Citation:

j.tecto.2013.07.023

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Abstract:

The location of the seaward tip of a subduction thrust controls material transfer at convergent plate margins, and hence global mass balances. At approximately half of those margins, the material of the subducting plate is completely underthrust so that no accretion or even subduction erosion takes place. Along the remaining margins, material is scraped off the subducting plate and added to the upper plate by frontal accretion. We here examine the physical properties of subducting sediments off Costa Rica and Nankai, type examples for an erosional and an accretionary margin, to investigate which parameters control the level where the frontal thrust cuts into the incoming sediment pile.

A series of rotary-shear experiments to measure the frictional strength of the various lithologies entering the two subduction zones were carried out. Results include the following findings: (1) At Costa Rica, clay-rich strata at the top of the incoming succession have the lowest strength (µres = 0.19) while underlying calcareous ooze, chalk and diatomite are strong (up to µres = 0.43; µpeak = 0.56). Hence the entire sediment package is underthrust. (2) Off Japan, clay-rich deposits within the lower Shikoku Basin inventory are weakest (µres = 0.13–0.19) and favour the frontal proto-thrust to migrate into one particular horizon between sandy, competent turbidites below and ash-bearing mud above. (3) Taking in situ data and earlier geotechnical testing into account, it is suggested that mineralogical composition rather than pore-pressure defines the position of the frontal thrust, which locates in the weakest, clay mineral-rich (up to 85 wt.%) materials. (4) Smectite, the dominant clay mineral phase at either margin, shows rate strengthening and stable sliding in the frontal 50 km of the subduction thrust (0.0001–0.1 mm/s, 0.5–25 MPa effective normal stress). (5) Progressive illitization of smectite cannot explain seismogenesis, because illite-rich samples also show velocity strengthening at the conditions tested.

Project(s):

Deep Sea Drilling Project (DSDP)

Ocean Drilling Program (ODP)

Volatiles and Fluids in Subduction Zones (SFB574)

Funding:

German Research Foundation (DFG), grant/award no. 5484524 : Volatiles and Fluids in Subduction Zones

Coverage:

Median Latitude: 13.078206 * Median Longitude: -112.275867 * South-bound Latitude: 7.921317 * West-bound Longitude: 134.011883 * North-bound Latitude: 31.652517 * East-bound Longitude: -86.179117

Date/Time Start: 1973-07-15T00:00:00 * Date/Time End: 2002-08-22T19:26:00

Minimum DEPTH, sediment/rock: 1.00 m * Maximum DEPTH, sediment/rock: 783.30 m

Event(s):

31-297 * Latitude: 30.872700 * Longitude: 134.164800 * Date/Time: 1973-07-15T00:00:00 * Elevation: -4458.0 m * Penetration: 679.5 m * Recovery: 125 m * Location: North Pacific/Philippine Sea/BASIN * Campaign: * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL) * Comment: 26 cores; 241.5 m cored; 1 m drilled; 51.8 % recovery

138-844 * Latitude: 7.921317 * Longitude: -90.480767 * Date/Time Start: 1991-05-08T00:00:00 * Date/Time End: 1991-05-12T00:00:00 * Elevation: -3414.5 m * Penetration: 514 m * Recovery: 499.3 m * Location: North Pacific Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Composite Core (COMPCORE) * Comment: 52 cores; 490 m cored; 0 m drilled; 101.9% recovery

170-1039 * Latitude: 9.639767 * Longitude: -86.200033 * Date/Time Start: 1996-11-01T00:00:00 * Date/Time End: 1996-11-20T00:00:00 * Elevation: -4352.0 m * Penetration: 1268 m * Recovery: 449 m * Location: Costa Rica subduction complex, North Pacific Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Composite Core (COMPCORE) * Comment: 56 cores; 497.9 m cored; 407 m drilled; 90.2% recovery

Comment:

VS = velocity strengthening, VW = velocity weakening

Parameter(s):

