7/31/2019 Silicic-to-bimodal-oligocene-volcanism-in-the-Zimapn-area-Hidalgo-Mexico-USGS-2012

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SILICIC TO BIMODAL OLIGOCENE VOLCANISM IN THE ZIMAPANAREA, MEXICO:STRATIGRAPHY, AGE AND DEFORMATION

*Violeta Mirthala Reyes-Orozco2, Teresa Orozco-Esquivel1, Luca Ferrari Pedraglio1, Fernando Velasco-Tapia2, Margarita Lpez-Martnez3

1Centro de Geociencias, UNAM2Facultad de Ciencias de la Tierra, UANL

3CICESE* reyvi11_11@hotmail.com

INTRODUCTION

We report new field, petrographic and geochronological data for a voluminous sequence of rhyolitic tuffs and domes associated with basaltic to andesitic lavas exposed southwest ofZimapn, state of Hidalgo. The scare geologic studies in the area assigned this sequence to the initial activity of the Transmexican Volcanic Belt (TMVB) in the late Miocene. Based onthis age, normal faults affecting the western part of the study rea (Aljibes half-graben) were considered part of the TMVB intra-arc extension (Suter et al., 1995).

The oldest volcanic unit of the Zimapan sequence consists of unconsolidated, partly reworked rhyolitic tuffs dated at 31.5 Ma (U-Pb, zircon; with a significant antecryst population from 37to 30 Ma). This succession is intruded and partly overlain by mafic laccoliths, sills and dikes that in some places reached the surface forming lava flows that cover both the tuffs and theCretaceous basement. This mafic unit is undated but can be constrained by the overlying silicic unit. This consists of an ignimbrites succession up to 250 m in thickness, probablyemplaced through fissures as indicated by the presence of WNW- ESE striking pyroclastic dikes. A series of partly aligned rhyolitic domes cap the succession. The ignimbrites yielded U-Pb ages of 32.9 and 32.8 Ma (with individual ages ranging from 37 to 28 Ma). Four ages obtained for the rhyolitic domes and dikes range between 28.3 Ma and 31.6 Ma.

Figure 7. a) TAS classification diagram Na2O

Baragar (1971), b) classification diagram based o

terns normalized to chondrites (Anders and Gr

A)

B)

ZIM-48

ZIM-46

A)

ZIM-38 RHYOLITE

RHYOLITIC IGNIMBRITE

RHYOLITIC TUFF

Figure 8. a) U / Pb dating of samples ZIM-38, gram, b) results of Ar / Ar analysis of plagioclasof 27.82 0.22Ma, c) results of Ar / Ar analysisanidine age spectra with a plateau age 31.60isochron age . The numbers close to the ellipse

The Oligocene succession exposed southwe150 m and up to 40 tilting. Rhyolitic domes anGrowth faults and decreasing tilting upsectionunit in the area are untilted Ol-basaltic lava floOur new data show that the volcanic sequenccanism. Although small E-W striking faults doolder and cannot be part of the TMVB intra-ar

Anders, E., Grevesse, N., 1989 .Abundances oIrvine T.N. and Baraga r W.R.A., 1971.A guideLe Bas, M.J., La Maitre, R.W., Streckeisen, Aof Petrology 27, 745-750.Sun, S., McDonough, W., 1989. Chemical anLondon. Special Publication. 42. pags. 313-345Suter M., Carrillo, M. M., Lopz, M. M. y Farrathe basin and range Province, Mexico. GSATera, F., Wasserburg, G., 1972. U-Th-Pb syste(1). pags. 36-51.Wetherill, G., 1956. Discordant uranium-lead aWinchester J.A. and Floyd P.A., 1977. Geoc

Geol., 20, 325-343.

Rhyolitictuff outcroppingto theeastof Cerro El Varal (ZIM-35) withquartz hypidiomorphic toxenomorphic quartz crystals (400 to850 microns), biotite with a fibroushabit(230 microns)andplagioclase(450microns)in aglassymatrix.

A)

B)

C)

RHYOLITICTUFFS

Figure1. a)Outcropof tiltedrhyoliticignimbrite(40)at thebase of Cerro El Varal with aphanitic fine volcanic lithicand sediment tothe groundof Varal Hill (ZIM-40, 2037.268' N/ 9921,963' W), b)Rhyolitictuff handsamplefromsameoutcrop,c)Thinsectionof rhyolitictuff.

