint magnetizations with reversed polarities have been found over a large area within the internal sector of the Northern Apennines, including eastern Liguria, Elba Island and the Thyrrenian margin, and west of the Middle Tuscan Ridge. The reversed-polarity overprint (average direction: D = 177j, I = À 52j, a 95 = 15j) was most likely acquired during Late Miocene uplift and denudation of the orogenic chain, and thermochemical remagnetization was a probable consequence of increased circulation of orogenic fluids. Similarly, mostly reversed-polarity directions of magnetization have been found by other workers in overlying post-orogenic Messinian sediments (D = 177j, I = À 57j, a 95 = 3j), which show little counterclockwise (CCW) vertical-axis rotation with respect to stable Europe ( À 8 F 5j). The Monte Alpe Cherts sampled at sites in the external sector of the Northern Apennines, close to major tectonic features, have normal-polarity overprint directions with in situ W -SW declinations. Since the overlying post-orogenic Messinian sediments have not been substantially rotated about vertical axes, the evidence points to an earlier, pre-Late Miocene remagnetization in the external parts of the orogenic chain. D

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“…The western province displays near vertical K 1 directions while the eastern province reveals shallow N-S directions. Large offset normal faulting with rotated blocks at the Solea graben and hydrothermal massive sulfide bodies suggest that spreading rate was slow to intermediate (full spreading rate of 20 to 75 mm/yr [Hurst et al, 1994;Small, 1998;Varga et al, 1999]). Assuming this range of spreading rates, these 10 to 15 km wide provinces of nearly uniform magma flow (Figure 1) represent minimal time intervals of 0.3 to 1 Myr.…”

Section: Discussionmentioning

confidence: 99%

Direct evidence for dynamic magma supply fossilized in the lower oceanic crust of the Troodos ophiolite

Granot

Abelson

Ron

et al. 2011

Geophys. Res. Lett.

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Temporal and spatial variabilities of mantle upwelling and melt supply in mid‐ocean ridges (MORs) have long been documented. Such variabilities span a range of scales and have a profound effect on the structure as well as the composition of the oceanic crust. Previous seismic and gravity studies have suggested that the lower oceanic crust plays a major role in accommodating these changes in melt supply. Here we report the first direct evidence for a sharp transition from coherent sub‐horizontal to near vertical magma flows frozen in the lower oceanic crust of the Troodos ophiolite at the segment edge near a fossil ridge‐transform intersection. We constrain the preferred petrofabric lineation directions at 13 gabbroic sites using anisotropy of magnetic susceptibility (AMS) verified by electron backscatter diffraction. Pre‐emplacement accretion‐related rotations were corrected using magnetic remanence directions. We identify two provinces of nearly uniform susceptibility directions (principal axes) and attribute them to two magmatic episodes. A more focused mantle upwelling and melting episode near the segment midpoint may have resulted in lower crustal lateral magma flows along the fossil segment‐edge, whereas uniform mantle upwelling and melt supply along the entire axis may have resulted in vertical magma flows at the segment‐edge. Overall, our data verify the vital role of the lower oceanic crust in accommodating changes in mantle upwelling and melt supply beneath MORs.

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Early establishment of seafloor hydrothermal systems during structural extension: paleomagnetic evidence from the Troodos ophiolite, Cyprus

Cited by 40 publications

References 42 publications

Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

Paleomagnetic constraints on deformation of superfast-spread oceanic crust exposed at Pito Deep Rift

Late Miocene remagnetization within the internal sector of the Northern Apennines, Italy

Direct evidence for dynamic magma supply fossilized in the lower oceanic crust of the Troodos ophiolite

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