#	Name	Short Name	Unit	Principal Investigator	Method/Device	Comment
1	Event label	Event
2	Sample code/label	Sample label		Kopf, Achim J
3	DEPTH, sediment/rock	Depth sed	m			Geocode
4	Depth comment	Depth comm		Kopf, Achim J		Depth below decollement (mbsf)
5	Opal, biogenic silica	bSiO2	%	Kopf, Achim J
6	Clay minerals	Clay min	%	Kopf, Achim J	X-ray diffraction (XRD)	Total clay, relative abundance in bulk
7	Comment	Comment		Kopf, Achim J	X-ray diffraction (XRD)
8	Quartz	Qz	%	Kopf, Achim J	X-ray diffraction (XRD)	relative abundance in bulk
9	Comment	Comment		Kopf, Achim J	X-ray diffraction (XRD)
10	Plagioclase	Pl	%	Kopf, Achim J	X-ray diffraction (XRD)	relative abundance in bulk
11	Calcite	Cal	%	Kopf, Achim J
12	Comment	Comment		Kopf, Achim J	X-ray diffraction (XRD)
13	Smectite	Sme	%	Kopf, Achim J	X-ray diffraction (XRD)	Abundance of individual clay in bulk
14	Illite	Ill	%	Kopf, Achim J	X-ray diffraction (XRD)	Abundance of individual clay in bulk
15	Chlorite	Chl	%	Kopf, Achim J	X-ray diffraction (XRD)	Abundance of individual clay in bulk, Chlorite (NT) Kaolinite (CR)
16	Sediment type	Sediment		Kopf, Achim J
17	Shear strength	µpeak		Kopf, Achim J	Ring shear experiments
18	Residual friction coefficient	µres		Kopf, Achim J	Ring shear experiments
19	Comment	Comment		Kopf, Achim J		Rate-dependent behaviour

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

449 data points

Data

Download dataset as tab-delimited text — use the following character encoding:

1 Event	2 Sample label	3 Depth sed [m]	4 Depth comm (Depth below decollement (mbsf))	5 bSiO2 [%]	6 Clay min [%] (Total clay, relative abundanc...)	7 Comment (X-ray diffraction (XRD))	8 Qz [%] (relative abundance in bulk, X...)	9 Comment (X-ray diffraction (XRD))	10 Pl [%] (relative abundance in bulk, X...)	11 Cal [%]	12 Comment (X-ray diffraction (XRD))	13 Sme [%] (Abundance of individual clay ...)	14 Ill [%] (Abundance of individual clay ...)	15 Chl [%] (Abundance of individual clay ...)	16 Sediment	17 µpeak (Ring shear experiments)	18 µres (Ring shear experiments)	19 Comment (Rate-dependent behaviour)
31-297	31-297-15-2,113	336.13	n/a		74		14		12	0		19	32	24	clay-rich silty sand		0.52	VSVW
31-297	31-297-16-2,59	354.59	n/a		28		48		23		trace	5	15	8	glass-bearing silt	0.56	0.51	VSVW
31-297	31-297-17-2,114	393.14	n/a		40		34		25	0		17	17	6	silty claystone		0.47	VSVW
31-297	31-297-20-2,83	506.83	n/a		89		0		10		trace	87	1	1	silty clay	0.29	0.23	VS
31-297	31-297-20-2,112	507.12	n/a		64		22		15	0		36	21	8	claystone	0.28	0.17	VS
31-297	31-297-21-3,125	527.75	n/a		79		12		10	0		35	30	13	claystone		0.16	VS
31-297	31-297-22-2,67	554.17	n/a		51		24		25	0		11	30	10	silty clay	0.42	0.34	VSVW
31-297	31-297-22-2,90	554.40	n/a			no bulk powder						9	24	5	claystone		0.13	VS
31-297	31-297-22-2,110	554.60	n/a		44		29		27	0		30	10	4	sand-silt-clay		0.39	VSVW
31-297	31-297-23-3,100	594.00	n/a		74		14		12	0		49	16	9	claystone		0.13	VS
31-297	31-297-24-3,18	621.68	n/a		63		20		17		trace	38	22	3	clayey siltstone		0.47	VSVW
31-297	31-297-25-3,121	651.21	n/a		78		11		11	0		50	22	6	peat/clay-rich sediment		0.47	VSVW
31-297	31-297-25-6,66	655.16	n/a		72		13		15	0		51	17	4	clayey ash		0.53	VSVW
31-297	31-297-26-1,27	666.27	n/a		81		7		12		trace	53	27	1	ash-bearing clay		0.18	VS
31-297	31-297-26-2,51	668.01	n/a		89		2		9	0		88	0	1	ash-rich tuff		0.54	VW
31-297	31-297-26-2,105	668.55	n/a		87		2		11		trace	83	3	1	claystone	0.27	0.20	VS
190-1177	190-1177-1-2,87	302.57	n/a		50		7		14	21		17	20	13	clayey siltstone		0.34	VSVW
190-1177	190-1177-13-CC,10	424.45	n/a		56		3		16	19		25	23	9	silty claystone		0.15	VS
190-1177	190-1177-19-CC,10	482.20	n/a		54		7		12	14		18	25	10	silty claystone		0.20	VS
190-1177	190-1177-20-CC,5	485.00	n/a		49		12		11	22		16	21	12	silty/sandy claystone		0.25	VSVW
190-1177	190-1177-24-5,130	527.70	n/a		80		0		12	8		67	13	0	silty claystone		0.12	VS
190-1177	190-1177-30-2,40	580.40	n/a		60		8		7	0		44	13	3	silty claystone	0.23	0.15	VS
190-1177	190-1177-49-5,48	767.78	n/a		63		12		6	0		46	14	2	silty turbidite	0.51	0.27	VS
190-1177	190-1177-51-2,115	783.30	n/a		42		26		12	8		29	13	0	ash-bearing silt		0.51	VW
170-1039	170-1039-5-2,15	32.15	n/a		43		16		9	3					variegated silty clay	0.42	0.33	VS
170-1039	170-1039-7-1,30	49.80	n/a		34		21		8	7					variegated silty clay	0.40	0.34	VS
170-1039	170-1039-22-6,10	197.90	n/a		35		17		5	2					diatomaceous mud	0.51	0.40	VW
170-1039	170-1039-38-2,5	345.55	n/a		18		5		14	33					nannofossil chalk/mud	0.56	0.40	VSVW
170-1040	170-1040-24-1,120	381.80	10.6	4	70		4		26		trace				variegated clay	0.38	0.28	VS
170-1040	170-1040-36-3,135	500.35	129.15	4		trace	4		4	92					nannofossil chalk	0.46	0.43	VSVW
170-1040	170-1040-42-1,120	554.90	183.7			trace	6		7	87					nannofossil chalk	0.51	0.43	VW
170-1040	170-1040-51-4,103	645.93	274.73	1	80			trace	8	12					variegated clay	0.50	0.35	VS
170-1040	170-1040-51-4,103	645.93			31		1		4	64
M54/2_35		1.00	n/a	2	80		4		16		trace				hemipelagic clay	0.25	0.19	VS
EW0104-02GC		1.00	n/a	7	85		2		13		trace	90	0	10	hemipelagic mud		0.49	VS
EW0104-16GC		1.00	n/a	8		no bulk powder						88	1	11	hemipelagic mud		0.34	VS
EW0104-36PC		1.00	n/a			no bulk powder									silty clay turbidite		0.33	VW
EW0104-24GC		1.00	n/a			no bulk powder								0	calcareous ooze		0.32	VSVW
EW0104-40GC		1.00	n/a	6	83		2		15		trace	90	1	9	silty clay		0.27	VS
138-844	138-844	9.92	n/a												variegated green clay		0.16	VS
138-844	138-844	150.15	n/a												diatom-nannofossil ooze		0.44	VSVW
138-844	138-844	250.10	n/a												diatom-nannofossil ooze		0.60	VW