D)CERROELVARAL

Mafic

dike

rhyolitictuff

Basalt andesite(ZIM-33) withporphy-ritic texture containigxenomorphicolivine (400-800 microns) in amircolithicmatrixof albite, augiteandopaque.

A)

B)

C)

BASALTICTOANDESITICLAVAS

Figure 2. a) The tuffs are cut by mafic dikes of basaltic-andesitic composition, which in part conducted the magmatothesurfacetofromlavaflowsequenceslikethatfoundatthetop of CerroEl Varal (Fig. 2d), c)Handsampleshowingaphanitic texture, andthepresencealteredolivine crystals.d) Cerro El Varal is formed by massive tilted basaltic-andesiticlaccoliths, wishintrudegreenishrhyolitictuffsthatareseenatthebottomrightoftheimage.

LOCALGEOLOGY

Rhyolitic ignimbrite (ZIM-33) to the NEof Zimapndam.Containxenomorphicquartz (50to 460microns),xenomorphicalbite with polysynthetic twinning(820microns) and biotite with f ibrous habit(320to580microns)in aglassymatrix.

A)

B)

C)

RHYOLITICIGNIMBRITESEQUENCE

Figure 3. a) Ignimbrite, b) Hand sample of a rhyolitic ignimbrite,c) Thin section of cristal-rich rhyolitic ignimbrite.

Rhyoliticdike

Rhyoliticdome

Rhyolite (ZIM-37) to the NE of t heZimapn dam. Porphyritic texture.with hypidiomorphic quartz (760m)and xenomorphic plagioclase(600m),phenocrysts porphyritic in amicrolithicmatrix..

A)

B)

C)

D)

RHYOLITICDOMES

Figure 4. a) Rhyolitic dike intrudingthe ignimbritesequence, andareconsideredas feeders of rhyolitic domes (ZIM38, 20. 67729N/99. 47381 W), b) rhyolite dome to the west of Coaxithi vi llage(2040.406' N / 9924.523' W), c)rhyoliticrocksamplewithflowbanding taken from Cerro San Antonio (20 43.237' N / 9930.873' W),d) Thin section of a rhyolitic lava sample withphenocrystsof quartzand plagioclase.

Basalt(ZIM-44)oftheMesaLlanoSegundocontaining xenomorphicoliv-

inephenocrysts(~1315microns).Withiddingsiticrims,serialporphyritic

textureandmatrixcomposedbyplagioclasemicrolites,feldspar,oliv-

ine,cliopiroxeneandopaque.

A)

B)

C)

D)

BasaltIgnimbrite

OL-BASALTLAVAFLOWS

Figure5. a)Tilted ignimbritepackagediscordantlycoveredbya horizontalbasaltplateau,b)li ghtgraybasalt withaphanitic texture andfresholivine,plagioclaseand pyroxene (20 38.580' N/ 9927.442' W),overlying lacustrinetuffaceousdepos-its c) Hand sampleof ol-basalt,d)Thinsection ofol-basaltlava withaphanitictextureabdfresh oliv-ine,plagioclaseandpyroxene.

horizontal basaltplateau

Titlted basaltic-andesiticlava flow and rhyolitic ignim-brite sequence

Tilted basaltic-andesitic laccolith intrudinga rhyolitic tuff sequence

A)

MESADELEN

C.SAN

ANTONIO

C. LAS PILETAS

C. EL VARAL

C.SONTHE

ZIMAPN

AGUAS

BLANCAS

N

DOMOS RIOLTICOS

BASCULAMIENTO

42

BASCULAMIENTO

43

2044'

2036'

9932'9920'

B)

STRUCTURALGEOLOGY

Figure 6. a) Stereographic projection showing NW-SE pseudo-stratification of a tilted ignimbritesequence dipping 15- 35, with the same orientation measured normal faults, b) Digital eleva-tion model of the study area showing the alignment of rhyolite domes related to its emplacementthrough listric normal growth faults.

