Deep‐tow magnetic anomaly study of the Pacific Jurassic Quiet Zone and implications for the geomagnetic polarity reversal timescale and geomagnetic field behavior

Abstract

[1] The Jurassic Quiet Zone (JQZ) is a region of low-amplitude magnetic anomalies whose distinctive character may be related to geomagnetic field behavior. We collected deep-tow magnetic profiles in Pigafetta Basin (western Pacific) where previous deep-tow data partially covered the JQZ sequence. Our goals were to extend the survey through the JQZ, examine anomaly correlations, and refine a preliminary geomagnetic polarity timescale (GPTS) model. We collected a series of closely spaced profiles over anomaly M34 and Ocean Drilling Program Hole 801C to examine anomaly correlation in detail, one profile in between previous profiles, and two long profiles extending the survey deeper into the JQZ. Anomaly features can be readily correlated except in a region of lowamplitude, short-wavelength anomalies in the middle of the survey area (''low-amplitude zone'' or LAZ). The small multiprofile surveys demonstrate anomaly linearity, implying that surrounding anomalies are also linear and likely result from crustal recording of geomagnetic field changes. We constructed a GPTS model assuming that most anomalies result from polarity reversals. The polarity timescale is similar to the polarity sequences from previous studies, but its global significance is uncertain because of problems correlating anomalies in the LAZ and the ambiguous nature of the small JQZ anomalies. Overall anomaly amplitude decreases with age into the LAZ and then increases again, implying low geomagnetic field strength, perhaps related to a rapidly reversing field. Other factors that may contribute to the LAZ are interference of anomalies over narrow, crustal polarity zones and poorly understood local tectonic complexities.

Friction properties of the plate boundary megathrust beneath the frontal wedge near the Japan Trench: an inference from topographic variation

“…The subducting direction changed from NNW to SSE to WNW to ESE at approximately 46 Ma and has been constant since that time (von Huene and Lallemand 1990). The current age of the Pacific Plate along the Japan Trench is approximately 130 to 140 Ma, as defined by a geomagnetic anomaly (Nakanishi et al 1989;Tominaga et al 2008).…”

Seismic constraints on the processes and consequences of secondary igneous evolution of Pacific oceanic lithosphere

“…The well-defined Japanese, Hawaiian, and Phoenix magnetic lineation sets converge around a region of low-amplitude, short-wavelength magnetic anomalies known as the Jurassic Quiet Zone (JQZ). Recent and ongoing studies in the region have correlated seafloor magnetic anomalies as far back as ~170 Ma Tivey et al, 2006;Tominaga et al, 2008], but the cause of the anomalous nature of the JQZ (i.e., low-amplitude magnetic anomalies combined with rapid field fluctuations) remains unresolved. Cretaceous intraplate volcanism may play a role in obscuring seafloor magnetic records, due to the widespread emplacement of large volumes of igneous material into pre-existing Jurassic crust, and the relationship between seafloor volcanic features and JQZ magnetic anomalies has been considered in previous studies [Kent and Gradstein, 1985;Tivey et al, 2006].…”

“…In this region, the widespread emplacement of large volumes of igneous material into pre-existing Jurassic crust brings into question the relationship between Cretaceous-age seafloor volcanic features and JQZ magnetic anomalies [e.g., Sager et al, 1988, Tivey et al, 2006Tominaga et al, 2008]. We model the structure of modified oceanic crust in the JQZ using MCS images and wide-angle sonobuoy data in order to gauge the impact of Cretaceous magmatism on crustal structure and study how crustal evolution occurs through the transport and emplacement of a large distribution of melt through the lithosphere and into the crust.…”

The Magnetic Field of Planet Earth

“…31). Interestingly, independent indications that this may well have been the case can also be found in marine magnetic anomaly profiles which happen to be particularly weak during the 167-155 Ma time period (e.g., Tivey et al 2006;Tominaga et al 2008). This portion of the magnetic anomaly record, found in the Pacific, displays many small amplitude fluctuations and is known as the Pacific Jurassic Quiet Zone (JQZ in Fig.…”

“…Substantial efforts are currently under way to try and recover similar detailed information about earlier field intensity variations from both sea-surface and nearbottom marine magnetic anomaly profiles (e.g. Pouliquen et al 2001;Bowers et al 2001;Tivey et al 2006;Tominaga et al 2008).…”