E

RA

COLUMNAPISO

POCA

PERODO

ERA

COLUMNAPISO

POCA

PERODO

1.681.68

5.15.1

0.010.01

MaMa

C

E

N

O

Z

O

I

C

O

C

E

N

O

Z

O

I

C

O

SUPERIORSUPERIOR

PLIOCENOPLIOCENO

HOLOCENOHOLOCENO

PLEISTOCENOPLEISTOCENO

M

IO

C

EN

O

M

IO

C

EN

O

N

E

G

E

N

O

N

E

G

E

N

O

24.024.0

55.0

67.0

36.0

71.5

55.0

67.0

36.0

71.5

83.0

86.0

89.0

91.0

97.5

83.0

86.0

89.0

91.0

97.5

108.5108.5

INFERIORINFERIOR

MAASTRICHTIANO

EOCENO

PALEGENO

OLIGOCENO

PALEOCENO

MAASTRICHTIANO

EOCENO

PALEGENO

OLIGOCENO

PALEOCENO

FLANGLOMERADOELMORRO

M

ESOZO

ICO

SU

PERIOR

INFERIOR

SENONIANO

CENOMANIANO

ALBIANO

TURONIANO

CONIACIANO

SANTONIANO

CAMPANIANO

C

R

E

T

C

IC

O

M

ESOZO

ICO

SU

PERIOR

INFERIOR

SENONIANO

CENOMANIANO

ALBIANO

TURONIANO

CONIACIANO

SANTONIANO

CAMPANIANO

C

R

E

T

C

IC

OFM. SOYATAL

FM.

ELDOCTOR

TOBARIOLTICAYETHAY

IGNIMBRITA RIOLTICACARRIZAL

ANDESITA-BASLTICAXINDH

RIOLITAPONTIHU

BASALTO SAUCILLO

CONGLOMERADOPOLMICTICO

COLUVIN

Y

ALUVIN

Faultpseudo-stratification

Rhyolitic Domes

ZIMAPNFALLA

SAN

ANT

ONIO

ZIM - 31

ZIM - 30

ZIM - 47

ZIM - 4

8

33

ZIM - 33

ZI

M - 34ZIM - 35

ZIM - 36

12

15

18

ZI

M - 29

ZIM - 46

ZIM - 28

ZIM - 37ZIM - 38

18

1433

Z

IM - 49

15

20

27

30

20

32

43

ZIM - 4520

ZI

M - 50

ZI

M - 44

ZIM - 43

20

ZI

M - 41ZIM - 4

2

ZIM - 4

0

ZIM - 39

20

1010

ZIM - 24

ZI

M - 25

ZIM - 23

ZIM - 2

2

El Arbolito

El Plan

La Lajita

Loma Bon i ta

El Charco

Mesade Len

Tzibanza

La Sabina

C. EL LE N

Bella Vistadel Ro

Mesa Santa Ines

Carricillo

El Yeso

C. CHINFI

KLIPPE PICACHO

CABALGADURASANTA

INS

CABALGADURA MESA DE LEN

B-A

R

B-A

N

20 36' N 20 36' N

20 37' N 20 37' N

20 38' N 20 38' N

20 39' N 20 39' N

20 40' N 20 40' N

20 41' N 20 41' N

20 42' N 20 42' N

20 43' N 20 43' N

20 44' N 20 44' N

99 37' W

99 37' W

99 36' W

99 36' W

99 35' W

99 35' W

99 34' W

99 34' W

99 33' W

99 33' W

99 32' W

99 32' W

99 31' W

99 31' W

99 30' W

99 30' W

99 29' W

99 29' W

99 28' W

99 28' W

99 27' W

99 27' W

99 26' W

99 26' W

99 25' W

99 25' W

99 24' W

99 24' W

99 23' W

99 23' W

99 22' W

99 22' W

99 21' W

99 21' W

99 20' W

99 20' W

99

20' W

99 20' W

0 51 2 3 4

ESCALA:

Km

ROCAGNEAINTRUSIVA

CALIZAFMELDOCTOR

LUTITAFMSOYATAL

FANGLOMERADOFMELMORRO

ANDESITABASLTICAXINDH

TOBARIOLTICAYETHAY/IGNIMBRITARIOLTICACARRIZAL

RIOLITAPONTIHU

CONGLOMERADOPOLIMCTICO

BASALTOSAUCILLO

COLUVINYALUVIN

INFERIOR

PALECENO-EOCENO

OLIGOCENO

MIOCENOTARDO

NEGENO

CRETCICOSUPERIOR

LITOLOGA SIMBOLOGA

FALLANORMAL

ZIMAPNREAURBANA

CARRETERA

1800 CURVASDENIVEL

PRESA

B-A

KLIPPE

35

Z IM -

2

2 MUESTRA

SEUDO-ESTRATIFICACIN

R

DIQUERIOLTICO

DIQUEBASLTICO-ANDESTICO

CABALGADURA

FALLANORMALCON

COMPONENTELATERAL

MONZONITA